Udder infection and milk somatic cell count, NAGase activity and milk composition—fat, protein and lactose—in Israeli-Assaf and Awassi sheep

Factors affecting N-acetyl-β-D-glucosaminidase as an indicator for mastitis detection in dairy sheep

The study of new indirect methods for mastitis detection is of great relevance both at the economic level of the farm and dairies, and in terms of consumer health, and animal welfare. These methods help us to monitor the disease and speed up the decision-making process on treatment of the affected animal and the destination of the milk. The main aim of this work was to study the effect of intramammary infection and other non-infectious factors on the activity of the enzyme N-acetyl-β-D-glucosaminidase (NAGase) in milk, in order to evaluate its use as an indicator for the early diagnosis of mastitis in sheep that could be less expensive, easier to measure and a better marker of inflammation or complementary to existing methods such as somatic cell count (SCC). Seven biweekly samplings were carried out, in which NAGase activity, SCC and milk were analyzed. Glands were classified according to their sanitary status based on the results of the SCC and bacteriological analysis. Non-infectious factors such as lactation stage, parity number and milking session had a statistically significant effect on NAGase values, finding the highest NAGase values at the onset and end of the study, in infectious mastitic glands of multiparous females and at morning milking. However, among the NAGase variation factors studied, the health status of the gland was the factor that caused the highest variation in enzyme levels, with infectious mastitic glands showing higher values than healthy glands. The predictive ability of NAGase was also studied by means of several logistic regression models, with the one that included NAGase together with lactation stage and parity obtaining the best results if sensitivity is to be prioritized, or the model that included NAGase, lactation stage, parity, milking and production if specificity is to be prioritized. From the results obtained, it can be concluded that the use of NAGase as an intramammary infection detection method in sheep can be useful when non-infectious factors that cause changes in the concentration of the enzyme are also considered.

Effect of the Onset of Intramammary Infection on the Electrical Conductivity of Ewe's Milk and Study of Various Algorithms for Its On-Line Detection

The aim of this study was to determine the effect of the onset of intramammary infection (IMI) on the electrical conductivity (EC) of ewe milk and assess the detection capability of various algorithms based on daily glandular milk EC measurement. An experiment was carried out with 26 Manchega sheep located at the farm of the Miguel Hernández University, Elche, Spain. The variables in milk from the gland (production, EC) were monitored daily for 2 weeks during the morning and evening milking; once infection was established in the gland, the variables were measured for a further 4 weeks. In addition, the SCC, sodium, potassium, chloride and milk macro-compositions were analysed. The sensitivity, specificity and positive and negative predictive values for IMI detection of different algorithms were calculated using the EC variable. It was observed that the onset of IMI resulted in an increase in SCC and a significant decrease in yield, and EC rose significantly when infection occurred bilaterally. The best results for IMI detection were obtained with the algorithm that detected deviations greater than 3σ of the conductivity ratio between collateral glands with respect to a moving average calculated with a time horizon of 10 days (50% sensitivity and 100% specificity).

The impact of genetic merit on ewe performance and efficiency parameters

The aim of this study was to investigate the impact of ewe genetic merit on ewe performance and efficiency parameters. The study consisted of three genetic merit groups (New Zealand [NZ], High Irish, and Low Irish) and ran from 2016 to 2019, inclusive. Each genetic merit group contained 30 purebred Suffolk and 30 purebred Texel ewes, which were selected based on their maternal genetic indexes in their country of origin, namely Ireland (€uro-star Replacement index) or New Zealand (New Zealand Maternal worth). Ewe body condition score (BCS), ewe body weight (BW), milk yield, milk composition, dry matter intake (DMI), and efficiency parameters were all analyzed using linear mixed models. Ewe BW was similar across all genetic merit groups at each time point (P > 0.05). In comparison to both High and Low Irish ewes, NZ ewes had a higher BCS at mating, mid-pregnancy, lambing, week 10 post-lambing (PL, P < 0.05). Ewe BW change was similar across genetic merit groups, except between mating and mid-pregnancy where ewe BW loss was greater for NZ ewes than Irish ewes (P < 0.05) and between weeks 6 PL and 10 PL, where NZ ewes gained BW and High and Low Irish ewes lost BW (P < 0.01). Ewe milk yield, milk fat, total solids, and gross energy content were superior for milk produced by NZ ewes at week 6 PL in comparison to milk produced by High Irish and Low Irish ewes (P < 0.01). NZ ewes produced a greater quantity of milk solids/kg of BW at week 6 PL compared with High Irish ewes (P < 0.01), whereas Low Irish ewes did not differ from either NZ or High Irish (P > 0.05). Low Irish ewes had a greater daily DMI than High Irish ewes in late lactation (week 10 PL, P < 0.05) and had a greater DMI/kg of ewe BW compared with the High Irish ewes at the same time point (P < 0.05). NZ ewes weaned a litter BW equivalent to 60.4% of their mating BW, which was more than the Low Irish ewes who weaned 57.1% of the ewe's BW at mating (P < 0.01), whereas the High Irish ewes did not differ from either the NZ or Low Irish ewes at 59.3% of the ewe's BW at mating (P > 0.05). This study presents a range of parameters across ewes of high and low genetic merit, demonstrating the ability to achieve gains through selection of animals of high genetic merit. Sheep producers should consider genetic indexes as a tool to assist in the decision-making process of selecting replacement ewes and/or breeding rams, once satisfied the animal is correct, and meeting the breeding objectives of the system.

