Incidence rate of clinical mastitis on Canadian dairy farms

Colchicine can keep the viability of bacteria in mastitic milk by preventing leukocyte phagocytosis in dairy cow and goat

Despite the occurrence of mastitis, no bacteria were detected in any of the milk samples after culture. This is partially because the neutrophils present in milk phagocytose bacteria during milk preservation. In this study, we investigated whether colchicine inhibited the decrease in viable bacteria in milk by suppressing phagocytosis during preservation. The number of viable bacteria decreased when cow milk was preserved for 5 h. However, the addition of 0.1 and 1% colchicine significantly increased the number of viable bacteria (p < 0.05). The percentage of culture-negative cow's milk increased more than two-fold after 5 h compared to that at 0 h of preservation, however this percentage was significantly reduced by the addition of colchicine (p < 0.05). When goat milk with mastitis was incubated with bacteria (Escherichia coli, Klebsiella pneumoniae, and Staphylococcus aureus), the percentage of phagocytosed neutrophils decreased significantly with the addition of colchicine (p < 0.05). These results indicate that colchicine suppressed the decrease in the number of viable bacteria by preventing neutrophil phagocytosis during milk preservation. These findings may help in the identification of mastitis-causing bacteria and the selection of antibiotics for the treatment of mastitis.

Molecular characteristics and antimicrobial susceptibility profiles of bovine mastitis agents in western Türkiye

IMPORTANCE

Identifying bovine mastitis agents using molecular methods to reveal their phylogenetic relationships and antimicrobial resistance profiles is essential for developing up-to-date databases in mastitis cases that cause severe economic losses.

OBJECTIVE

This study examined bacterial mastitis agents in cows with clinical and subclinical mastitis observed in various dairy cattle farms to reveal their phylogenetic relationships and antibiotic resistance properties.

METHODS

Sixty-two clinical and subclinical bovine mastitis milk samples were collected from 15 dairy farms. The polymerase chain reaction (PCR) was used to amplify the 16S rRNA gene regions of the bacteria. The 16S rRNA gene sequences obtained from sequencing include the V4-V6 regions. The strains were compared using a similarity analysis method that produced phylogenetic trees using the Molecular Evolutionary Genetics Analysis 11 program. Antibiotic susceptibilities were determined using the Kirby-Bauer disk diffusion method.

RESULTS

Sixty-three bacteria were isolated and identified in this study. The most isolated bacteria from all mastitis cases were Staphylococcus spp. (30.2%), Escherichia coli (25.4%), Streptococcus spp. (14.3%), and Aerococcus spp. (7.9%), respectively. The phylogenetic trees were drawn from the 16S rRNA sequences. Some of these bacteria showed resistance to different types of antibiotics at varying rates.

CONCLUSIONS AND RELEVANCE

The bacteria isolated in this study originated from environmental sources. Regular cleaning of barns and proper hygiene practices are essential. Regular screenings for mastitis should be conducted in herds instead of the random or empirical use of antibiotics.

Role of mastitis in on-farm deaths of Finnish dairy cows

According to our recent necropsy-based study, mastitis is the most common underlying diagnosis of on-farm deaths in Finnish dairy cows. However, it remained unanswered to what extent mastitis has contributed to death of all necropsied cows. In the present study, based on histopathology, we detected one-third of the necropsied dairy cows having active inflammatory udder lesions (n = 110). The role of mastitis varied and was interpreted by causes of death (underlying, intermediate, immediate, other significant). Mastitis was most commonly the underlying (28%) or both immediate and underlying cause of death (48%), and only seldom was it the immediate (4%) or intermediate (4%) cause of death. Mastitis occurred either as the only cause leading to death (mastitis only, MO; 39%), or with many other contributing diseases (multiple diseases, MD; 61%), which were interacting with mastitis and together leading to death. Between these groups (MO vs. MD), time of mastitis occurrence during lactation, producer-reported duration of illness, clinical signs, and medication differed, as well the histopathologic severity of mastitis. The cases where mastitis was the only initial insult occurred evenly throughout the entire lactation, but the cases with many interacting diseases were clustered in early lactation. In MD cows, cases of mastitis occurred concurrently with metritis (31%), aspiration pneumonia (24%), acute trauma or dystocia (15%), or with other diseases, such as ketosis, hepatic lipidosis, rumenitis, and abomasal diseases. For a pathologist, the gross mastitis diagnosis was most challenging at the beginning of the lactation, especially if inflammation was mild to moderate, suggesting the value of histopathologic examination being highest at that time. Also, producers reported mastitis signs less frequently if cow had many simultaneously occurring diseases. Therefore, even if clinical signs of other diseases are present, the udder should be considered a potential cause of illness and should be examined, especially in dry and transition-period cows.

Decreased lactose percentage in milk associated with quarter health disorder and hyperketolactia, a proxy for negative energy balance, in dairy cows

Several studies have described variations in lactose content (LC) in dairy cows during udder quarter health disorder or negative energy balance (NEB). However, their joint effects on LC have never been described. This was the aim of a longitudinal observational study performed on 5 Quebec dairy farms using automatic milking systems. Quarter milk samples were collected every 14 d from 5 to 300 DIM. Quarter health status was described by combining SCC level (SCC- or SCC+: < or ≥100,000 cells/mL, respectively) and infectious status (Patho- or Patho+: absence or presence of pathogens on a milk culture, respectively). Cows with NEB in early lactation (DIM <70) were identified using milk BHB content: <0.15 mM = BHB-; 0.15 to 0.19 mM = BHB+; >0.19 mM = BHB++. A total of 14,505 quarter cisternal milk samples were collected from 380 lactating cows. The quarter LC was analyzed using a mixed linear regression model with the following fixed effects: quarter health status, parity, time interval between last milking and sampling, quarter milk yield (in kg/d), DIM, and herd. A random quarter intercept with a repeated measures correlation structure and a cow random intercept were also specified. The LC of SCC+ quarters was lower (-0.17 ± 0.013 percentage points) compared with LC of SCC- quarters for both primiparous and multiparous cows. Of the 162 bacterial species identified, only 8 species had a prevalence greater than 4.0%, and just 5 of them were associated with a reduction in LC: Staphylococcus aureus, Staphylococcus chromogenes, Streptococcus dysgalactiae, Staphylococcus epidermidis, and Staphylococcus simulans. Cows identified as BHB+ and BHB++ in early lactation had a lower LC (-0.05 ± 0.019 and -0.13 ± 0.020 percentage points, respectively) compared with BHB- cows. For BHB++ cows, in both parity groups the decrease in LC (-0.20 ± 0.025 percentage points) was higher in SCC+ quarters compared with SCC- quarters. Moreover, the additive effect of the quarter health status and NEB on milk LC was greater with larger increases in BHB. Our findings highlight the necessity to jointly take into consideration both quarter health status and milk BHB concentration when using LC as a biomarker for NEB.

Prevalence and spatial distribution of infectious diseases of dairy cattle in Ontario, Canada

We investigated the prevalence and spatial distribution of selected pathogens associated with infectious diseases of dairy cattle in Ontario, Canada. The cross-sectional study surveyed bulk tank milk for antibodies against bovine leukemia virus (BLV), Mycobacterium avium ssp. paratuberculosis (MAP), and Salmonella Dublin, and for the presence of mastitis pathogens (Staphylococcus aureus, Streptococcus agalactiae, Mycoplasma bovis). Between October 2021 and June 2022, bulk tank milk samples were obtained from every commercial dairy farm in Ontario (n = 3,286). Samples underwent ELISA testing for the presence of BLV, MAP, and S. Dublin antibodies, and quantitative PCR testing for the detection of specific antigens of pathogens associated with mastitis. Bayesian models were used to estimate prevalence, and spatial analysis was carried out to identify regional clusters of high pathogen prevalence. Prevalence varied for different pathogens, and BLV was widespread across dairy farms in Ontario, with an estimated prevalence of 88.3%. The prevalence of MAP, Staph. aureus and S. Dublin in Ontario dairy herds was 39.8%, 31.5%, and 5.1%, respectively. The vast majority of dairy herds in Ontario were free of intramammary infections caused by Strep. agalactiae and M. bovis. Clusters of increased positive test rates were detected for S. Dublin, MAP, and Staph. aureus, indicating potential geographic risk factors for pathogen transmission. For S. Dublin, an area of increased test positivity rates was detected in southwestern Ontario, close to the Canada-United States border where most of the dairy herds in Ontario are located. Conversely, a localized cluster of positive test outcomes involving 14 subdivisions located in the southeastern region of Ontario was detected for Staph. aureus. Findings from our survey highlight the importance of the testing of aggregated samples and conducting spatial analysis as part of disease surveillance programs, and for implementing risk-based trading approaches among dairy producers.

Dairy farmer's income, working time, and antimicrobial use under different dry cow therapy protocols

Mastitis is one of the most common diseases of dairy cattle. It has a high impact on farm economy, farmers' working time, and antimicrobial usage (AMU). Selective dry cow therapy (SDCT) is an effective means of reducing AMU without negatively affecting udder health. The objective of our study was to evaluate the impact of SDCT implementation on farmer's income, working time, and AMU, using a bioeconomic model. A stochastic dairy simulation model (DairyHealthSim) based on a weekly model was used to simulate herd dynamics, reproduction, milk production, culling decisions, health outcomes, and the management of health events. A specific module was developed for the simulation of quarter-level intramammary infection (IMI) acquisition and elimination during the lactation and dry-off periods, and 25 different farm settings were defined to represent herds with various udder health situations. We then defined 20 scenarios of SDCT by combining both the use of different thresholds of somatic cell count and milk bacteriology for treatment allocation and the use of internal teat sealant (ITS). All SDCT protocols had a low impact on farmer's income, and we identified some protocols with a positive farm gross margin (up to 15.83 CA$/dried- cow). We also found that adding an ITS to all cows led to greater economic gain. The application of SDCT had a low impact on farmers' working time, except when milk bacteriology was used for decision-making. Antimicrobial treatment to all cows above 200,000 cells/mL at last control, with the use of ITS on all cows, seems a good choice in most dairy farms. These findings could be used to convince farmers to adopt this strategy at dry-off.

