Expression profile of genes associated with mastitis in dairy cattle

Effects of Temperature and Time on the Denaturation of Transforming Growth Factor Beta-1 and Cytokines from Bovine Platelet-Rich Gel Supernatants

There is a lack of information about transforming growth factor beta-1 (TGF-β1) and cytokines contained in pure platelet-rich plasma (P-PRP) and release from pure-platelet-rich gel supernatants (P-PRGS) might be affected by the temperature and time factors; P-PRP from 6 heifers was activated with calcium gluconate. Thereafter, P-PRG and their supernatants (P-PRGS) were maintained at -80, -20, 4, 21, and 37 °C and collected at 3, 6, 12, 24, 48, 96, 144, 192, 240, and 280 h for subsequent determination of TGF-β1, tumor necrosis factor alfa (TNF-α), interleukin (IL)-2, and IL-6; TGF-β1 concentrations were significantly (p < 0.05) higher in PRGS maintained at 21 and 37 °C when compared to PRGS maintained at 4, -20, and -80 °C; PRGS TNF-α concentrations were not influenced by temperature and time factors. However, PRGS maintained at 4 °C showed significantly (p < 0.05) higher concentrations when compared to PRGS maintained at -20, and -80 °C at 144, and 192 h. IL-6 concentrations were significantly (p < 0.05) higher in PRGS stored at -20, and -80 over the first 48 h and at 10 days when compared to PRGS stored at 4, 21, and 37 °C. These results could suggest that P-PRP/P-PRGS could be maintained and well preserved for at least 12 days at room temperature for clinical use in bovine therapeutic massive protocols.

Methylation Levels in the Promoter Region of FHIT and PIAS1 Genes Associated with Mastitis Resistance in Xinjiang Brown Cattle

Mastitis causes serious economic losses in the dairy industry, but there are no effective treatments or preventive measures. In this study, the ZRANB3, PIAS1, ACTR3, LPCAT2, MGAT5, and SLC37A2 genes in Xinjiang brown cattle, which are associated with mastitis resistance, were identified using a GWAS. Pyrosequencing analysis showed that the promoter methylation levels of the FHIT and PIAS1 genes in the mastitis group were higher and lower, respectively, than those in the healthy group (65.97 ± 19.82% and 58.00 ± 23.52%). However, the methylation level of the PIAS1 gene promoter region in the mastitis group was lower than that in the healthy group (11.48 ± 4.12% and 12.17 ± 4.25%). Meanwhile, the methylation levels of CpG3, CpG5, CpG8, and CpG15 in the promoter region of the FHIT and PIAS1 genes in the mastitis group were significantly higher than those in the healthy group (p < 0.01), respectively. RT-qPCR showed that the expression levels of the FHIT and PIAS1 genes were significantly higher in the healthy group than those in the mastitis group (p < 0.01). Correlation analysis showed that the promoter methylation level of the FHIT gene was negatively correlated with its expression. Hence, increased methylation in the promoter of the FHIT gene reduces the mastitis resistance in Xinjiang brown cattle. Finally, this study provides a reference for the molecular-marker-assisted selection of mastitis resistance in dairy cattle.

Candidate genes for mastitis resistance in dairy cattle: a data integration approach

BACKGROUND

Inflammation of the mammary tissue (mastitis) is one of the most detrimental health conditions in dairy ruminants and is considered the most economically important infectious disease of the dairy sector. Improving mastitis resistance is becoming an important goal in dairy ruminant breeding programmes. However, mastitis resistance is a complex trait and identification of mastitis-associated alleles in livestock is difficult. Currently, the only applicable approach to identify candidate loci for complex traits in large farm animals is to combine different information that supports the functionality of the identified genomic regions with respect to a complex trait.

METHODS

To identify the most promising candidate loci for mastitis resistance we integrated heterogeneous data from multiple sources and compiled the information into a comprehensive database of mastitis-associated candidate loci. Mastitis-associated candidate genes reported in association, expression, and mouse model studies were collected by searching the relevant literature and databases. The collected data were integrated into a single database, screened for overlaps, and used for gene set enrichment analysis.