Effect of Palpable Udder Defects on Milk Yield, Somatic Cell Count, and Milk Composition in Non-Dairy Ewes

In non-dairy ewes, udder defects hinder the survival and weight gain of their pre-weaned lambs. The objectives of this study were to determine the effects of palpable udder defects on milk yield, somatic cell count (SCC), and milk composition in non-dairy Romney ewes. Ewes with a history of udder defects or normal udders were selected for the study. Of a total of 48 ewes that lambed, 30 ewes reared at least one lamb, and were milked six times, once weekly, for the first six weeks of lactation. Udder halves were palpated and scored at each milking event. Multivariate linear mixed models examined the impacts of udder defects on udder-half and whole-udder milk yield, SCC, and milk composition (fat, protein, lactose, total solids, and solids non-fat (SNF)). Across the six examinations, 24.7% of the total 352 udder-half examinations were observed to be defective. Udder halves that were defective at least once produced on average 57.9% less (p < 0.05) milk than normal udder halves, while normal udder halves with a contralateral defective half yielded 33.5% more (p < 0.05) milk than normal udder halves. Successive occurrence of both hard and lump udder defect categories in an udder-half, udder defect detection early in lactation, and a high frequency of udder defect detection were all associated with udder-half milk yield loss (p < 0.05). At the whole-udder level, no differences in milk yield (p > 0.05) were observed between those with one udder-half defective and both normal udder-halves. However, udders in which one udder half was categorised as hard but progressed to lump and remained as lump until 42 days of lactation produced less (p < 0.05) milk compared with normal udders. With the exception of SNF, there were no significant associations (p > 0.05) between milk composition parameters and udder defect. Overall, these findings emphasise the importance of udder health in non-dairy ewes and the potential effect of udder defects on their lambs.

Genome-Wide Association Study Identifies New Candidate Markers for Somatic Cells Score in a Local Dairy Sheep

In the Mediterranean basin countries, the dairy sheep production is usually based on local breeds, which are very well-adapted to their production systems and environments and can indeed guarantee income, employment, and economic viability in areas where production alternatives are scarce or non-existent. Mastitis is still one of the greatest problems affecting commercial milk production. However, genetic evaluation of mastitis is particularly difficult because of its low heritability and the categorical nature of the trait. The aim of this study was to identify genomic regions putatively associated with somatic cells count (SCC) in the local economically important Valle del Belice sheep breed using of deregressed breeding values (DEBV) as response variables. All the samples were genotyped using the Illumina OvineSNP50K BeadChip. Genome-wide association analysis was carried out based on regression of DEBV. A total of eight markers were found to be significantly associated with log-transformed SCC. Several candidate genes associated with SCC were identified related to immunity system and udder conformation. The results can help improving the competitiveness of the local Valle del Belìce breed. Further studies considering a higher sample size or independent population will be needed to confirm our results.