Discriminating bovine mastitis pathogens by combining loop-mediated isothermal amplification and amplicon-binding split trehalase assay

Bovine mastitis is predominantly caused by intramammary infections with various Gram-positive and Gram-negative bacteria, requiring accurate pathogen identification for effective treatment and antimicrobial resistance prevention. Here, a novel diagnostic method was developed to detect mastitis pathogens in milk samples by combining loop-mediated isothermal amplification with a split enzyme biosensor whereby trehalase fragments were fused with a DNA-binding protein, SpoIIID. Three primer sets, LAMPstaph, LAMPstrep, and LAMPneg, harboring SpoIIID recognition sequences targeted Staphylococcus, Streptococcus, and Gram-negative pathogens, respectively. Limits of detection were determined for DNA extracted from bacterial culture and bacteria-spiked milk. The combined method detected as low as 2, 24, and 10 copies of genomic DNA of staphylococci, streptococci and Escherichia coli and 11 CFU/ml for milk spiked with Escherichia coli. Higher detection limits were observed for Gram-positive bacteria in spiked milk. When testing genomic DNA of 10 mastitis isolates at concentrations of 106 and 103 copies per reaction, no cross-reactivity was detected for LAMPstaph nor LAMPstrep, whereas the LAMPneg assay cross-reacted only with Corynebacterium sp. at the highest concentration. This combined method demonstrated the potential to distinguish mastitis pathogenic Gram types for a rapid decision of antimicrobial treatment without culturing.

Staphylococcal mastitis in dairy cows

Bovine mastitis is one of the most common diseases of dairy cattle. Even though different infectious microorganisms and mechanical injury can cause mastitis, bacteria are the most common cause of mastitis in dairy cows. Staphylococci, streptococci, and coliforms are the most frequently diagnosed etiological agents of mastitis in dairy cows. Staphylococci that cause mastitis are broadly divided into Staphylococcus aureus and non-aureus staphylococci (NAS). NAS is mainly comprised of coagulase-negative Staphylococcus species (CNS) and some coagulase-positive and coagulase-variable staphylococci. Current staphylococcal mastitis control measures are ineffective, and dependence on antimicrobial drugs is not sustainable because of the low cure rate with antimicrobial treatment and the development of resistance. Non-antimicrobial effective and sustainable control tools are critically needed. This review describes the current status of S. aureus and NAS mastitis in dairy cows and flags areas of knowledge gaps.

Evaluation of Point-of-Care Tests for Identification of Pathogens to Inform Clinical Mastitis Treatment Decisions in Pasture- and Confinement-Managed Dairy Cows in Australia

To support antimicrobial stewardship in livestock production, there is a growing array of point of care diagnostics to guide antimicrobial treatment. The primary objective of this observational study was to evaluate the diagnostic performance of 5 point of care tests currently available in Australia for guiding lactational treatment of non-severe clinical mastitis. A secondary objective was to describe the pathogen profiles of mastitis-causing organisms in cows managed in barns ("intensive") and on pasture ("non-intensive"). Foremilk samples (n = 641) were collected by farm staff in dairy herds in Australia (n = 30) and tested at a university laboratory using a reference test and 5 index tests. The reference test was aerobic culture on Trypticase Soy Agar with 5% sheep blood followed by MALDI-TOF for identification of isolates. The following point of care tests were evaluated as index tests: Accumast®, biplate, Check-Up, Mastatest®, and 3M Petrifilm. We found that 23% of samples were contaminated, with the median herd contamination prevalence being 22%. After excluding contaminated samples, the most common diagnoses (according to the reference test) in intensive herds were no growth (31.7%), Klebsiella spp. (28.1%), E. coli (15.0%), and Strep. uberis (8.4%). The most common diagnoses in non-contaminated samples from cows in non-intensive herds were Strep. uberis (35.0%), no growth (26.9%), and E. coli (13.3%). After 24 h of incubation, all index tests demonstrated limited diagnostic sensitivity for identification of pathogens of interest (range: 0.06 to 0.63). Diagnostic performance was better at the group-level, with sensitivity and specificity for identification of non-contaminated gram-positive growths (i.e., cases that are widely considered to be candidates for antimicrobial treatment) being 0.84 and 0.75 (biplate), 0.76 and 0.90 (Accumast), 0.89 and 0.79 (Check-Up), 0.67 and 0.83 (Petrifilm), and 0.55 and 0.81 (Mastatest). In intensive herds, 22.7 to 40% of cases were classified as antimicrobial treatment candidates by index tests, which was less than for cows in non-intensive herds (41.3 to 61.0%). Despite limited diagnostic reliability at genus and species level, and the need to ensure samples are collected aseptically, our findings indicate that implementation of selective treatment protocols using the tests evaluated in this study would likely reduce antimicrobial usage in Australian herds.

DNA methylation haplotype block signatures responding to Staphylococcus aureus subclinical mastitis and association with production and health traits

BACKGROUND

DNA methylation has been documented to play vital roles in diseases and biological processes. In bovine, little is known about the regulatory roles of DNA methylation alterations on production and health traits, including mastitis.

RESULTS

Here, we employed whole-genome DNA methylation sequencing to profile the DNA methylation patterns of milk somatic cells from sixteen cows with naturally occurring Staphylococcus aureus (S. aureus) subclinical mastitis and ten healthy control cows. We observed abundant DNA methylation alterations, including 3,356,456 differentially methylated cytosines and 153,783 differential methylation haplotype blocks (dMHBs). The DNA methylation in regulatory regions, including promoters, first exons and first introns, showed global significant negative correlations with gene expression status. We identified 6435 dMHBs located in the regulatory regions of differentially expressed genes and significantly correlated with their corresponding genes, revealing their potential effects on transcriptional activities. Genes harboring DNA methylation alterations were significantly enriched in multiple immune- and disease-related pathways, suggesting the involvement of DNA methylation in regulating host responses to S. aureus subclinical mastitis. In addition, we found nine discriminant signatures (differentiates cows with S. aureus subclinical mastitis from healthy cows) representing the majority of the DNA methylation variations related to S. aureus subclinical mastitis. Validation of seven dMHBs in 200 cows indicated significant associations with mammary gland health (SCC and SCS) and milk production performance (milk yield).

CONCLUSIONS

In conclusion, our findings revealed abundant DNA methylation alterations in milk somatic cells that may be involved in regulating mammary gland defense against S. aureus infection. Particularly noteworthy is the identification of seven dMHBs showing significant associations with mammary gland health, underscoring their potential as promising epigenetic biomarkers. Overall, our findings on DNA methylation alterations offer novel insights into the regulatory mechanisms of bovine subclinical mastitis, providing further avenues for the development of effective control measures.

Prediction of key milk biomarkers in dairy cows through milk mid-infrared spectra and international collaborations

At the individual cow level, suboptimum fertility, mastitis, negative energy balance, and ketosis are major issues in dairy farming. These problems are widespread on dairy farms and have an important economic impact. The objectives of this study were (1) to assess the potential of milk mid-infrared (MIR) spectra to predict key biomarkers of energy deficit (citrate, isocitrate, glucose-6 phosphate [glucose-6P], free glucose), ketosis (β-hydroxybutyrate [BHB] and acetone), mastitis (N-acetyl-β-d-glucosaminidase activity [NAGase] and lactate dehydrogenase), and fertility (progesterone); (2) to test alternative methodologies to partial least squares (PLS) regression to better account for the specific asymmetric distribution of the biomarkers; and (3) to create robust models by merging large datasets from 5 international or national projects. Benefiting from this international collaboration, the dataset comprised a total of 9,143 milk samples from 3,758 cows located in 589 herds across 10 countries and represented 7 breeds. The samples were analyzed by reference chemistry for biomarker contents, whereas the MIR analyses were performed on 30 instruments from different models and brands, with spectra harmonized into a common format. Four quantitative methodologies were evaluated to address the strongly skewed distribution of some biomarkers. Partial least squares regression was used as the reference basis, and compared with a random modification of distribution associated with PLS (random-downsampling-PLS), an optimized modification of distribution associated with PLS (KennardStone-downsampling-PLS), and support vector machine (SVM). When the ability of MIR to predict biomarkers was too low for quantification, different qualitative methodologies were tested to discriminate low versus high values of biomarkers. For each biomarker, 20% of the herds were randomly removed within all countries to be used as the validation dataset. The remaining 80% of herds were used as the calibration dataset. In calibration, the 3 alternative methodologies outperform the PLS performances for the majority of biomarkers. However, in the external herd validation, PLS provided the best results for isocitrate, glucose-6P, free glucose, and lactate dehydrogenase (coefficient of determination in external herd validation [R2v] = 0.48, 0.58, 0.28, and 0.24, respectively). For other molecules, PLS-random-downsampling and PLS-KennardStone-downsampling outperformed PLS in the majority of cases, but the best results were provided by SVM for citrate, BHB, acetone, NAGase, and progesterone (R2v = 0.94, 0.58, 0.76, 0.68, and 0.15, respectively). Hence, PLS and SVM based on the entire dataset provided the best results for normal and skewed distributions, respectively. Complementary to the quantitative methods, the qualitative discriminant models enabled the discrimination of high and low values for BHB, acetone, and NAGase with a global accuracy around 90%, and glucose-6P with an accuracy of 83%. In conclusion, MIR spectra of milk can enable quantitative screening of citrate as a biomarker of energy deficit and discrimination of low and high values of BHB, acetone, and NAGase, as biomarkers of ketosis and mastitis. Finally, progesterone could not be predicted with sufficient accuracy from milk MIR spectra to be further considered. Consequently, MIR spectrometry can bring valuable information regarding the occurrence of energy deficit, ketosis, and mastitis in dairy cows, which in turn have major influences on their fertility and survival.