RESULTS

The database contains candidate genes from association and expression studies and relevant transgenic mouse models. The 2448 collected candidate loci are evenly distributed across bovine chromosomes. Data integration and analysis revealed overlaps between different studies and/or with mastitis-associated QTL, revealing promising candidate genes for mastitis resistance.

CONCLUSION

Mastitis resistance is a complex trait influenced by numerous alleles. Based on the number of independent studies, we were able to prioritise candidate genes and propose a list of the 22 most promising. To our knowledge this is the most comprehensive database of mastitis associated candidate genes and could be helpful in selecting genes for functional validation studies.

Analysis of runs of homozygosity of cattle living in different climate zones

Aim of this study was to analyze the distribution and characteristics of runs of homozygosity in Bos taurus taurus and Bos taurus indicus breeds, as well as their crosses, farmed all around the world. With this aim in view, we used single-nucleotide polymorphisms (SNP) genotypes for 3,263 cattle belonging to 204 different breeds. After quality control, 23,311 SNPs were retained for the analysis. Animals were divided into seven different groups: 1) continental taurus, 2) temperate taurus, 3) temperate indicus, 4) temperate composite, 5) tropical taurus, 6) tropical indicus, and 7) tropical composite. The climatic zones were created according to the latitude of the breeds' country of origin: i) continental, latitude ≥ 45°; ii) temperate, 45°< Latitude >23.26°; iii) tropics, latitude ≤ 23.26°. Runs of homozygosity were computed as 15 SNPs spanning in at least 2 Mb; number of ROH per animal (nROH), average ROH length (meanMb), and ROH-based inbreeding coefficients (FROH) were also computed. Temperate indicus showed the largest nROH, whereas Temperate taurus the lowest value. Moreover, the largest meanMb was observed for Temperate taurus, whereas the lowest value for Tropics indicus. Temperate indicus breeds showed the largest FROH values. Genes mapped in the identified ROH were reported to be associated with the environmental adaptation, disease resistance, coat color determinism, and production traits. Results of the present study confirmed that runs of homozygosity could be used to identify genomic signatures due to both artificial and natural selection.

Gene expression adjustment of inflammatory mechanisms in dairy cow mammary gland parenchyma during host defense against staphylococci

The aim of the study was to identify differences in the expression of splice variants of the PRMT2, LTF and C4A genes in the mammary glands of healthy dairy cows and those infected with staphylococci. An expression study was conducted on 38 Polish Holstein-Friesian dairy cows who were removed from the herd owing to subclinical and chronic mastitic or reproductive issues. Two days before slaughter, milk samples were taken for microbiological analysis and examined for the presence of bacteria. The mammary gland parenchyma samples with a predominance of secretory tissue were taken; these were divided into three groups according to the health status of the mammary gland: H (without pathogenic bacteria in milk), CoNS (with coagulase-negative staphylococci in milk), and CoPS (with coagulase-positive staphylococci in milk). Two of the investigated genes, LTF and C4A, demonstrated variants unequivocally expressed in infected tissue. Two LTF gene variants were found to be associated with cow health status, and with the type of bacteria causing mastitis (CoPS or CoNS). In addition, the expression of C4A isoforms differed with regard to mastitis etiology groups. The comprehensive evaluation of PRMT2 transcript suggested that the gene may also be involved in course of mastitis: two of four PRMT2 transcripts showed increased expression in the mammary gland of the CoPS group compared to controls. The obtained results are important for the knowledge on the etiology of bovine mastitis. The effects of the identified mastitis-relevant splice variants need to be further explored on the protein level to verify the suitability of splice variants and recognize their contribution towards the disease phenotypes and course.