Effect of somatic cell count on milkability and milk composition of ewes

The trial aimed to study the effect of somatic cell count, breed, milk flow type, and parity on the milkability and milk composition of ewes. The flock consists of purebred Lacaune ewes (LC; n = 29) and crossbreds ewes of Improved Valachian (IV x LC; n = 35) and Tsigai (TS x LC; n = 37) with LC (with a genetic portion of Lacaune 25 and 50%). Ewes were assigned according to somatic cell count (SCC) to one of the following three groups: SCC ≤300,000 cells per mL (SCC Group 300,000), SCC between 300,000 and 1000,000 cells per mL (SCC Group 300,000 – 1000,000), SCC ≥1000,000 cells per mL (SCC Group 1000,000). 56% of evaluated ewes had less than 300,000 cells per mL and 29% more than 1000,000 cells per mL in milk. No significant differences were observed between different groups of SCC in total, machine milk yield, and the proportion of milk yield in 30 s and 60 s. The significant differences were observed between SCC Group 300,000 and SCC Group 300,000 – 1000,000 in the proportion of machine stripping from total milk yield (41 ±2 vs. 57 ±4%). Milk flow type had a significant effect on all evaluated milkability parameters but not on milk composition. Ewes on fourth parity had the highest proportion of machine stripping from total milk yield then ewes on third, fifth, and sixth and higher (60% vs. 47, 45, 46%; resp.). Effect of SCC Group on milk composition manifested only in solids not fat. The significant differences were observed between SCC Group 1000,000 to SCC Group 300,000 and SCC Group 300,000 – 1000,000 (10.75 ±0.08% vs. 11.05 ±0.06 and 11.15 ±0.11%, p ≤0.0004).

Adipose stem cells in reparative goat mastitis mammary gland

Mesenchymal stem cells have been widely used in the treatment of various chronic diseases. The objective of this survey was to evaluate the therapeutic and regenerative potential of stem cells from adipose tissue (ASCs) in the milk production recovery repair of tissue injury in mastitis goats treated with antimicrobial agents prior to cell therapy. After the diagnosis of mastitis and treatment with gentamicin, eight lactating goats were selected for cellular and subsequent therapy, physical-chemical analysis of milk, ultrasonographic and histopathological examinations. The ASCs were taken from the subcutaneous fat of a young goat cultivated in vitro, marked with Qdots-655 and injected in the left mammary gland, being the right mammary gland used as the control. After 30 days the ultrasonographic and histopathological analyzes were repeated and, in the first lactation period, the physical-chemical analysis of the milk was reapeated. Before the cellular therapy, the physical-chemical quality of the milk was compromised and the ultrasonographic and histopathological analysis revealed a chronic inflammatory process and fibrous tissue. The marking of the ASCs with Qdots enabled the tracking, by fluorescence microscopy (BX41-OLYMPUS), in the mammary tissue. In the ASCs therapy, cultures showed high cellularity and characteristics favorable to preclinical studies; with the therapy the physical-chemical parameters of the milk, fat, protein, temperature and pH showed significant differences among the groups; five animals treated with ASCs reconstituted the functionality of the gland and the connective tissue reduced in quantity and inflammatory infiltrate cells. ASCs have potential for the possible regeneration of fibrous mastitis lesions in the mammary gland, however, it would be necessary to increase injection time for the histopathological analysis, since the reconstitution of the glandular acini within the assessed period was not finalized. ASCs can be used to reestablish milk production in goat with chronic mastitis repair mammary lesions, with potential to be a promising clinical alternative for animal rehabilitation for productivity.

Role of staphylococci in mastitis in sheep

Staphylococci have been isolated from various sites of the body of healthy sheep, as well as from many infections of those animals, the main one being mastitis. The objective of this review is to appraise the importance and significance of staphylococci in causing mastitis in ewes. The review includes a brief classification and taxonomy of staphylococci and describes the procedures for their isolation and identification, as well as their virulence determinants and the mechanisms of resistance to antibacterial agents. Various staphylococcal species have been implicated in staphylococcal mastitis and the characteristics of isolates are discussed with regards to potential virulence factors. Staphylococcal mastitis is explicitly described, with reference to sources of infection, the course of the disease and the relevant control measures. Finally, the potential significance of staphylococci present in ewes' milk for public health is discussed briefly.

Udder types and associated traits affect milk composition and subclinical mastitis in Karayaka sheep

This study was carried out to determine the relationships between udder type and udder traits and milk composition and subclinical mastitis in Karayaka sheep. For this purpose, udder types were determined and udder and teat traits were measured in 32 Karayaka sheep. In addition, milk fat, protein, lactose, dry matter contents, freezing point, SCC and pH were measured. Our results showed that udder type had an effect on right (RTL) and left (LTL) teat length, right (RTDM) and left (LTDM) teat diameter and teat distance (TD). In addition, udder type was found to have an effect on lactose and pH. High or moderate phenotypic correlations were found between teat traits and lactose, freezing point and pH. In addition, of the phenotypic correlations between udder and teat traits, only the correlation between RTL and SCC was significant. SCC showed high phenotypic correlations with fat, lactose, dry matter, protein, freezing point and pH. Our results showed that udder type was effective on teat size, the sheep whose teats were vertical had low milk lactose and high pH, and the sheep with this type of udder were found to have a higher probability of mastitis.