Estimation of epidemiological cut-off values for eight antibiotics used for treatment of bovine mastitis caused by Streptococcus uberis and Streptococcus dysgalactiae subsp. dysgalactiae

Interpretive criteria for antimicrobial susceptibility testing are lacking for most antimicrobials used for bovine streptococcal mastitis. The objectives of this study were to determine (tentative) epidemiological cut-off ((T)ECOFF) values for clinically relevant antibiotics used for treatment of bovine mastitis, and to estimate the proportion of acquired resistance (non-wild-types) in Streptococcus dysgalactiae subsp. dysgalactiae and Streptococcus uberis. A total of 255 S. uberis and 231 S. dysgalactiae subsp. dysgalactiae isolates were obtained in Denmark and Norway from bovine mastitis. The isolates were tested for susceptibility to 10 antibiotics using broth microdilution. In accordance with the European Committee on Antimicrobial Susceptibility Testing (EUCAST) standard operating procedure, additional published MIC distributions were included for the estimation of ECOFFs for cloxacillin, cephapirin, lincomycin and tylosin, and TECOFFs for amoxicillin, benzylpenicillin, cephapirin and oxytetracycline. The proportion of non-wild-type (NWT) isolates for the beta-lactams was significantly higher in the Danish S. uberis (45-55%) compared to the Norwegian isolates (10-13%). For oxytetracycline, the proportion of NWT was significantly higher in the Danish isolates, both for S. uberis (28% vs. 3%) and S. dysgalactiae (22% vs. 0%). A bridging study testing in parallel MICs in a subset of isolates (n = 83) with the CLSI-specified and the EUCAST-specified broths showed excellent correlation between the MICs obtained with the two methods. The new ECOFFs and TECOFFs proposed in this study can be used for surveillance of antimicrobial resistance, and - for antimicrobials licensed for streptococcal bovine mastitis - as surrogate clinical breakpoints for predicting their clinical efficacy for this indication.

Effects of dietary rumen-protected choline supplementation to periparturient dairy cattle on inflammation and metabolism in mammary and liver tissue during an intramammary lipopolysaccharide challenge

The objective of this experiment was to examine the effects of supplementation and dose of rumen-protected choline (RPC) on markers of inflammation and metabolism in liver and mammary tissue during an intramammary lipopolysaccharide (LPS) challenge. Parous Holstein cows were blocked by calving month and randomly assigned within block to receive 45 g/d of RPC (20.4 g/d of choline ions; CHOL45), 30 g/d of RPC (13.6 g/d of choline ions; CHOL30), or no RPC (CON) as a top-dress starting 24 d before expected calving until 21 d postpartum. Cows were alternately assigned within treatment group to either receive an intramammary LPS challenge (200 μg in each rear quarter; Escherichia coli O111:B4) or not at 17 DIM (CHOL45, n = 9; CHOL45-LPS, n = 9; CHOL30, n = 11; CHOL30-LPS, n = 10; CON, n = 10; CON-LPS, n = 9). Hepatic and mammary tissues were collected from all cows on d 17 postpartum. Hepatic and mammary tissues were collected at ∼7.5 and 8 h, respectively, after the LPS challenge. An additional mammary biopsy was conducted on LPS-challenged cows (CHOL45-LPS, CHOL30-LPS, and CON-LPS) at 48 h postchallenge. Hepatic and mammary RNA copy numbers were quantified for genes involved in apoptosis, methylation, inflammation, oxidative stress, and mitochondrial function using NanoString technology. Targeted metabolomics was conducted only on mammary tissue samples (both 8 and 48 h biopsies) to quantify 143 metabolites including choline metabolites, amino acids, biogenic amines and derivatives, organic acids, carnitines, and glucose. Hepatic IFNG was greater in CHOL45 as compared with CON in unchallenged cows, suggesting an improvement in type 1 immune responses. Hepatic CASP3 was greater in CHOL45-LPS as compared with CON-LPS, suggesting greater apoptosis. Mammary IL6 was reduced in CHOL30-LPS cows as compared with CHOL45-LPS and CON-LPS (8 and 48 h). Mammary GPX4 and COX5A were reduced in CHOL30-LPS as compared with CON-LPS (8 h), and SDHA was reduced in CHOL30-LPS as compared with CON-LPS (8 and 48 h). Both CHOL30-LPS and CHOL45-LPS cows had lesser mammary ATP5J than CON-LPS, suggesting that dietary RPC supplementation altered mitochondrial function following LPS challenge. Treatment did not affect mammary concentrations of any metabolite in unchallenged cows, and only 4 metabolites were affected by dietary RPC supplementation in LPS-challenged cows. Mammary concentrations of isobutyric acid and 2 acyl-carnitines (C4:1 and C10:2) were reduced in CHOL45-LPS as compared with CHOL30-LPS and CON-LPS. Taken together, reductions in medium- and short-chain carnitines along with an increase in long-chain carnitines in mammary tissue from CHOL45-LPS cows suggests less fatty acid entry into the β oxidation pathway. Although the intramammary LPS challenge profoundly affected markers for inflammation and metabolism in liver and mammary tissue, dietary RPC supplementation had minimal effects on inflammatory markers and the mammary metabolome.

Comparison of Minimum Inhibitory Concentrations of Selected Antimicrobials for Non-Aureus Staphylococci, Enterococci, Lactococci, and Streptococci Isolated from Milk Samples of Cows with Clinical Mastitis

The objective of this study was to compare the minimum inhibitory concentrations of antimicrobials included in a commercial broth microdilution panel among Gram-positive pathogens that caused non-severe clinical mastitis on three Michigan dairy farms. Duplicate quarter milk samples were collected from eligible quarters of cows enrolled in a randomized clinical trial, cultured in a university laboratory, and identified using MALDI-TOF. Etiologies were grouped by genus as Enterococcus species (n = 11), Lactococcus species (n = 44), non-aureus Staphylococcus species (n = 39), or Streptococcus species (n = 25). Minimum inhibitory concentrations (MICs) were determined using the mastitis panel of a commercially available broth microdilution test. In vitro susceptibility was determined using approved guidelines and included breakpoints for mastitis pathogens, or when not available, breakpoints from other species. Most isolates were inhibited at or below breakpoints that demonstrated in vitro susceptibility. The proportions of susceptible isolates varied among pathogens for pirlimycin, penicillin, and tetracycline. The greatest proportion of resistance was observed for pirlimycin, tetracycline, and sulfadimethoxine. Survival analysis was performed to evaluate differences in MICs among pathogen groups. MIC values varied among pathogens for ceftiofur, cephalothin, erythromycin, penicillin, pirlimycin, and tetracycline. However, nearly all isolates were susceptible to ceftiofur and cephalothin, indicating that pathogen differences in MIC are not likely clinically relevant, as these are the two most commonly administered mastitis treatments in the United States. While differences in vitro susceptibility were observed for some antimicrobials, susceptibility was high to cephalosporin-based IMM treatments that are most commonly used and did not vary among pathogens.

Association between somatic cell count or morbidity of chronic subclinical mastitis and longevity in dairy herds in Eastern Hokkaido, Japan: a cross-sectional study

An epidemiological analysis was conducted on production records in Hokkaido, Japan, to investigate the potential association between improved milk quality and longevity outcomes. The study found significant variations in herd somatic cell count levels and chronic subclinical mastitis morbidity based on geographical area and herd size. The analysis also revealed a positive correlation between herd somatic cell count and chronic subclinical mastitis morbidity. Although the hypothesis of a causal link between milk quality and longevity was examined, no such association was found. However, intensive assistance for identified high-risk areas and farms is expected to enhance overall milk quality.

Adoption and decision factors regarding selective treatment of clinical mastitis on Canadian dairy farms

As clinical mastitis (CM) treatments are responsible for a large portion of antimicrobial use on dairy farms, many selective CM treatment protocols have been developed and evaluated against a blanket treatment approach of CM cases. Selective treatment protocols use outcomes of diagnostic tests to exclude CM cases from antimicrobial treatment when they are unlikely to benefit. To tailor interventions to increase uptake of selective treatment strategies, a comprehension of current on-farm treatment practices and factors affecting treatment decisions is vital. Two questionnaires were conducted among 142 farms across 5 provinces participating in the Canadian Dairy Network for Antimicrobial Stewardship and Resistance in this cross-sectional study. Self-reported adoption of selective CM treatments by dairy farmers was 64%, with median of 82% of cows treated in those herds using selective treatment. Using logistic regression models, the odds to implement a selective CM treatment protocol increased with a decreasing average cow somatic cell count. No other associations were identified between use of a selective CM treatment protocol and farm characteristics (herd size, CM incidence, province, milking system, and housing system). Three subsets of farmers making cow-level CM treatment decisions were identified using a cluster analysis approach: those who based decisions almost exclusively on severity of clinical signs, those who used various udder health indicators, and farmers who also incorporated more general cow information such as production, age, and genetics. When somatic cell count was considered, the median threshold used for treating was >300,000 cells/mL at the last Dairy Herd Improvement test. Various thresholds were present among those considering CM case history. Veterinary laboratories were most frequently used for bacteriological testing. Test results were used to start, change, and stop treatments. Regardless of protocol, reasons for antimicrobial treatment withheld included cow being on a cull list, having a chronic intramammary infection, or being at end of lactation (i.e., close to dry off). If clinical signs persisted after treatment, farmers indicated that they would ask veterinarians for advice, stop treatment, or continue with the same or different antibiotics. Results of this study can be used to design interventions targeting judicious mastitis-related antimicrobial use, and aid discussions between veterinarians and dairy producers regarding CM-related antimicrobial use.