Identification of Inflammatory and Regulatory Cytokines IL-1α-, IL-4-, IL-6-, IL-12-, IL-13-, IL-17A-, TNF-α-, and IFN-γ-Producing Cells in the Milk of Dairy Cows with Subclinical and Clinical Mastitis

In naturally occurring bovine mastitis, effects of infection depend on the host inflammatory response, including the effects of secreted cytokines. Knowledge about the inflammatory and regulatory cytokines in milk cells of free-stall barn dairy cows and in naturally occurring mastitis is lacking as most studies focus on induced mastitis. Hereby, the aim of the study was to determine inflammatory and regulatory cytokines in the milk of dairy cows with subclinical and clinical mastitis. The following examinations of milk samples were performed: differential counting of somatic cells (SCC), bacteriological examination, and immunocytochemical analysis. Mean SCC increased in subclinical and clinical mastitis cases. The number of pathogenic mastitis-causing bacteria on plates increased in subclinical mastitis cases but decreased in clinical mastitis. The inflammatory and regulatory markers in the milk cells of healthy cows showed the highest mean cell numbers (%). In mastitis cases, immunoreactivity was more pronounced for IL-4, IL-6, IL-12, IL-13, IL-17A, TNF-α, and IFN-γ. Data about subclinical and clinical mastitis demonstrate inflammatory responses to intramammary infection driven by IL-1α, IL-4, and IL-17A. Moreover, the host defense response in mastitis is characterized by continuation or resolution of initial inflammation. IL-12 and INF-γ immunoreactivity was recognized to differ mastitis cases from the relative health status.

Expression analysis of candidate genes for chronic subclinical mastitis in Norwegian Red cattle

Chronic subclinical mastitis (SCM) is characterized by a long-term inflammation in the udder with high somatic cell count (SCC) in milk. Previously, several novel alternative SCM traits for Norwegian Red (NR) cattle have been defined to improve breeding strategies against chronic SCM. Quantitative trait loci and candidate genes affecting chronic SCM in NR have been identified. The aim of this study was to analyze the expression profiles of 14 selected candidate genes (RAD17, ACOT2, ACOT4, FOS, CXCL1, CXCL8, CCNB1, CDK7, TGFB3, SEL1L, STAT4, C6, GLI2, and SLC18A2). Twenty healthy NR cows with official genomic estimated breeding values (GEBV) for lactation average somatic cell scores (LSCS) were selected. Ten cows had high GEBV for LSCS (cows with low probability to have high SCC in milk during lactation) and 10 cows had low GEBV for LSCS (cows with high probability of having high SCC in milk). We isolated RNA from unstimulated peripheral blood mononuclear cells from these. Two out of the 14 analyzed genes showed significantly different results between groups. The group with high GEBV for LSCS displayed significantly higher expression of the CXCL1 gene than the low GEBV group. Grouping by lactation stage revealed significant differential expression of the FOS gene, with higher expression in early lactation (2-3 mo after calving) compared with late lactation (7-8 mo after calving). In addition, flow cytometry was performed on the peripheral blood mononuclear cells samples to analyze if number and type of isolated cells influenced the gene expression in the groups. The results in the current study provide identified genes that can be considered as possible candidate genes for chronic SCM in NR cows.

Polymorphisms in JAK2 Gene are Associated with Production Traits and Mastitis Resistance in Dairy Cattle

The present study was designed to investigate the effects of single nucleotide polymorphisms (SNPs) in the JAK2 gene on the production and mastitis related traits in dairy cattle. Blood and milk samples were collected from 201 lactating dairy cattle of three breeds, i.e. Holstein Friesian (HF), Jersey (J) and Achai (A) and their crosses maintained at well-established dairy farms in Khyber Pakhtunkhwa, Pakistan. Generalized linear model was used to evaluate the association between genotypes and the studied traits. A DNA pool was made from randomly selected 30 samples which revealed three SNPs, i.e. SNP 1 in 5’ upstream region (G>A, rs379754157), SNP 2 in intron 15 (A>G, rs134192265), and SNP 3 in exon 20 (A>G, rs110298451) that were further validated in the population under study using SNaPshot technique. Of the three SNPs, SNP 1 did not obey Hardy-Weinberg equilibrium (P<0.05). SNP 2 and SNP 3 were found to be in strong linkage disequilibrium and allele G was highly prevalent compared to allele A in these SNPs. in SNP 1, the GG genotype was associated with significantly (P<0.01) higher SCC, whereas SNP 2 and SNP 3 were significantly (P<0.01) associated with higher lactose percentage compared to the other geno-types. The haplogroups association analysis revealed that H1H2 (GG GG AG) has significantly lower SCC than H2H2 (GG GG GG). The results infer that JAK2 could be an important candidate gene and the studied SNPs might be useful genetic markers for production and mastitis related traits.