A large-scale study of indicators of sub-clinical mastitis in dairy cattle by attribute weighting analysis of milk composition features: highlighting the predictive power of lactose and electrical conductivity

Sub-clinical mastitis (SCM) affects milk composition. In this study, we hypothesise that large-scale mining of milk composition features by pattern recognition models can identify the best predictors of SCM within the milk composition features. To this end, using data mining algorithms, we conducted a large-scale and longitudinal study to evaluate the ability of various milk production parameters as indicators of SCM. SCM is the most prevalent disease of dairy cattle, causing substantial economic loss for the dairy industry. Developing new techniques to diagnose SCM in its early stages improves herd health and is of great importance. Test-day Somatic Cell Count (SCC) is the most common indicator of SCM and the primary mastitis surveillance approach worldwide. However, test-day SCC fluctuates widely between days, causing major concerns for its reliability. Consequently, there would be great benefit to identifying additional efficient indicators from large-scale and longitudinal studies. With this intent, data was collected at every milking (twice per day) for a period of 2 months from a single farm using in-line electronic equipment (346 248 records in total). The following data were analysed: milk volume, protein concentration, lactose concentration, electrical conductivity (EC), milking time and peak flow. Three SCC cut-offs were used to estimate the prevalence of SCM: Australian ≥ 250 000 cells/ml, European ≥200 000 cells/ml and New Zealand ≥ 150 000 cells/ml. At first, 10 different Attribute Weighting Algorithms (AWM) were applied to the data. In the absence of SCC, lactose concentration featured as the most important variable, followed by EC. For the first time, using attribute weighted modelling, we showed that the concentration of lactose in milk can be used as a strong indicator of SCM. The development of machine-learning expert systems using two or more milk variables (such as lactose concentration and EC) may produce a predictive pattern for early SCM detection.

Characteristics of resistance and virulence factors in different species of coagulase-negative staphylococci isolated from milk of healthy sheep and animals with subclinical mastitis

Coagulase-negative staphylococci (CNS) are among the main responsible agents for mastitis in sheep. Cure rates can be reduced due to several causes, such as those related to virulence factors presented by microorganisms. This study aims at characterizing the virulence and resistance factors to antimicrobial agents in different CNS species isolated from sheep milk. After collecting milk samples, the samples were analyzed and the CNS species were identified. After identification, the susceptibility-sensitivity profile was examined using the disk diffusion technique for 10 antimicrobial agents. The DNA was extracted to detect the presence of the mecA gene, biofilm (icaADBC, bap, and bhp) and toxin genes (sea, seb, sec, sed, tst, and luk-PV) by PCR. Samples carrying toxin genes had their expression assessed using the reverse-transcription PCR technique. The biofilm production was assessed using the adherence method on a polystyrene plate. One hundred twelve CNS samples were isolated, 53 (47.3%) from animals with subclinical mastitis and 59 (52.7%) from healthy animals. Drugs tested have shown to be efficient for most CNS samples. The largest resistance percentage of CNS was found for the penicillin (17.0%) and tetracycline (10.7%) and 4 samples carried the mecA gene. As for the biofilm genes, the icaADBC operon was found in 10 (8.9%) samples, the bap gene was found in 16 (14.3%), and the bhp gene was found in 3 (2.7%). In addition, 69 (61.6%) samples produced biofilm. The survey of toxin genes has shown that 70 (62.5%) samples showed some toxin-encoding gene. However, none of the samples has expressed any of the genes from those toxins studied.

Relationship of mammary gland health status and other noninfectious factors with electrical conductivity of milk in Manchega ewes

Measuring the electrical conductivity (EC) of milk during milking has been extensively studied in cattle as a low-cost mastitis detection method that can be easily automated. The aim of this work was to study the effect of the health status of the glands and several noninfectious factors (lactation stage, milking session, and lactation number) that affect the use of EC measurement of milk to detect mastitis in dairy sheep livestock. Likewise, we studied the relation between EC and milk composition (macrocomposition and mineral content) and between EC and somatic cell count (SCC). Finally, we evaluated the use of EC thresholds as a mastitis detection method. To this end, we monitored the glandular milk EC throughout 2 consecutive lactations, during which 42 and 40 ewes were controlled, respectively. We carried out 7 biweekly checks, analyzing the EC, SCC, composition, and mineral content of glandular milk at morning and evening milkings. Before the morning milking, samples were aseptically collected for bacteriological analysis, and the results along with the SCC were used to classify the glands according to their sanitary status (healthy, latently infected, or infected). Lactation stage, parity, milking (morning or evening), health status, and the interactions of parity with health status, lactation stage with health status, and parity with lactation stage all had a significant effect on SCC and EC of the milk. The correlation between EC and SCC was only significant when all the data were analyzed jointly (r = 0.33) and for SCC ≥ 600.000 cells/mL (r = 0.25). The changes in milk composition, mainly in fat content, largely explained the variation in EC (R² = 0.69). For the same EC threshold, the specificity and sensitivity varied depending on the parity or the milking, with the negative predictive value obtained being higher than the positive predictive value at all times. We concluded that developing methods of detecting mastitis in sheep by milk EC readings would require consideration of noninfectious factors that also affect the gauging of EC. One option to consider would be individualized daily monitoring of the glands, as demonstrated in other species such as cattle and goat.