Effects of dietary rumen-protected choline supplementation to periparturient dairy cattle on inflammation, metabolism, and performance during an intramammary lipopolysaccharide challenge

Recent studies have suggested that dietary rumen-protected choline (RPC) supplementation can modulate immune function, attenuate inflammation, and improve performance in periparturient dairy cattle; however, this has yet to be evaluated during a mastitis challenge. Therefore, the objective of this study was to examine the effects of supplementation and dose of RPC on metabolism, inflammation, and performance during an intramammary lipopolysaccharide (LPS) challenge. Parous Holstein cows (parity, mean ± SD, 1.9 ± 1.1 at enrollment) were blocked by calving month and randomly assigned within block to receive either 45 g/d of RPC (20.4 g/d of choline ions; CHOL45, n = 18), 30 g/d of RPC (13.6 g/d of choline ions; CHOL30, n = 21), or no RPC (CON, n = 19) as a top-dress starting 24 d before expected calving until 21 d postpartum. Cows were alternately assigned within treatment group to either receive an intramammary LPS challenge (200 μg in each rear quarter; Escherichia coli O111:B4) or not at 17 DIM. Before the challenge, CHOL45 and CHOL30 cows produced 3.4 and 3.8 (±1.2 SED) kg/d more milk than CON, respectively. Dietary RPC supplementation did not mitigate the milk loss associated with the intramammary LPS challenge; however, CHOL45 and CHOL30 cows produced 3.1 and 3.5 (±1.4 SED) kg/d more milk than CON, respectively in the carryover period (22 to 84 DIM). Dietary RPC supplementation enhanced plasma β-hydroxybutyrate (BHB) concentrations before the LPS challenge, and increased plasma nonesterified fatty acids (NEFA) and acetylcarnitine concentrations during the LPS challenge, potentially reflecting greater adipose tissue mobilization, fatty acid transport and oxidation. Aside from trimethylamine N-oxide and sarcosine, which were increased in CHOL45-LPS as compared with CON-LPS, most other choline metabolite concentrations in plasma were unaffected by treatment, likely because more choline was being secreted in milk. Plasma lactic acid concentrations were decreased in CHOL45-LPS and CHOL30-LPS as compared with CON-LPS, suggesting a reduction in glycolysis or an enhancement in the flux through the lactic acid cycle to support gluconeogenesis. Plasma concentrations of fumaric acid, a byproduct of AA catabolism and the urea cycle, were increased in both choline groups as compared with CON-LPS during the LPS challenge. Cows in the CHOL45 group had greater plasma antioxidant potential before the LPS challenge and reduced plasma methionine sulfoxide concentrations during the LPS challenge compared with CON-LPS, suggesting an improvement in oxidant status. Nevertheless, concentrations of inflammatory markers such as haptoglobin and tumor necrosis factor α (TNFα) were not affected by treatment. Taken together, our data suggest that the effects of dietary RPC supplementation on milk yield could be mediated through metabolic pathways and are unlikely to be related to the resolution of inflammation in periparturient dairy cattle. Lastly, dose responses to dietary RPC supplementation were not found for various economically important outcomes including milk yield, limiting the justification for feeding a greater dietary RPC dose in industry.

A Cross-Sectional Study of Risk Factors Affecting Milk Quality in Dairy Cows

Despite years of research devoted to bovine mastitis, the disease remains a serious problem in dairy cattle, causing economic losses to the dairy industry worldwide due to reduced milk yield, lower milk quality, drug costs and early culling of cows. The aim of this study is to determine the importance of several risk factors affecting milk quality in dairy cows, as well as to highlight proper milking techniques. A cross-sectional study was performed in one Greek dairy farm with the inclusion of a total of 1004 Holstein Friesian cows in the study. The udder and teat traits were recorded for each cow, while individual milk samples were used to estimate the somatic cell count (SCC) and gross milk composition. The traits recorded were examined as potential risk factors affecting milk quality using the Akaike information criterion (AIC) and the algorithm stepAIC to select the best linear regression model which explains the data. Overall, the prevalence of mastitis was ca. 9%. With an increase in the lactation period, the SCC increased (p ≤ 0.05) while fat (p ≤ 0.05), protein (p ≤ 0.001) and lactose (p ≤ 0.001) content decreased. Teat hyperkeratosis increased the SCC (p ≤ 0.05) and decreased P content (p ≤ 0.05). Proper husbandry management and milking procedures are considered essential to maintain milk quality of high standards.

Association between management practices and estimated mastitis incidence and milk losses on robotic dairy farms

This study aims to describe the relation between farm-level management factors and estimated farm-level mastitis incidence and milk loss traits (MIMLT) at dairy farms with automated milking systems. In this observational study, 43 commercial dairy farms in Belgium and the Netherlands were included and 148 'management and udder health related variables' were obtained during a farm visit through a farm audit and survey. The MIMLT were estimated from milk yield data. Quarter-level milk yield perturbations that were caused by presumable mastitis cases (PMC) were selected based on quarter-level milk yield and electrical conductivity. On average, 57.6 ± 5.4% of the identified milk yield perturbations complied with our criteria. From these PMC, 3 farm-level MIMLT were calculated over a one-year period around the farm visit date: (1) the 'average number of PMC per cow per year', (2) the 'absolute milk loss per cow per day', calculated as the farm-level sum of all milk losses during PMC in one year, divided by the average number of lactating cows and the number of days, and (3) the 'relative milk loss', calculated as the farm-level sum of milk losses during PMC in one year, divided by the estimated total production in the absence of PMC. The 'average number of PMC per cow per year' was on average 1.81 ± 0.47. The PMC caused an average milk loss of 0.77 ± 0.26 kg per lactating cow per day, which corresponded to an average production loss of 2.38 ± 0.82% of the expected production in the absence of PMC. We performed a principal component regression (PCR) analysis to link the 3 MIMLT to the 'management and udder health related variables', whilst reducing the multicollinearity and the number of dimensions. The first principal component was mainly related to 'milking system brand, maintenance and settings'. The second component mainly linked to average productivity and somatic cell counts, whereas the third component mainly contained variables linked with mastitis management, treatment, and biosecurity. The 3 PCR models had R² ranging from 0.46 (for absolute milk loss per cow per day) to 0.57 (for relative milk loss). For all models, the second PC had the largest effect size. This analysis raises awareness of the impact of management factors on a factual basis and provides handles to take management actions to improve udder health.

Management Practices of Bovine Mastitis and Milk Quality on Egyptian Dairies

Milk production continues to be the main source of income for dairy producers, and mastitis continues to be the major health challenge for dairy cows worldwide. The objective of the current study was to describe the different management practices implemented in Egyptian dairies, which may influence mastitis and improve milk quality. An in-person survey was completed with herd managers and owners of 20 Egyptian dairies selected using a stratified random sample from four of Egypt's milk sheds. The questionnaire included 80 questions that inquired about herd demographics, mastitis status and control, milking practices, and management practices of the study dairies. Statistical analyses included descriptive statistics, multiple factor analysis (MFA), and hierarchical clustering to identify the important principal components and different dairy clusters. Of the surveyed herds, 69.50% had less than 500 lactating cows, with Holstein as the main cow breed. The reported average milk production on the study herds was 31.1 (SE ± 1.10) Kg/cow/day. Housing of lactating, dry, and close-up cows was in open lots. The majority of the dairies milked cows were three times per day (90.63%), the remaining milked cows four (5.00%) or a mix of four and three times per day. Furthermore, herringbone parlor design was the most common parlor design (66.79%) in the study dairies. The most common disinfectants used for both pre- and post-milking teat dip were iodine-based, 90.0% and 95.0%, respectively, while 52.16% of the dairies reported that their milkers wore gloves during milking. The reported mean annual percentage of mastitis was 52.3%, as a percent of the milking herd. The study dairies reported the inspection of udder health through either visual inspection (95.00%), udder hygiene score (86.88%), teat end score (71.88%), and/or using CMT (54.91%). Contagious mastitis pathogens were reported in 45.2% of the study herds. More than 50% of the study herds relied on importing pregnant cows or pregnant heifers as replacements. Multiple factor analysis identified 20 questions and represented 5 components of variability related to mastitis on dairies. The current survey of Egyptian dairies described the herd demographics and different management practices related to mastitis control and prevention. All the study dairies relied on the blanket intramammary antimicrobial drugs at dry off when current research elsewhere has identified selective dry cow therapy as an integral component of antimicrobial stewardship on dairies. Further research is required to identify the association between different management factors and the occurrence of mastitis.

Virulence Mechanisms of Staphylococcal Animal Pathogens

Staphylococci are major causes of infections in mammals. Mammals are colonized by diverse staphylococcal species, often with moderate to strong host specificity, and colonization is a common source of infection. Staphylococcal infections of animals not only are of major importance for animal well-being but have considerable economic consequences, such as in the case of staphylococcal mastitis, which costs billions of dollars annually. Furthermore, pet animals can be temporary carriers of strains infectious to humans. Moreover, antimicrobial resistance is a great concern in livestock infections, as there is considerable antibiotic overuse, and resistant strains can be transferred to humans. With the number of working antibiotics continuously becoming smaller due to the concomitant spread of resistant strains, alternative approaches, such as anti-virulence, are increasingly being investigated to treat staphylococcal infections. For this, understanding the virulence mechanisms of animal staphylococcal pathogens is crucial. While many virulence factors have similar functions in humans as animals, there are increasingly frequent reports of host-specific virulence factors and mechanisms. Furthermore, we are only beginning to understand virulence mechanisms in animal-specific staphylococcal pathogens. This review gives an overview of animal infections caused by staphylococci and our knowledge about the virulence mechanisms involved.