Potential roles of neutrophils in maintaining the health and productivity of dairy cows during various physiological and physiopathological conditions: a review

Neutrophils represent the first line of innate immunity and are the most prominent line of cellular defence against invading microorganisms. On stimulation, they can quickly move through the walls of veins and into the tissues of the body to immediately attack or monitor the foreign antigens. Neutrophils are highly versatile and sophisticated cells which are endowed with highly sensitive receptor-based perception systems. They were traditionally classified as short-lived phagocytes actively involved during infection and inflammation, but recently, it has been seen that neutrophils are capable of detecting the presence of sperms during insemination as well as an implanting embryo in the female reproductive tract. These specialised phagocytes play a major role in tissue remodelling and wound healing, and maintain homeostasis during parturition, expulsion of placenta, folliculogenesis, corpus luteum formation and luteolysis. Here, we review the role played by neutrophils in maintaining homeostasis during normal and inflammatory conditions of dairy cattle. We have summarised the alteration in the expression of some cell adhesion molecules and cytokines on bovine neutrophils during different physiological and physiopathological conditions. Some emerging issues in the field of neutrophil biology and the possible strategies to strengthen their activity during the period of immunosuppression have also been discussed.

Transcriptomic analysis on the promoter regions discover gene networks involving mastitis in cattle

Mastitis is one of the costliest diseases in dairy farms caused by infection of different microorganisms such as Escherichia coli, Streptococcus uberis and Staphylococcus aureus. Promoters are significantly involved in regulating gene expression and shedding light on the mechanisms of transcriptional regulation in physiological and immunological processes of the infections. Exploiting regulatory elements such as transcription factor binding sites (TFBSs modules) on the promoter region could reveal co-regulated genes, which allow screating regulatory models and executing a cross-sectional analysis on several databases. In this study, the promoter regions of 11 genes associated with contagious mastitis including CCL4, CXCL8, STAT3, IKBKB, MAPK14, NFKBIA, NFKB1, TNF, IL18, IL6, and HCK were investigated to predict the activating regulatory modules on promoters and to discover the key related transcription factors. By exploring the promoter regions, 228 genes were discovered comprising the same transcription factors modules. Out of 228 genes, 36 were validated using five microarray datasets. The promoter research of these genes revealed that as many as 7 down-regulated and 12 up-regulated genes are predictable in the network. The genes whose functions were associated with the initial gene list (11 genes), were identified by DAVID queries with TFBSs models implying that the approach provides a clear image of the underlying regulatory mechanism of gene expression profile and offers a novel approach in designing gene networks in cattle.

An Investigation on the Expression Level of Interleukin 10 (IL-10) in the Healthy and Mastitic Holstein Cows and the Bioinformatics Analysis of Nucleosome Profile

Cytokines are immune regulators that play an essential role in regulating immune response against various infections. The present study focused on the possible association between the expression level of Interleukin 10 (IL-10) in blood and milk samples of 25 healthy and 25 mastitic cows in Fars province, Iran, using a quantitative real-time PCR assay. The experimental groups were categorized according to the number of calvings. The expression level of IL-10 was significantly higher in the blood and milk samples of mastitic cows compared to the healthy ones. Concomitant to increasing the number of calving, a numerical elevation in the expression of IL-10 in blood was observed (P < 0.05). The bioinformatics analysis of IL-10 gene revealed the promoter, exon-intron regions, and nucleosome profile. The nucleosome occupancy site was finally predicted using NUPOP software. Our result indicated that the promoter was not exactly placed in the nucleosome region, which was finally aimed to predict the position and expression of IL-10 gene in the mastitic cows.