COMPOSIÇÃO DO LEITE DE CABRAS SAANEN INFECTADAS EXPERIMENTALMENTE COM Staphylococcus aureus E SUBMETIDAS A DOIS PROTOCOLOS DE TRATAMENTO

Resumo: Neste estudo, objetivou-se avaliar a composição química do leite após a infecção e tratamento da mastite induzida por S. Aureus. Foram utilizadas 10 fêmeas caprinas da raça Saanen. Fez-se a infecção experimental em 20 glândulas mamárias, formando-se quatro grupos experimentais, sendo cada um composto por cinco glândulas mamárias. Um grupo foi tratado com antimicrobiano comercial e outro com pomada à base de extrato natural de planta. Os demais grupos foram constituídos controles. Os valores obtidos para gordura, lactose, proteína, sólidos totais e produção leiteira foram analisados ao longo dos momentos experimentais, comparando-os entre si e entre os grupos experimentais. A mastite foi diagnosticada 24 horas pós inoculação, utilizando-se a lactocultura. Os animais não apresentaram alterações nos parâmetros clínicos avaliados. Para os percentuais de gordura, proteína e sólidos totais, observou-se uma elevação ao longo dos momentos experimentais, sem variação entre os grupos experimentais. Tendo em vista a importância da terapia antimicrobiana convencional e a crescente utilização de antimicrobianos naturais, os resultados obtidos mostram igualdade entre as duas opções terapêuticas, principalmente no aspecto de manutenção dos principais componentes do leite.

Assessment of genetic variation for pathogen-specific mastitis resistance in Valle del Belice dairy sheep

Background

Mastitis resistance is a complex and multifactorial trait, and its expression depends on both genetic and environmental factors, including infection pressure. The objective of this research was to determine the genetic basis of mastitis resistance to specific pathogens using a repeatability threshold probit animal model.

Results

The most prevalent isolated pathogens were coagulase-negative staphylococci (CNS); 39 % of records and 77 % of the animals infected at least one time in the whole period of study. There was significant genetic variation only for Streptococci (STR). In addition, there was a positive genetic correlation between STR and all pathogens together (ALL) (0.36 ± 0.22), and CNS and ALL (0.92 ± 0.04).

Conclusion

The results of our study support the presence of significant genetic variation for mastitis caused by Streptococci and suggest the importance of discriminating between different pathogens causing mastitis due to the fact that they most likely influence different genetic traits. Low heritabilities for pathogen specific-mastitis resistance may be considered when including bacteriological status as a measure of mastitis presence to implement breeding strategies for improving udder health in dairy ewes.

Composition, proteolysis indices and coagulating properties of ewe milk as affected by bulk tank somatic cell count

The aim of this study was to assess the effect of ovine bulk tank somatic cell count (BTSCC) on composition, proteose-peptone (p-p) content and casein fractions as indicating parameters for proteolysis and coagulating properties of milk. A total of 97 samples of bulk tank milk from Manchega breed ewe flocks were grouped according to somatic cell count (SCC) into four classes: fewer than 500,000 cells/ml, from 500,000 to 10,00000 cells/ml, from 10,00000 to 15,00000 and more than 15,00000 cells/ml. The casein : protein ratio and lactose content decreased with BTSCC. Proteolysis increased with BTSCC, causing a drop in β-casein and an increase in the γ-caseins from a concentration of 500,000 cells/ml. Regarding coagulation behaviour, the rennet clotting time (RCT) and firming time (k20) rose from 10,00000-15,00000 cells/ml of milk. The results showed that the impairment of milk quality and milk ability to make cheese as affected by intramammary infection (IMI) can be inferred from the bulk tank milk of flocks with poor udder health.