Incidence rate, risk factors, and bacterial causes of clinical mastitis on dairy farms in Hawassa City, southern Ethiopia

Mastitis is the most common disease of dairy cattle worldwide, causing economic losses due to reduced yield and poor quality of milk. It is of particular concern in Ethiopia, where effective prevention and control practices are lacking. The objective of the present prospective longitudinal study was to estimate the incidence rate of clinical mastitis (CM), identify the risk factors, isolate the bacterial agents, and determine the risk of recurrence. For this purpose, a total of 217 lactating cows were followed up every two weeks from calving to drying off or the end of the study period. Of these, 79 (36.41%) developed CM, of which 23% had recurrent infections in the same or a different quarter. The overall incidence rate of CM was 83.72 (95% CI: 63.2-98.2) cases per 100 cow-years at risk. In the multivariable Cox regression model, the risk of CM was found to be significantly higher in multiparous cows (HR = 1.96; p = 0.03), in cows with a history of mastitis (HR = 2.04; p = 0.030), in cows that had severely keratinized teat end condition (HR = 7.72; p < 0.001) and in cows kept in poorly cleaned barns (HR = 1.89; p = 0.007). The pathogenic bacteria isolated from mastitis-positive cows were Staphylococcus aureus (28.1%), E. coli (21.1%), Bacillus spp. (14%), Streptococcus spp. (14%), coagulase-negative staphylococci (12.3%), non aureus staphylococci (5.3%), Enterobacter spp. (3.5%), Klebsiella spp. (1.8%), Corynebacterium spp. (1.8%), and Proteus spp. (1.8%). The high incidence rate of CM in the present study shows that the disease spreads rapidly and can be responsible for a significant economic loss to milk producers in the study area. Therefore, raising awareness among dairy farmers, early detection and treatment of cases, post-milking teat disinfection, improvement of the hygienic status of cows and barns, use of dry cow therapy, and culling of chronic cases are recommended as viable measures to prevent and control clinical mastitis in the study area.

Status of udder health performance indicators and implementation of on farm monitoring on German dairy cow farms: results from a large scale cross-sectional study

Regional benchmarking data enables farmers to compare their animal health situation to that of other herds and identify areas with improvement potential. For the udder health status of German dairy cow farms, such data were incomplete. Therefore, the aim of this study was (1) to describe the incidence of clinical mastitis (CM), (2) to describe cell count based udder health indicators [annual mean test day average of the proportion of animals without indication of mastitis (aWIM), new infection risk during lactation (aNIR), and proportion of cows with low chance of cure (aLCC); heifer mastitis rate (HM)] and their seasonal variation, and (3) to evaluate the level of implementation of selected measures of mastitis monitoring. Herds in three German regions (North: n = 253; East: n = 252, South: n = 260) with different production conditions were visited. Data on CM incidence and measures of mastitis monitoring were collected via structured questionnaire-based interviews. Additionally, dairy herd improvement (DHI) test day data from the 365 days preceding the interview were obtained. The median (Q0.1, Q0.9) farmer reported incidence of mild CM was 14.8% (3.5, 30.8%) in North, 16.2% (1.9, 50.4%) in East, and 11.8% (0.0, 30.7%) in South. For severe CM the reported incidence was 4.0% (0.0, 12.2%), 2.0% (0.0, 10.8%), and 2.6% (0.0, 11.0%) for North, East, and South, respectively. The median aWIM was 60.7% (53.4, 68.1%), 59.0% (49.7, 65.4%), and 60.2% (51.5, 67.8%), whereas the median aNIR was 17.1% (13.6, 21.6%), 19.9% (16.2, 24.9%), and 18.3% (14.4, 22.0%) in North, East, and South, respectively with large seasonal variations. Median aLCC was ≤1.1% (≤ 0.7%, ≤ 1.8%) in all regions and HM was 28.4% (19.7, 37.2%), 35.7% (26.7, 44.2%), and 23.5% (13.1, 35.9%), in North, East and South, respectively. Participation in a DHI testing program (N: 95.7%, E: 98.8%, S: 89.2%) and premilking (N: 91.1%, E: 93.7%, S: 90.2%) were widely used. Several aspects of udder health monitoring, including exact documentation of CM cases, regular microbiological analysis of milk samples and the use of a veterinary herd health consultancy service were not applied on many farms. The results of this study can be used by dairy farmers and their advisors as benchmarks for the assessment of the udder health situation in their herds.

Invited review: Selective treatment of clinical mastitis in dairy cattle

Treatment of clinical mastitis (CM) and use of antimicrobials for dry cow therapy are responsible for the majority of animal-defined daily doses of antimicrobial use (AMU) on dairy farms. However, advancements made in the last decade have enabled excluding nonsevere CM cases from antimicrobial treatment that have a high probability of cure without antimicrobials (no bacterial causes or gram-negative, excluding Klebsiella spp.) and cases with a low bacteriological cure rate (chronic cases). These advancements include availability of rapid diagnostic tests and improved udder health management practices, which reduced the incidence and infection pressure of contagious CM pathogens. This review informed an evidence-based protocol for selective CM treatment decisions based on a combination of rapid diagnostic test results, review of somatic cell count and CM records, and elucidated consequences in terms of udder health, AMU, and farm economics. Relatively fast identification of the causative agent is the most important factor in selective CM treatment protocols. Many reported studies did not indicate detrimental udder health consequences (e.g., reduced clinical or bacteriological cures, increased somatic cell count, increased culling rate, or increased recurrence of CM later in lactation) after initiating selective CM treatment protocols using on-farm testing. The magnitude of AMU reduction following a selective CM treatment protocol implementation depended on the causal pathogen distribution and protocol characteristics. Uptake of selective treatment of nonsevere CM cases differs across regions and is dependent on management systems and adoption of udder health programs. No economic losses or animal welfare issues are expected when adopting a selective versus blanket CM treatment protocol. Therefore, selective CM treatment of nonsevere cases can be a practical tool to aid AMU reduction on dairy farms.

Antimicrobial Usage and Detection of Multidrug-Resistant Staphylococcus aureus: Methicillin- and Tetracycline-Resistant Strains in Raw Milk of Lactating Dairy Cattle

Staphylococcus aureus is a prominent cause of food-borne diseases worldwide. Enterotoxigenic strains of this bacteria are frequently found in raw milk, and some of these strains are resistant to antimicrobials, posing a risk to consumers. The main objectives of this study were to determine the antimicrobial resistance pattern of S. aureus in raw milk and to detect the presence of mecA and tetK genes in it. A total of 150 milk samples were obtained aseptically from lactating cattle, including Holstein Friesian, Achai, and Jersey breeds, maintained at different dairy farms. The milk samples were checked for the presence of S. aureus, and it was detected in 55 (37%) of them. The presence of S. aureus was verified by culturing on selective media, gram staining, and performing coagulase and catalase tests. Further confirmation was performed through PCR with a species-specific thermonuclease (nuc) gene. Antimicrobial susceptibility testing of the confirmed S. aureus was then determined by using the Kirby-Bauer disc diffusion technique. Out of the 55 confirmed S. aureus isolates, 11 were determined to be multidrug-resistant (MDR). The highest resistance was found to penicillin (100%) and oxacillin (100%), followed by tetracycline (72.72%), amikacin (27.27%), sulfamethoxazole/trimethoprim (18.18%), tobramycin (18.18%), and gentamycin (9.09%). Amoxicillin and ciprofloxacin were found to be susceptible (100%). Out of 11 MDR S. aureus isolates, the methicillin resistance gene (mecA) was detected in 9 isolates, while the tetracycline resistance gene (tetK) was found in 7 isolates. The presence of these methicillin- and tetracycline-resistant strains in raw milk poses a major risk to public health, as they can cause food poisoning outbreaks that can spread rapidly through populations. Our study concludes that out of nine empirically used antibiotics, amoxicillin, ciprofloxacin, and gentamicin were highly effective against S. aureus compared to penicillin, oxacillin, and tetracycline.

Estimates of dairy herd health indicators of mastitis, ketosis, inter-calving interval, and fresh cow replacement in the Piedmont region, Italy

Test-day milk analysis has largely been used to study health and performance parameters in dairy cows. In this study, we estimated four health indicators of dairy cows using test-day data. Our purpose was to estimate (1) mastitis incidence rate, prevalence, and the probability of recovery; (2) the incidence proportion of ketosis; (3) the duration of inter-calving interval; and (4) the risk of a fresh cow being replaced, in a large cohort of dairy herds in the Piedmont region (Italy). We retrospectively analysed test day records of 261,121 lactating cows and 1315 herds during five years (2015-2020). Mastitis was defined by somatic cell count and ketosis by fat-to-protein ratio. Calving dates were used to calculate ICI and to estimate the removal of a fresh cow from the herd. Mixed-effect generalized linear models were used to adjust for unmeasured herd-level risk factors. The risk of mastitis increased by 120% with parity (Odds ratio [OR] = 2.20, confidence interval [CI]: 2.17 - 2.23), by 7% by months in milking (OR = 1.07, CI: 1.07 - 1.07), and even more if the cow was already affected during the same lactation (OR = 8.74, CI: 8.67 - 8.82). Lactose concentration on the previous test day was the best positive prognostic factor for mastitis recovery (OR = 1.12, CI: 1.08 - 1.17). Ketosis risk was the highest between 3rd and 4th lactations and itself increased the risk of having ICI longer than 440 days (OR = 1.12, CI: 1.02 - 1.22), and fresh-cow removal (OR = 1.75, CI: 1.58 - 1.93). Also, the removal of fresh cows was more likely when mastitis (OR = 1.31, CI: 1.19 - 1.45) or long ICI (OR = 1.34, CI: 1.22 - 1.48) occurred. For each health indicator, herd-level risk factors had an important role (18-56% of within-herd covariance). Our results indicate that milk analysis could be also useful for predicting mastitis, its cure rate, and ketosis. Cow-level risk factors are not enough to explain the risk of these issues. By studying a large population over a long period, this study provides an updated estimate of dairy cow health indicators in Piedmont (north-western Italy), useful for benchmarking dairy herds.