Milk and serum IL-4, IL-6, IL-10, and amyloid A concentrations in cows with subclinical mastitis caused by coagulase-negative staphylococci

The aim of the study was to evaluate the concentrations of cytokines IL-4, IL-6, and IL-10 and acute phase protein amyloid A in milk and in serum from cows with subclinical mastitis caused by coagulase-negative staphylococci and from healthy cows. The blood and milk samples were obtained from 35 midlactation, multiparous (between parities 2 and 4) Holstein-Friesian cows. In the milk samples from 20 cows with subclinical mastitis, the following species of Staphylococcus were detected: Staphylococcus xylosus (8 samples), Staphylococcus chromogenes (6 samples), Staphylococcus haemolyticus (2 samples), Staphylococcus simulans (2 samples), and Staphylococcus sciuri (2 samples). The results of the present study indicate that the level of IL-6 in cows suffering from subclinical mastitis tended to be high in both serum and milk (432.09 and 254.32 pg/mL) compared with the level in healthy cows (164.47 and 13.02 pg/mL, respectively). Amyloid A value also was significantly higher in milk of unhealthy cows compared with cows without subclinical mastitis (790.2 and 360.5 ng/mL). No significant differences were found in levels of amyloid A in serum of both tested groups of cows (2,680.0 and 2,720.0 ng/mL). In contrast, concentration of IL-4 was significantly lower both in serum and in milk of cows with staphylococcal mastitis (86.1 and 123.17 pg/mL) compared with control animals (413.5 and 670.2 pg/mL). The level of IL-10 also was significantly higher in milk of healthy cows than in infected cows (39.78 and 22.5 pg/mL); however, differences in serum levels of this cytokine between tested groups were significantly less important (220.6 and 175.1 pg/mL).

Indirubin Treatment of Lipopolysaccharide-Induced Mastitis in a Mouse Model and Activity in Mouse Mammary Epithelial Cells

Indirubin is a Chinese medicine extracted from indigo and known to be effective for treating chronic myelogenous leukemia, neoplasia, and inflammatory disease. This study evaluated the in vivo anti-inflammatory activity of indirubin in a lipopolysaccharide- (LPS-) induced mouse mastitis model. The indirubin mechanism and targets were evaluated in vitro in mouse mammary epithelial cells. In the mouse model, indirubin significantly attenuated the severity of inflammatory lesions, edema, inflammatory hyperemia, milk stasis and local tissue necrosis, and neutrophil infiltration. Indirubin significantly decreased myeloperoxidase activity and downregulated the production of tumor necrosis factor-α, interleukin-1β (IL-1β), and IL-6 caused by LPS. In vitro, indirubin inhibited LPS-stimulated expression of proinflammatory cytokines in a dose-dependent manner. It also downregulated LPS-induced toll-like receptor 4 (TLR4) expression and inhibited phosphorylation of LPS-induced nuclear transcription factor-kappa B (NF-κB) P65 protein and inhibitor of kappa B. In addition to its effect on the NF-κB signaling pathway, indirubin suppressed the mitogen-activated protein kinase (MAPK) signaling by inhibiting phosphorylation of extracellular signal-regulated kinase (ERK), P38, and c-jun NH2-terminal kinase (JNK). Indirubin improved LPS-induced mouse mastitis by suppressing TLR4 and downstream NF-κB and MAPK pathway inflammatory signals and might be a potential treatment of mastitis and other inflammatory diseases.