Use of milk amyloid A in the diagnosis of subclinical mastitis in dairy ewes

Subclinical mastitis (SM) is one of the most important diseases affecting dairy ewes worldwide, with negative impact on the animal health, farm income and public health. Animals with SM often remain untreated because the disease may not be revealed. Increase in somatic cell count (SCC) and positive bacteriology for mastitis pathogens in milk samples are indicative of SM but the evidence of only one of these alterations must suggest an uncertain SM (UM). UM is defined when positive bacteriological examination (Latent-SM) or SCC>500 000 cells/ml (non-specific-SM) are detected in milk. Nevertheless, SCC and bacteriological examination are expensive, time consuming and are not yet in use at the farm level in dairy ewes. Recently, a sensitive acute phase protein, amyloid A, displaying multiple isoforms in plasma and different body fluids including mammary secretion (milk amyloid A-MAA), has been investigated as a marker of mastitis in cows and, in a few studies, in sheep. The aim of this trial was to compare the concentration of MAA of single udder-halves in ewes with healthy udder-halves (HU-control group) and naturally occurring subclinical mastitis, both confirmed (SM group) and uncertain (UM groups: Latent-SM and non-specific-SM), for monitoring udder health. The reliability of a specific ELISA kit for the measurement of MAA was also tested. During a 3-month trial period, 153 udder halves were assigned to the experimental groups based on their health status: 25 with SM, 40 with UM (11 with latent-SM and 29 with non-specific-SM) and 88 HU. SCC and bacteriological analysis were performed to establish the control and subclinical mastitis groups. MAA concentrations in milk samples were measured using a specific commercially milk ELISA kit. The data were submitted to statistical analysis. Significant (P<0·05) differences among the groups SM, non-specific-SM and HU were detected with the SM having the highest level and HU the lowest. MAA concentration is affected by the udder health status and is a useful indicator of subclinical mastitis and increased SCC in sheep.

Estafilococos resistentes à oxacilina isolados em casos de mastite subclínica em ovinos

Bactérias do gênero Staphylococcus estão entre os principais agentes causadores da mastite ovina. Um dos maiores entraves ao tratamento dos animais doentes são cepas resistentes aos antimicrobianos empregados. A pesquisa do gene mecA nos estafilococos é um instrumento auxiliar para a determinação de aspectos epidemiológicos da doença. Este trabalho teve por objetivo investigar a resistência à oxacilina em estafilococos coagulase-negativos isolados no leite de ovelhas com mastite subclínica. Foram analisadas 448 amostras de leite de dois rebanhos. Os micro-organismos isolados foram submetidos previamente a testes de sensibilidade a antibióticos in vitro a partir da técnica de difusão em disco. Naqueles resistentes à oxacilina nestes testes efetuou-se a pesquisa do gene mecA, com a extração do DNA cromossômico por meio da técnica de extração fenol-clorofórmio. Os estafilococos coagulase-negativos apresentaram resistência à oxacilina e a presença do gene mecA foi detectada em quatro isolados, que também apresentaram características de multirresistência. Tais achados reforçam a importância deste grupo de micro-organismos na etiologia da mastite subclínica em ovinos e abre perspectivas para futuras pesquisas para a investigação da epidemiologia da doença.

Effects of somatic cells on the protein profile of hard ovine cheese produced from different breeds

Bulk tank ewe's milks with low (<500,000 ml−1), medium (1,000,000–1,500,000 ml−1) and high (>2,500,000 ml−1) somatic cell counts (SCC) from three breeds were used to manufacture hard ewes’-milk cheese. Physico-chemical analysis and capillary electrophoresis of fresh cheeses and cheeses that had been ripened for 1, 2, 3 and 6 months were carried out. The results showed that high SCC levels in milk affected the moisture content of only freshly made cheeses and the pH, fat content and fat acidity of ripened cheeses. Regarding proteolysis, the levels of all β-CNs in freshly made cheeses were significantly lower as the SCC values increased and the Castellana breed was the most affected by SCC levels because a significant decrease in all α-CNs was also observed as SCC levels rose. Analysis of the casein profile by principal component analysis (PCA) revealed that there were no clear differences according the SCC up to the third month. However in the third and sixth months cheeses with low levels of SC were closely grouped and characterised by the highest levels of intact caseins. Regarding the effect of breed, the results point to a more intense proteolytic activity in the Assaf breed, whose more matured cheeses showed the highest content of casein proteolytic fragments.

Genetic parameters for somatic cell score according to udder infection status in Valle del Belice dairy sheep and impact of imperfect diagnosis of infection

Background

Somatic cell score (SCS) has been promoted as a selection criterion to improve mastitis resistance. However, SCS from healthy and infected animals may be considered as separate traits. Moreover, imperfect sensitivity and specificity could influence animals' classification and impact on estimated variance components. This study was aimed at: (1) estimating the heritability of bacteria negative SCS, bacteria positive SCS, and infection status, (2) estimating phenotypic and genetic correlations between bacteria negative and bacteria positive SCS, and the genetic correlation between bacteria negative SCS and infection status, and (3) evaluating the impact of imperfect diagnosis of infection on variance component estimates.