Evaluation of reticuloruminal temperature for the prediction of clinical mastitis in dairy cows challenged with Streptococcus uberis

Automated monitoring devices have become increasingly utilized in the dairy industry, especially for monitoring or predicting disease status. While multiple automated monitoring devices have been developed for the prediction of clinical mastitis (CM), limitations in performance or applicability remain. The aims of this study were to (1) detect variations in reticuloruminal temperature (RRT) relative to an experimental intramammary challenge with Streptococcus uberis and (2) evaluate alerts generated automatically based on variation in RRT to predict initial signs of CM in the challenged cows based on severity of clinical signs and the concentration of bacteria (cfu/mL) in the infected quarter separately. Clinically healthy Holstein cows without a history of CM in the 60 d before the experiment (n = 37, parity 1 to 5, ≥120 d in milk) were included if they were microbiologically negative and had a somatic cell count under 200,000 cells/mL based on screening of quarter milk samples 1 wk before challenge. Each cow received an intra-reticuloruminal automated monitoring device before the trial and was challenged with 2,000 cfu of Strep. uberis 0140J in 1 rear quarter. Based on interrupted time series analysis, intramammary challenge with Strep. uberis increased RRT by 0.54°C [95% confidence interval (CI): 0.41, 0.66] at 24 h after the challenge, which remained elevated until the end of the study. Alerts based on RRT correctly classified 78.3% (95% CI: 65.8, 87.9) of first occurrences of CM at least 24 h in advance, with a sensitivity of 70.0% (95% CI: 50.6, 85.3) and a specificity of 86.7% (95% CI: 69.3, 96.2). The accuracy of CM for a given severity score was 90.9% (95% CI: 70.8, 98.9) for mild cases, 85.2% (95% CI: 72.9, 93.4) for moderate cases, and 92.9% (95% CI: 66.1, 99.8) for severe cases. Test characteristics of the RRT alerts to predict initial signs of CM improved substantially after bacterial count in the challenged quarter reached 5.0 log₁₀ cfu/mL, reaching a sensitivity of 73.5% (95% CI: 55.6, 87.1) and a specificity of 87.5% (95% CI: 71.0, 96.5). Overall, the results of this study indicated that RRT was affected by the intramammary challenge with Strep. uberis and the RRT-generated alerts had similar accuracy as reported for other sensors and algorithms. Further research that includes natural infections with other pathogens as well as different variations in RRT to determine CM status is warranted.

A genomic assessment of the correlation between milk production traits and claw and udder health traits in Holstein dairy cattle

Claw diseases and mastitis represent the most important disease traits in dairy cattle with increasing incidences and a frequently mentioned connection to milk yield. Yet, many studies aimed to detect the genetic background of both trait complexes via fine-mapping of quantitative trait loci. However, little is known about genomic regions that simultaneously affect milk production and disease traits. For this purpose, several tools to detect local genetic correlations have been developed. In this study, we attempted a detailed analysis of milk production and disease traits as well as their interrelationship using a sample of 34,497 50K genotyped German Holstein cows with milk production and claw and udder disease traits records. We performed a pedigree-based quantitative genetic analysis to estimate heritabilities and genetic correlations. Additionally, we generated GWAS summary statistics, paying special attention to genomic inflation, and used these data to identify shared genomic regions, which affect various trait combinations. The heritability on the liability scale of the disease traits was low, between 0.02 for laminitis and 0.19 for interdigital hyperplasia. The heritabilities for milk production traits were higher (between 0.27 for milk energy yield and 0.48 for fat-protein ratio). Global genetic correlations indicate the shared genetic effect between milk production and disease traits on a whole genome level. Most of these estimates were not significantly different from zero, only mastitis showed a positive one to milk (0.18) and milk energy yield (0.13), as well as a negative one to fat-protein ratio (-0.07). The genomic analysis revealed significant SNPs for milk production traits that were enriched on Bos taurus autosome 5, 6, and 14. For digital dermatitis, we found significant hits, predominantly on Bos taurus autosome 5, 10, 22, and 23, whereas we did not find significantly trait-associated SNPs for the other disease traits. Our results confirm the known genetic background of disease and milk production traits. We further detected 13 regions that harbor strong concordant effects on a trait combination of milk production and disease traits. This detailed investigation of genetic correlations reveals additional knowledge about the localization of regions with shared genetic effects on these trait complexes, which in turn enables a better understanding of the underlying biological pathways and putatively the utilization for a more precise design of breeding schemes.

Retrospective study on bovine clinical mastitis and associated milk loss during the month of its peak occurrence at the National Dairy Farm in the Emirate of Abu Dhabi, United Arab Emirates

Background

Commercial dairy establishments are relatively young in the United Arab Emirates (UAE), and as a result, there is lack of epidemiological data on mastitis in dairy farms.

Methods

A retrospective data of seven years (2015-2021) were used to estimate the cumulative average monthly incidence rate of bovine clinical mastitis and evaluate associated milk loss at the National Dairy Farm. Data were extracted from the records of lactating dairy cows (n = 1300-1450) and analyzed using repeated measure and one-way ANOVA, non-parametric Spearman correlation, paired and unpaired t tests.

Results

The highest average cumulative monthly incidence rate was 49 cases per 1000 cows-year that was recorded in 2019 while the lowest was 19 cases per 1000 cows-year in 2021. The cumulative average monthly incidence rate of clinical mastitis significantly (p < 0.001) varied among the seven years. The cumulative average monthly incidence rate was associated with average monthly humidity (p < 0.01) and average monthly rainfall (p < 0.05); however, it was not associated with the average monthly temperature (p > 0.05). The average daily milk yield of cows with clinical mastitis (Mean ± SEM; 18.6 ± 0.54 kg) was significantly (p < 0.001) lower than the average daily milk yield of clinical mastitis free cows (40.5 ± 0.29 kg). The largest average monthly milk loss due to clinical mastitis was 5% of the average total monthly milk production in 2019 while the lowest was 2% of the average total monthly milk production in 2021.

Conclusion

The result of the study indicated the direct influence of weather conditions such as increased rainfall and humidity, which caused an upsurge in the incidence rate of clinical mastitis, leading to an increased loss in milk and hence the economy of the dairy farm. Proactive preventive measures along with good dairy farm practices that help mitigate the impacts of harsh weather conditions are recommended.

Mastitis: Impact of Dry Period, Pathogens, and Immune Responses on Etiopathogenesis of Disease and its Association with Periparturient Diseases

Mastitis is an inflammation of the mammary gland initiated by pathogenic bacteria. In fact, mastitis is the second most important reason for the culling of cows from dairy herds, after infertility. In this review we focus on various forms of mastitis, including subclinical and clinical mastitis. We also stress the importance of the dry-off period as an important time when pathogenic bacteria might start their insult to the mammary gland. An important part of the review is the negative effects of mastitis on milk production and composition, as well as economic consequences for dairy farms. The two most important groups of bacteria that are involved in infection of the udder, Gram-negative and Gram-positive bacteria, are also discussed. Although all cows have both innate and adaptive immunity against most pathogens, some are more susceptible to the disease than others. That is why we summarize the most important components of innate and adaptive immunity so that the reader understands the specific immune responses of the udder to pathogenic bacteria. One of the most important sections of this review is interrelationship of mastitis with other diseases, especially retained placenta, metritis and endometritis, ketosis, and laminitis. Is mastitis the cause or the consequence of this disease? Finally, the review concludes with treatment and preventive approaches to mastitis.

Antimicrobial use and its association with the presence of methicillin-resistant staphylococci (MRS) and extended-spectrum beta-lactamases (ESBL)-producing coliforms in mastitic milk on dairy farms in the Chiba Prefecture, Japan

Food-producing animals, including dairy cattle, are potential reservoirs of antimicrobial resistance. However, there is limited data on antimicrobial use and the selection of resistant bacteria. Therefore, we investigated the association between antimicrobial use and resistance to mastitis pathogens using 2016 data from milk samples collected from cows with mastitis in 134 dairy farms in Chiba Prefecture, one of the principal dairy production prefectures in Japan. We recorded the antimicrobial use and isolation of methicillin-resistant staphylococci (MRS) and extended-spectrum beta-lactamase (ESBL)-producing coliforms (E. coli and Klebsiella spp.), and used the antimicrobial treatment incidence (ATI; the theoretical number of animals per 1000 animal-days subjected to antimicrobial treatment) to indicate antimicrobial use on each farm. The farms in which MRS or ESBL-producing coliforms were isolated from at least one mastitic milk sample were classified as antimicrobial resistance (AMR)-positive, and those in which neither MRS nor ESBL-producing coliforms were isolated were classified as AMR-negative. The AMR-positive farms showed a significantly higher ATI (median 45.17) than AMR-negative farms (median 38.40). The results indicate that high antimicrobial usage is associated with AMR in staphylococci and coliforms isolated from mastitic milk on dairy farms in Chiba Prefecture.

A longitudinal census of the bacterial community in raw milk correlated with Staphylococcus aureus clinical mastitis infections in dairy cattle

BACKGROUND

Staphylococcus aureus is a common cause of clinical mastitis (CM) in dairy cattle. Optimizing the bovine mammary gland microbiota to resist S. aureus colonization is a growing area of research. However, the details of the interbacterial interactions between S. aureus and commensal bacteria, which would be required to manipulate the microbiome to resist infection, are still unknown. This study aims to characterize changes in the bovine milk bacterial community before, during, and after S. aureus CM and to compare bacterial communities present in milk between infected and healthy quarters.

METHODS

We collected quarter-level milk samples from 698 Holstein dairy cows over an entire lactation. A total of 11 quarters from 10 cows were affected by S. aureus CM and milk samples from these 10 cows (n = 583) regardless of health status were analyzed by performing 16S rRNA gene amplicon sequencing.

RESULTS

The milk microbiota of healthy quarters was distinguishable from that of S. aureus CM quarters two weeks before CM diagnosis via visual inspection. Microbial network analysis showed that 11 OTUs had negative associations with OTU0001 (Staphylococcus). A low diversity or dysbiotic milk microbiome did not necessarily correlate with increased inflammation. Specifically, Staphylococcus xylosus, Staphylococcus epidermidis, and Aerococcus urinaeequi were each abundant in milk from the quarters with low levels of inflammation.

CONCLUSION

Our results show that the udder microbiome is highly dynamic, yet a change in the abundance in certain bacteria can be a potential indicator of future S. aureus CM. This study has identified potential prophylactic bacterial species that could act as a barrier against S. aureus colonization and prevent future instances of S. aureus CM.