Protective effects of kaempferol on lipopolysaccharide-induced mastitis in mice

Kaempferol isolated from the root of Zingiberaceae plants galangal and other Chinese herbal medicines have been reported to have anti-inflammatory properties. However, the anti-inflammatory effects of kaempferol on lipopolysaccharide (LPS)-induced mastitis are unknown and their underlying molecular mechanisms remain to be explored. The aim of this study was to evaluate the effects of kaempferol on LPS-induced mouse mastitis. The mouse model of mastitis was induced by injection of LPS through the duct of mammary gland. Kaempferol was injected 1 h before and 12 h after induction of LPS intraperitoneally. The present results showed that kaempferol markedly reduced infiltration of neutrophilic granulocyte, activation of myeloperoxidase (MPO), expression of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β) in a dose-dependent manner, which were increased in LPS-induced mouse mastitis. Furthermore, kaempferol suppressed the phosphorylation of nuclear factor-κB (NF-κB) p65 subunit and the degradation of its inhibitor IκBα. All results suggest that anti-inflammatory effects of kaempferol against the LPS-induced mastitis possibly through inhibition of the NF-κB signaling pathway. Kaempferol may be a potential therapeutic agent for mastitis.

Genotypic to expression profiling of bovine calcium channel, voltage-dependent, alpha-2/delta subunit 1 gene, and their association with bovine mastitis among Frieswal (HFX Sahiwal) crossbred cattle of Indian origin

Calcium channel, voltage-dependent, alpha-2/delta subunit 1 (CACNA2D1) gene is considered to be an important noncytokine candidate gene influencing mastitis. Scanty of reports are available until today regarding the role play of CACNA2D1 gene on the susceptibility of bovine mastitis. We interrogated the CACNA2D1 G519663A [A>G] SNP by PCR-RFLP among two hundreds Frieswal (HF X Sahiwal) crossbred cattle of Indian origin. Genotypic frequency of AA (51.5, n=101) was comparatively higher than AG (35, n=70) and GG (14.5, n=29). Association of Somatic cell score (SCS) with genotypes revealed that, GG genotypes showing lesser count (less susceptible to mastitis) compare to AA and AG. Relative expression of CACNA2D1 transcript (in milk samples) was significantly higher among GG than AG and AA. Further we have also isolated blood sample from the all groups and PBMCs were cultured from each blood sample as per the standard protocol. They were treated with Calcium channel blocker and the expression level of the CACNA2D1 gene was evaluated by Real Time PCR. Results show that expression level decline in each genotypic group after treatment and expression level of GG are again significantly higher than AA and AG. Thus, it may be concluded that GG genotypic animals are favorable for selecting disease resistant breeds.

Evaluation of internal reference genes for quantitative expression analysis by real-time reverse transcription-PCR in somatic cells from goat milk

Reverse transcription (RT) quantitative real-time PCR (qPCR) is the most accurate and easy-to-perform technique to measure the expression level of a selected gene of interest by quantifying mRNA transcripts. The use of reference genes is commonly accepted as the most reliable approach to normalize RT-qPCR data and reduce possible errors generated in the quantification of gene expression. The optimal number and choice of reference genes are experimentally validated for specific tissues or cell types and experimental designs. To date, data on qPCR normalization in goats are scarce and the most suitable reference genes in this species have been identified for only a limited number of tissues. The aim of this study was to determine an optimal combination of stably expressed reference genes in caprine milk somatic cells (MSC) from healthy and infected mammary glands. For the purpose, we performed RT-qPCR for 10 commonly used reference genes from various functional classes and then determined their expression level in MSC from goats intramammary challenged with Staphylococcus aureus and in MSC from healthy controls, with a view to select genes whose stability would be unaffected under infection conditions. The geNorm and NormFinder algorithms were used for validating the reference genes. Furthermore, to demonstrate the importance of normalization of gene expression with appropriate reference genes, we tested the effect of using a combination of the least stable genes for expression analysis evaluation. On the basis of our evaluation, we recommend the use of a panel of reference genes that should include G6PD, YWHAZ, and ACTB for caprine MSC gene expression profiling. The expression of the 2 genes of interest, pentraxin-related protein (PTX3) and secreted phosphoprotein 1 (SPP1), was evaluated by RT-qPCR in all samples collected pre- and postinfection, and the recommended reference genes were used to normalize the data. Our study provides a validated panel of optimal reference genes for the identification of genes differentially expressed by qRT-PCR in caprine MSC. Moreover, we provided a set of intron-spanning primer sequences that could be suitable for gene expression experiments using SYBR Green chemistry on other caprine tissues and cells.