Methods

Data on SCS and udder infection status for 1,120 ewes were collected from four Valle del Belice flocks. The pedigree file included 1,603 animals. The SCS dataset was split according to whether animals were infected or not at the time of sampling. A repeatability test-day animal model was used to estimate genetic parameters for SCS traits and the heritability of infection status. The genetic correlation between bacteria negative SCS and infection status was estimated using an MCMC threshold model, implemented by Gibbs Sampling.

Results

The heritability was 0.10 for bacteria negative SCS, 0.03 for bacteria positive SCS, and 0.09 for infection status, on the liability scale. The genetic correlation between bacteria negative and bacteria positive SCS was 0.62, suggesting that they may be genetically different traits. The genetic correlation between bacteria negative SCS and infection status was 0.51. We demonstrate that imperfect diagnosis of infection leads to underestimation of differences between bacteria negative and bacteria positive SCS, and we derive formulae to predict impacts on estimated genetic parameters.

Conclusions

The results suggest that bacteria negative and bacteria positive SCS are genetically different traits. A positive genetic correlation between bacteria negative SCS and liability to infection was found, suggesting that the approach of selecting animals for decreased SCS should help to reduce mastitis prevalence. However, the results show that imperfect diagnosis of infection has an impact on estimated genetic parameters, which may reduce the efficiency of selection strategies aiming at distinguishing between bacteria negative and bacteria positive SCS.

Effect of somatic cell counts on ewes' milk protein profile and cheese-making properties in different sheep breeds reared in Spain

Bulk tank ewe's milks from Assaf, Castellana and Churra breeds categorized within three different Somatic Cell Count (SCC) groups (LSCC: <500 000; MSCC: 1 000 000 to 1 500 000; and HSCC: 2 500 000 to 3 000 000 cells ml−1) were used to investigate changes in capillary electrophoresis protein profiles and cheese-making properties. The results do not reveal a significant effect of SCC on total casein contents, because the sum of β-caseins decreased as SCC increased; no statistically significant differences were observed for the sum of α-caseins, and the values of κ-casein were higher in the HSCC milk. However, the soluble proteins other than α-lactalbumin and β-lactoglobulin increased with SCC. Regarding the effect of breed, the Assaf breed had the lowest contents of κ-CN, αs1-I-CN, αs1-II-CN 1-CN, αs1-III-CN, β1-CN and β2-CN. The protein profile was significantly correlated with curd textural properties. αs1-I-CN was the most influential variant because it was positively correlated with a large number of textural parameters. Cheese yield was positively correlated with all casein variants except αs1-III-CN, showing that the milk from local breeds were more suitable for cheese-making due to their higher contents of all the casein variants. Regarding curd texture properties LSCC milk curds showed more cohesiveness, associated with its lower content of αs1-III-CN and Castellana milk curds showed the highest values for firmness owing to their higher content of αs1-I-CN.

Effects of experimental challenge of ewes with Mannheimia haemolytica on subsequent milk composition

The objective was to describe the physicochemical changes during the early phase of subclinical mastitis and to associate them with pathological findings. A Mannheimia haemolytica strain was deposited into one teat duct of 25 ewes and the clinical, bacteriological, cytological, physicochemical (pH, milk composition), gross-pathological and histological findings were subsequently recorded. The organism was consistently isolated from samples of teat duct material (140/150) but not from mammary secretion (50/150). California Mastitis Test (CMT) scores increased (>1) and remained high (143/150 samples) after challenge; polymorphonuclear neutrophils (PMN) predominated in milk films, but the proportion of lymphocytes and macrophages progressively increased. Increased pH values (>7.0) were recorded in the mammary secretion from the challenged side. Furthermore, content of fat, total proteins and lactose therein decreased markedly. Histological changes (leucocytic infiltration, destruction of epithelial cells) were observed in the mammary parenchyma of the ewes. The present results confirm that the reduction of milk constituents is the effect of cellular damage and can occur soon after infection.