Risk factors associated with the bovine subclinical mastitis in an Amazon micro-region

In this study, we evaluated the main risk factors for the occurrence of bovine mastitis, in the southeastern of Pará, in the Brazilian Amazon. We surveyed 91 dairy farmers to identify management practices and bovine breed characteristics. From each farm, 50 mL of milk sample was collected for microbiological analysis and somatic cell count (SCC). Depending on the management practices and breed, a logit model was used to determine the odds ratio of subclinical mastitis (SCM) occurrence. In irrigated pastures, an SCM-associated risk factor, the occurrence of SCM was 5.03 times higher than that in the non-irrigated pastures. Similarly, in Girolando breed herds, the occurrence of SCM increased by 5.8 times compared to the crossbred herds. Moreover, the occurrence of mastitis was 33 times higher in farms using common cloths for drying teats than in farms using paper towels. Therefore, adoption of better management practices can lead to SCC reduction, milk quality improvement and a guarantee to contain SCC within prescribed Brazilian limits for the Amazon region.

Mastitis: What It Is, Current Diagnostics, and the Potential of Metabolomics to Identify New Predictive Biomarkers

Periparturient diseases continue to be the greatest challenge to both farmers and dairy cows. They are associated with a decrease in productivity, lower profitability, and a negative impact on cows’ health as well as public health. This review article discusses the pathophysiology and diagnostic opportunities of mastitis, the most common disease of dairy cows. To better understand the disease, we dive deep into the causative agents, traditional paradigms, and the use of new technologies for diagnosis, treatment, and prevention of mastitis. This paper takes a systems biology approach by highlighting the relationship of mastitis with other diseases and introduces the use of omics sciences, specifically metabolomics and its analytical techniques. Concluding, this review is backed up by multiple studies that show how earlier identification of mastitis through predictive biomarkers can benefit the dairy industry and improve the overall animal health.

Mastitis in cattle due to Mycobacteroides abscessus - case report

ABSTRACT Mastitis is considered the main disease that affects dairy cattle worldwide, and it is caused mainly by Staphylococcus aureus and environmental Streptococcus spp. Eventually, nonconventional pathogens, as rapidly growing mycobacteria(RGM), may also cause chronic mastitis, which will not be responsive to antibiotic treatments. Diagnosis of mastitis caused by RGM is a difficult task, and most of time this agent may be misdiagnosed. Here we describe a case of clinical mastitis caused by the RGM Mycobacteroides abscessus in a cow from Southern Brazil, confirmed by microbiological and molecular characterization. Our results reinforce the necessity of a detailed laboratorial identification of the agent and to include this agent in differential diagnosis of chronical clinical mastitis nonresponsive to treatment.

Factors Associated with the Severity of Clinical Mastitis

Severe mastitis can lead to considerable disturbances in the cows’ general condition and even to septicemia and death. The aim of this cross-sectional study was to identify factors associated with the severity of the clinical expression of mastitis. Streptococcus (Str.) uberis (29.9%) was the most frequently isolated pathogen, followed by coliform bacteria (22.3%). The majority of all mastitis cases (n = 854) in this study were either mild or moderate, but 21.1% were severe. It can be deduced that the combination of coliform pathogens and increasing pathogen shedding of these showed associations with severe mastitis. Furthermore, animal-related factors associated with severe disease progression were stages of lactation, and previous diseases in the period prior to the mastitis episode. Cows in early lactation had more severe mastitis. Ketosis and uterine diseases in temporal relation to the mastitis were associated with more severe mastitis in the diseased cows. Hypocalcemia was significantly associated with milder mastitis. As another factor, treatment with corticosteroids within two weeks before mastitis was associated with higher severity of mastitis. Knowledge of these risk factors may provide the basis for randomized controlled trials of the exact influence of these on the severity of mastitis.

Invited review: Selective use of antimicrobials in dairy cattle at drying-off

Administering intramammary antimicrobials to all mammary quarters of dairy cows at drying-off [i.e., blanket dry cow therapy (BDCT)] has been a mainstay of mastitis prevention and control. However, as udder health has considerably improved over recent decades with reductions in intramammary infection prevalence at drying-off and the introduction of teat sealants, BDCT may no longer be necessary on all dairy farms, thereby supporting antimicrobial stewardship efforts. This narrative review summarizes available literature regarding current dry cow therapy practices and associated impacts of selective dry cow therapy (SDCT) on udder health, milk production, economics, antimicrobial use, and antimicrobial resistance. Various methods to identify infections at drying-off that could benefit from antimicrobial treatment are described for selecting cows or mammary quarters for treatment, including utilizing somatic cell count thresholds, pathogen identification, previous clinical mastitis history, or a combination of criteria. Selection methods may be enacted at the herd, cow, or quarter levels. Producers' and veterinarians' motivations for antimicrobial use are discussed. Based on review findings, SDCT can be adopted without negative consequences for udder health and milk production, and concurrent teat sealant use is recommended, especially in udder quarters receiving no intramammary antimicrobials. Furthermore, herd selection should be considered for SDCT implementation in addition to cow or quarter selection, as BDCT may still be temporarily necessary in some herds for optimal mastitis control. Costs and benefits of SDCT vary among herds, whereas impacts on antimicrobial resistance remain unclear. In summary, SDCT is a viable management option for maintaining udder health and milk production while improving antimicrobial stewardship in the dairy industry.

Prevalence, Diagnosis and Improving the Effectiveness of Therapy of Mastitis in Cows of Dairy Farms in East Kazakhstan

In the present work, the prevalence, etiological factors and effective treatment scheme of mastitis in cows of dairy farms “Balke” and “Madi-R” in Eastern Kazakhstan were investigated. In total, 210 heads were investigated on two farms. The incidence of mastitis in cows on dairy farms is not the same in different years. Average clinical mastitis was detected in 35.4% of cows in 2016, 19.6% in 2017, 28.5% in 2018, and in 2019 in 16.4% of cows. The prevalence rates of subclinical mastitis by year had some differences. So, in 2016—36.5% of cows, then in 2017—21.5%, 2018—19.3% and in 2019—22.6%. In cows with udder inflammation, serum calcium 9.37 ± 0.15 mg/% with a range of 8.0 to 10.8 mg/%, phosphorus 3.58 ± 0.07 mg/% (3.0 to 4.3 mg/%), reserve alkalinity 363.46 ± 6.69 mg/% (320 to 440), carotene 0.49 ± 0.03 mg/% (0.220 to 0.988 mg/%), which are in the lower limit of physiological parameters. The drug “Dorob” was tested during the study of comparative effectiveness of treatment methods. The results of the study showed that this drug has anti-inflammatory, antimicrobial and stimulating healing actions. The treatment of the sick cows with catarrhal mastitis has shown that a total of 8 cows have recovered in the control group and 10 cows in the experimental group with the preparation “Dorob”. The period of recovery in the control group was 8.8 ± 0.39, and in the experimental group—6.2 ± 0.28 (p < 0.05). The drug does not contain antibiotics and hormonal preparations. The inclusion of the drug in the scheme of treatment allows for effectively treating inflammatory processes in the udder of cows and restoring their productivity with minimal cost of time and money.

The Dissemination of a Single Staphylococcusaureus Strain, Spa-t2873, as the Predominant Cause of Bovine Mastitis in Israeli Dairy Farms

Simple Summary

Staphylococcus aureus is one of the most important pathogens causing intramammary infection (IMI) in cattle. We aimed to characterize which are the specific strains that are responsible for the majority of these cases. During the one-year survey, S. aureus was identified in 152 dairy farms, with a total of 440 positive samples. One specific type (designated-spa t2873) was found in 284 isolates (64.5%). Notably, 25 cases were detected in one specific farm, all of which were found to be dominant spa t2873 type. By using genomic analysis, we were able to ascertain that most transmission events occurred within the same milking group. Our study revealed the dissemination of a single strain to the majority of Israeli dairy farms. The possibility of inter-farm transmission should be monitored and prevented.

Abstract

Staphylococcus aureus is one of the most important pathogens causing intramammary infection (IMI) in dairy herds. The goals of this study were (1) to describe the prevalence of S. aureus in Israeli dairy farms; (2) to characterize the spa-based clonal structure of mastitis-related S. aureus isolates; (3) to analyze the transmission network of a large outbreak within a single farm and (4) to characterize the virulence factors of the outbreak strain. The prevalence and the molecular survey were performed on all Israeli IMI-related isolates, 9.2019–8.2020. Molecular methods included spa-typing for the survey and whole-genome sequencing (WGS) for the investigation of the farm ‘A’ outbreak. During the one-year survey, S. aureus was identified in 152 dairy farms, with a total of 440 positive samples. The spa t2873 was found in 284 isolates (64.5%) across 112 farms (73.6%). Other common types included t529 (n = 46), t9303 (n = 34) and the methicillin-resistant S. aureus t011 (n = 11). The highest number of cases (n = 25) was detected in Farm ‘A’, all of which were found to be spa t2873. Phylogenetic analysis confirmed that most transmission events occurred within the same milking group, and inter-group transmission was due to the transfer of cows between groups or due to consecutive milking order. The spa t2873 strain contained putative virulence genes, including various intracellular and collagen adhesion proteins. Our study revealed the dissemination of the t2873 strain to the majority of Israeli dairy farms. The possibility of inter-farm transmission should be monitored and prevented.