Effect of somatic cell count and mastitis pathogens on milk composition in Gyr cows

BACKGROUND

Gyr cows are well adapted to tropical conditions, resistant to some tropical diseases and have satisfactory milk production. However, Gyr dairy herds have a high prevalence of subclinical mastitis, which negatively affects their milk yield and composition. The objectives of this study were (i) to evaluate the effects of seasonality, mammary quarter location (rear x front), mastitis-causing pathogen species, and somatic cell count (SCC) on milk composition in Gyr cows with mammary quarters as the experimental units and (ii) to evaluate the effects of seasonality and somatic cell count (SCC) on milk composition in Gyr cows with cows as the experimental units. A total of 221 lactating Gyr cows from three commercial dairy farms were selected for this study. Individual foremilk quarter samples and composite milk samples were collected once a month over one year from all lactating cows for analysis of SCC, milk composition, and bacteriological culture.

RESULTS

Subclinical mastitis reduced lactose, nonfat solids and total solids content, but no difference was found in the protein and fat content between infected and uninfected quarters. Seasonality influenced milk composition both in mammary quarters and composite milk samples. Nevertheless, there was no effect of mammary quarter position on milk composition. Mastitis-causing pathogens affected protein, lactose, nonfat solids, and total solids content, but not milk fat content. Somatic cell count levels affected milk composition in both mammary quarters and composite samples of milk.

CONCLUSIONS

Intramammary infections in Gyr cows alter milk composition; however, the degree of change depends on the mastitis-causing pathogen. Somatic cell count is negatively associated with reduced lactose and nonfat solids content in milk. Seasonality significantly affects milk composition, in which the concentration of lactose, fat, protein, nonfat solids and total solids differs between dry and wet seasons in Gyr cows.

Evaluation of somatic cell count thresholds to detect subclinical mastitis in Gyr cows

The objectives of this study were (1) to determine the sensitivity (Se) and specificity (Sp) of somatic cell count (SCC) thresholds to identify subclinical mastitis in Gyr cows caused by major and minor pathogens; (2) to study the effects of month of sampling, rear or front mammary quarters, herd, intramammary infection (IMI), and bacterial species on SCC at quarter level; and (3) to describe the prevalence of IMI in Gyr cows in commercial dairy herds. In total, 221 lactating Gyr cows from 3 commercial dairy farms were selected. Milk samples were collected from individual quarters once a month for 1 yr from all lactating cows for SCC and bacteriological analysis. Mammary quarters were considered the experimental units and the SCC results were log(10)-transformed. Four SCC thresholds (100, 200, 300 and 400 × 10(3) cells/mL) were used to determine Se and Sp to identify infected mammary quarters. The overall prevalence of IMI in quarter milk samples of Gyr cows was 49.8%, and the prevalence of minor pathogens was higher (31.9%) than that of major pathogens (17.8%). Quarter samples with microbial isolation presented higher SCC compared with negative samples. Sensitivity and Sp of selected SCC thresholds varied according to the group of pathogen (major and minor) involved in the IMI definition. Sensitivity increased and Sp decreased when mammary quarters with only major pathogens isolation were considered positive. The use of a single SCC analysis to classify quarters as uninfected or infected in Gyr cows may not be a useful test for this breed because Se and Sp of SCC at the studied thresholds were low. The occurrence of IMI and the bacterial species are the main factors responsible for SCC variation in mammary quarters of Gyr cows. Milk samples with major pathogens isolation elicited higher SCC than those with minor pathogens.