Outbreak of subclinical mastitis in a flock of dairy goats associated with atypicalStaphylococcus haemolyticus

Staphylococcus haemolyticusis a pathogen frequently isolated from dairy cows and small ruminants. However, it always appears in only a few animals and not as a major pathogen. Recently, in a dairy goat herd of approximately 250 milking animals, 25·6% (46/180 goats) had milk cultures with atypical highly mucoid colonies accompanied by elevated somatic cell counts. The isolates were identified asStaph. haemolyticus. The present study describes the steps used in an attempt to identify the bacterium and to compare it with other coagulase-negative staphylococci (CNS) includingStaph. haemolyticus. Species identification performed with the API STAPH-IDENT 32 kit showed >99·4% identity confirmed by 16S rDNA sequencing tests. Microscopically the atypicalStaph. haemolyticusstrains showed unique cuboidal tetrad clusters reminiscent of those of the genusSarcina. The outbreak caused by an atypical CNS underlines the need for accurate biochemical and genetic methods for ultimate identification of CNS to the species level.

Influence of Somatic Cell Count and Breed on Capillary Electrophoretic Protein Profiles of Ewes’ Milk: A Chemometric Study

Bulk tank ewe milk from the Assaf, Castellana, and Churra breeds categorized into 3 somatic cell count (SCC) groups (<500,000; 1,000,000 to 1,500,000; and >2,500,000 cells/mL) was used to investigate changes in chemical composition and capillary electrophoresis protein profiles. The results obtained indicated that breed affected fat, protein, and total solids levels, and differences were also observed for the following milk proteins: beta-, beta1-, beta2-, and alpha(s1)-III-casein, alpha-lactalbumin, and beta-lactoglobulin. High SCC affected fat and protein contents and bacterial counts. The level of beta1-, beta2-, and alpha(s1)-I-casein, and alpha-lactalbumin were significantly lower in milk with SCC scores >2,500,000 cells/mL. A preliminary study of the chemical, microbiological, and electrophoretic data was performed by cluster analysis and principal components analysis. Applying discriminant analysis, it was possible to group the milk samples according to breed and level of SCC, obtaining a prediction of 100 and 97% of the samples, respectively.

Aspectos clínicos e características do leite em ovelhas com mastite induzida experimentalmente com Staphylococcus aureus

Este trabalho teve por objetivo estudar os aspectos clínicos e as características físico-químicas do leite em ovelhas com mastite induzida experimentalmente com Staphylococcus aureus. Foram utilizados dez animais da raça Santa Inês, com peso médio de 30 kg, fêmeas, primíparas recém-paridas, mantidos em apriscos e clinicamente sadios. Após se estabelecer os padrões de normalidade para as variáveis estudadas, os animais foram inoculados experimentalmente numa mama com uma cepa de S. aureus, empregando-se o inóculo de 1,0x10(4)ufc/ml, enquanto a outra serviu como controle. As observações clínicas e laboratoriais foram realizadas nos intervalos de 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, 132, 168, 180, 288 e 336 horas após a inoculação do agente etiológico (PI). Todos os animais apresentaram manifestações clínicas sistêmicas e nas glândulas inoculadas, observadas com mais intensidade a partir de 24 horas após a inoculação. Alterações significativas (P<0,05) na produção e nos componentes físico-químicos do leite em relação aos seus controles ocorreram, reduzindo o volume e gordura. O pH, o teor de cloretos e a CCS atingiram índices muito elevados (P<0,05), acompanhados da reação na prova do CMT. O exame bacteriológico revelou a presença do S. aureus durante a fase de infecção. Após a instituição do tratamento nas ovelhas às 36 h PI, um animal morreu 48h PI; nas demais ocorreu a recuperação clínica, no entanto não houve o restabelecimento fisiológico das mamas inoculadas, que perderam a sua funcionalidade.

Changes in milk composition as affected by subclinical mastitis in goats

The mechanism of the effects of subclinical mastitis (SM) at the glandular level in dairy goats on milk yield and its composition as expressed in curd yield (Yc) was studied. Twenty-five Israeli goats of various crossbreeds were chosen; one udder half was naturally infected with identified coagulase-negative staphylococci, and the contralateral gland was free of bacteria. The milk yield of the infected halves was significantly lower than that of the uninfected ones. Somatic cell count and N-acetyl-beta-D-glucosaminidase activity were significantly higher in the infected halves. The lactose concentration in the infected glands was significantly lower than that in the uninfected ones, casein concentrations did not differ, and the whey protein and albumin concentrations were significantly higher in the infected glands. Plasmin activity was significantly higher in the infected glands, whereas plasminogen activity was undetectable. Concentrations of Ca2+ did not differ, whereas Ca2+ activity was significantly lower in the infected glands. The proteose peptone concentration was 1.5 times as great in the infected glands as in the uninfected ones. The Yc was significantly lower in the infected halves, and clotting time was significantly longer. The mechanisms of the effects of SM on milk yield and Yc in goats and sheep are discussed and compared.