The Prevalence of Klebsiella spp. Associated With Bovine Mastitis in China and Its Antimicrobial Resistance Rate: A Meta-Analysis

Understanding distribution of bovine mastitis pathogen Klebsiella spp. can contribute to the treatment decision and the control within programs of bovine mastitis, we conducted a meta-analysis to investigate the epidemiology and antimicrobial resistance rates of Klebsiella spp. associated with bovine mastitis in China. Three databases, namely, PubMed, Google scholar, and China National Knowledge Infrastructure database, were utilized to obtain relevant publications. According to PRISMA reporting standards, a total of 38 publications were included in the research, among them, 7 papers included an AMR test. The pooled prevalence of Klebsiella spp. was 5.41% (95% CI: 3.87–7.50%). Subgroup analysis revealed that the prevalence was higher in South China (8.55%, 95% CI: 3.57–19.09%) than in North China (4.22%, 95% CI: 2.46–7.14%), in 2010–2020 (7.45%, 95% CI: 5.29–110.40%) than in 2000–2010 (3.14%, 95% CI: 1.90–15.14%), and in the clinical bovine mastitis cases (7.49%, 95% CI: 3.71–14.54%) than in the subclinical cases (4.03%, 95% CI: 1.55–10.08%). The pooled AMR rate revealed that Klebsiella spp. were most resistant to sulfonamides (45.07%, 95% CI: 27.72–63.71%), followed by tetracyclines (36.18%, 95% CI: 23.36–51.34%), aminoglycosides (27.47%, 95% CI: 17.16–40.92%), β-lactams (27.35%, 95% CI: 16.90–41.05%), amphenicol (26.82%, 95% CI: 14.17–44.87%), lincosamides (21.24%, 95% CI: 7.65–46.75%), macrolides (20.98%, 95% CI: 7.20–47.58%), polypeptides (15.51%, 95% CI: 6.46–32.78%), and quinolones (7.8%, 95% CI: 3.25–17.56%). The climate difference between South and North China and the natural pathogenicity of Klebsiella spp. may be the primary reasons for its distribution, and the prevalence of Klebsiella spp. indicated that the genus is an increasing hazard to the dairy industry. The prevalence of AMR in China is commonly higher than in the European countries and Canada, this is a very important concern for strategy programs to control bovine mastitis caused by Klebsiella spp. in China.

nor 3′-Demethoxyisoguaiacin from Larrea tridentata Is a Potential Alternative against Multidrug-Resistant Bacteria Associated with Bovine Mastitis

Bovine mastitis is one of the most common diseases in dairy cows, and it causes significant economic losses in dairy industries worldwide. Gram-positive and Gram-negative bacteria can cause bovine mastitis, and many of them have developed antimicrobial resistance. There is an urgent need for novel therapeutic options to treat the disease. Larrea tridentata-derived compounds represent an important potential alternative treatment. The aim of the present study was to isolate and characterize antibacterial compounds from Larrea tridentata against multidrug-resistant bacteria associated with bovine mastitis. The L. tridentata hydroalcoholic extract (LTHE) exhibited antibacterial activity. The extract was subjected to a bipartition, giving an aqueous fraction (moderate antibacterial activity) and an organic fraction (higher antibacterial activity). Chromatographic separation of the organic fraction enabled us to obtain four active sub-fractions. Chemical analyses through HPLC techniques were conducted for the LTHE, fractions, and sub-fraction Ltc1-F3, from which we isolated two compounds, characterized by ¹H and ¹³C NMR analyses. Compound nor-3 demethoxyisoguaiacin exhibited the best antibacterial activity against the evaluated bacteria (MIC: 0.01–3.12 mg/mL; MBC: 0.02–3.12 mg/mL). The results indicated that nor-3 demethoxyisoguaiacin can be used as an alternative treatment for multidrug-resistant bacteria associated with mastitis.

Proteomic Comparison of Ivermectin Sensitive and Resistant Staphylococcus aureus Clinical Isolates Reveals Key Efflux Pumps as Possible Resistance Determinants

Ivermectin (IVM) is a versatile drug used against many microorganisms. Staphylococcus aureus is one of the most devastating microorganisms. IVM sensitive and resistant S. aureus strains were recently reported. However, the underlying molecular mechanisms of resistance are unknown. Clinical isolates of S. aureus were used for determination of the sensitivities against IVM by growth curve analysis and time-kill kinetics. Then, proteomic, and biochemical approaches were applied to investigate the possible mechanisms of resistance. Proteomic results showed a total of 1849 proteins in the dataset for both strains, 425 unique proteins in strain O9 (IVM sensitive), and 354 unique proteins in strain O20 (IVM resistant). Eight proteins with transport functions were differentially expressed in the IVM resistant strain. Among them, three efflux pumps (mepA, emrB, and swrC) were confirmed by qPCR. The IVM resistant S. aureus may overexpress these proteins as a key resistance determinant. Further experiments are required to confirm the exact mechanistic relationship. Nevertheless, the possibility of blocking these transporters to reverse or delay the onset of resistance and reduce selection pressure is potentially appealing.

Antioxidants Attenuate Heat Shock Induced Premature Senescence of Bovine Mesenchymal Stem Cells

Mesenchymal stem cells (MSC) have many roles that are important for the body's proper functioning. When the MSC pool is damaged, it is often correlated with impaired development or health of the organism. MSC are known for their anti-inflammatory, immunomodulatory and trophic characteristics that play an important role in the physiological homeostasis of many tissues. Heat shock impairs MSC capacity by inducing the generation of reactive oxygen species and mitochondrial dysfunction, which, in turn, send the cells into a state of premature senescence. Here, we pre-exposed MSC to melatonin, resveratrol, or curcumin, which are natural antioxidative compounds, and tested the protective effects of these substances from oxidative stress and aging. Our data showed that pre-exposure of MSC to antioxidants decreased reactive oxygen species while mitochondrial damage remained high. Additionally, although the proliferation of the cells was slow, antioxidants protected the cells from premature senescence, and subsequent cytokine release was prevented. We conclude that while elevated temperatures directly cause mitochondrial damage, senescence is induced by elevated ROS levels. We suggest that heat shock alters cell and tissue homeostasis by several independent mechanisms; however, reducing tissue senescence will reduce damage and provide a pathway to overcome physiological challenges in animals.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): antimicrobial-resistant Staphylococcus aureus in cattle and horses

Staphylococcus aureus (S. aureus) was identified among the most relevant antimicrobial-resistant (AMR) bacteria in the EU for cattle and horses in previous scientific opinions. Thus, it has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on its eligibility to be listed, Annex IV for its categorisation according to disease prevention and control rules as in Article 9, and Article 8 for listing animal species related to the bacterium. The assessment has been performed following a methodology previously published. The outcome is the median of the probability ranges provided by the experts, which indicates whether each criterion is fulfilled (lower bound ≥ 66%) or not (upper bound ≤ 33%), or whether there is uncertainty about fulfilment. Reasoning points are reported for criteria with uncertain outcome. According to the assessment here performed, it is uncertain whether AMR S. aureus can be considered eligible to be listed for Union intervention according to Article 5 of the AHL (60-90% probability). According to the criteria in Annex IV, for the purpose of categorisation related to the level of prevention and control as in Article 9 of the AHL, the AHAW Panel concluded that the bacterium does not meet the criteria in Sections 1, 2 and 4 (Categories A, B and D; 1-5%, 5-10% and 10-33% probability of meeting the criteria, respectively) and the AHAW Panel was uncertain whether it meets the criteria in Sections 3 and 5 (Categories C and E, 33-90% and 60-90% probability of meeting the criteria, respectively). The animal species to be listed for AMR S. aureus according to Article 8 criteria include mainly mammals, birds, reptiles and fish.

Values and Risk Perception Shape Canadian Dairy Farmers' Attitudes toward Prudent Use of Antimicrobials

Antimicrobial resistance (AMR) is an important challenge in public health. Ensuring rational antimicrobial use (AMU) on farms is one of the key components of antimicrobial stewardship. We aimed to describe a sample of Canadian dairy farmers' personal factors for AMUand their AMR risk perception, and to associate these factors with their attitude toward promotion of prudent AMU. We distributed an online survey among dairy farmers in Ontario and Atlantic Canada (New Brunswick, Nova Scotia, and Prince Edward Island). The questionnaire was designed to solicit information on dairy farmers' AMU decision-making process, attitudes toward AMU reduction, awareness of AMR, and individual values. We performed a factor analysis on 15 statements related to AMR awareness and AMU reduction and used a logistic regression model to identify variables associated with the probability of disagreeing with the need to increase promotion of responsible AMU in the dairy industry. Respondents' (n = 193) previous experience was the main reason to select an antimicrobial treatment for their cattle. We identified four groups of factors related to knowledge, risk perception, and emotional states among respondents. To the question "Should there be more initiatives to promote responsible use of antibiotics in the dairy industry?" 23% of respondents answered no, which was associated in a logistic regression model with being a farm owner, having a tie-stall barn, and considering their own experience as the most important factor in selecting antimicrobial treatments. The score for the conservation value dimension and score for a factor described as sense of responsibility when using antimicrobials were also retained in the final model. Our results indicate that tailored strategies to promote prudent AMU on dairy farms may be preferable to a generic strategy because there are individual differences in attitudes, values, and AMR awareness that shape AMR risk perception and willingness to modify current AMU practices.

First test-day postcalving risk factors for clinical mastitis in southern Chile dairy farms: A retrospective cohort study

We conducted a retrospective cohort study to evaluate risk factors associated with clinical mastitis in dairy cows in southern Chile between the first milk test after calving to 200 d in milk (DIM). Data from 8,772 cows were collected from June 2017 to November 2019 on 10 dairy farms selected by convenience in southern Chile. Data were analyzed using a multivariable mixed logistic regression using a manual backward selection process with logit link function and farm as a random effect. The dependent variable was clinical mastitis between the first milking sample collected by monthly milk sampling program up to 200 DIM. Days in milk, fat, urea, parity, season, and somatic cell counts were statistically associated with clinical mastitis in the first 200 d in milk. Cows with higher than average milk yield, parity, urea, and somatic cell count were at greater odds of being diagnosed with clinical mastitis compared with their respective referents. In contrast, higher milk fat was associated with lower odds of clinical mastitis. Significant interactions between days in milk with season and parity were observed, where for every 5-d increase in DIM, the odds of clinical mastitis decreased by different proportions depending on the interaction. Identified risk factors for clinical mastitis using first monthly milk sampling data can help dairy farmers in Chile implement herd-level mastitis prevention and control measures.