Use of somatic cell counts for the detection of subclinical mastitis in sheep

Polymorphism of Selected Regions of Ovar-MHC and the Health Status of the Ovine Mammary Gland

Udder diseases (mastitis) are a serious cause of economic losses in sheep breeding as they have a negative impact on lamb rearing and the quality of dairy products. Thus far, progress in treatment and prevention of these diseases has been insufficient-giving ground for searching possibilities of using natural immunity to combat mastitis. This study aims to assess the relationship between the microsatellite polymorphism of selected Ovar-MHC genes and the health status of the mammary gland of sheep. The research is carried out on sheep of the Polish Heath and Polish Lowland breeds. In ovine milk, the SCC and the percentage of the lymphocyte subpopulation are assessed. Based on genomic DNA, molecular analysis of the Ovar-MHC gene fragments (OLADRB1, OLADRB2, OMHC1) polymorphism is performed. Significant differences are found in SCC level and the percentage of lymphocytes (CD4, CD8, CD19) in the milk depending on the alleles of the Ovar-MHC genes. Alleles of 488 bp (DRB1) and 284 bp (DRB2) are found more frequently in sheep, which milk contained <200 × 10³/mL SCC, while in carriers of the 508 bp (DRB1) and 272 bp (DRB2) alleles, SCC level in milk is significantly higher (>200 × 10³/mL). The obtained results justify the need for further research to better understand the genetic basis of mastitis, and to search for effective molecular markers that can be used in breeding practice.

Novel Biomarkers of Mastitis in Goat Milk Revealed by MALDI-TOF-MS-Based Peptide Profiling

Mastitis is the most common infection of dairy goats impairing milk production and quality, which is usually recognized by mammary gland visual inspection and palpation. Subclinical forms of the disease are also widely represented, which lack the typical signs of the clinical ones but are still associated with reduced production and safety for human consumption of milk, generally presenting a high bacterial count. In order to obtain novel analytical tools for rapid and non-invasive diagnosis of mastitis in goats, we analyzed milk samples from healthy, subclinical and clinical mastitic animals with a MALDI-TOF-MS-based peptidomic platform, generating disease group-specific spectral profiles whose signal intensity and mass values were analyzed by statistics. Peculiar spectral signatures of mastitis with respect to the control were identified, while no significant spectral differences were observed between clinical and subclinical milk samples. Discriminant signals were assigned to specific peptides through nanoLC-ESI-Q-Orbitrap-MS/MS experiments. Some of these molecules were predicted to have an antimicrobial activity based on their strong similarity with homolog bioactive compounds from other mammals. Through the definition of a panel of peptide biomarkers, this study provides a very rapid and low-cost method to routinely detect mastitic milk samples even though no evident clinical signs in the mammary gland are observed.

Bacteriological cure rate and changes in milk composition in mastitis vaccinated ewes affected with subclinical mastitis

Aim:

The aim of this study was to investigate the effects of using a commercially-available polyvalent mastitis vaccine on the bacteriological cure rate of existing subclinical mastitis in Awassi sheep.

Materials and Methods:

A total of 164 lactating ewes were divided into two main groups according to udder health and milk somatic cell count (SCC): Group 1=normal (N; n=80) and Group 2=subclinical mastitis (SC; n=84). Each group was then subdivided randomly into two treatment groups: N vaccinated (N_vax; n=38), N non-vaccinated (N_nvax; n=42), SC vaccinated (SC_vax; n=42), and SC non-vaccinated (SC_nvax; n=42). The vaccine was administered as per manufacturer’s recommendations. Milk samples were collected aseptically from all ewes before vaccine administration (T0) and again on days 28 (T2) and 42 (T3) of the experiment.

Results:

In the SC group, the bacteriological cure rates in vaccinated and non-vaccinated ewes were 76% and 69%, respectively. In N group, the new intramammary infection rates in vaccinated and non-vaccinated ewes were 48% and 50%, respectively. Vaccination of normal ewes resulted in a significant (p<0.05) reduction in bacterial growth rate both at day 28 and day 42 of the study. The prevalence of new intramammary infection rate in N_vax ewes on days 28 and 42 was 19% and 20%, respectively. The prevalence of new intramammary infection rate in N_nvax group on days 28 and 42 was 33% and 30%, respectively. In SC_vax group, the bacterial growth rate on days 28 and 42 was 44% and 35%, respectively. In SC_nvax group, the bacterial growth rate on days 28 and 42 was 27% and 32%, respectively. There was no statistically significant effect of vaccination on any of the studied milk composition parameters.

Conclusions:

This is a preliminary study that indicated a possible protective effect of vaccination against mastitis in sheep. Further, case-controlled studies are indicated to estimate the level of immunity this vaccine provides to vaccinated sheep.

Defining the breeding goal for a sheep breed including production and functional traits using market data

In this study, the economic values for production and functional traits of dairy sheep are estimated through the application of a profit function model using farm-level technical and economic data. The traits incorporated in the model were milk production, prolificacy, fertility, milking speed, longevity and mastitis occurrence. The economic values for these traits were derived as the approximate partial derivative of the specified profit function. A sensitivity analysis was also conducted in order to examine how potential changes in input and output prices would affect the breeding goal. The estimated economic values of the traits revealed their economic impact on the definition of the breeding goal for the specified production system. Milk production and fertility had the highest economic values (€40.30 and €20.28 per standard genetic deviation (SDa)), while, mastitis only had a low negative value of -0.57 €/SDa. Therefore, breeding for clinical mastitis will have a minor impact on farm profitability because it affects a small proportion of the flock and has low additive variance. The production traits, which include milk production, prolificacy and milking speed, contributed most to the breeding goal (70.0%), but functional traits still had a considerable share (30.0%). The results of this study highlight the importance of the knowledge of economic values of traits in the design of a breeding program. It is also suggested that the production and functional traits under consideration can be categorized as those which can be efficiently treated through genetic improvement (e.g. milk production and fertility) while others would be better dealt with through managerial interventions (e.g. mastitis occurrence). Also, sub-clinical mastitis that affects a higher proportion of flocks could have a higher contribution to breeding goals.

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.

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.

MONITORAMENTO MICROBIOLÓGICO DA MASTITE OVINA NA REGIÃO DE BAURU, SP

RESUMO As mastites são inflamações agudas ou crônicas da glândula mamária, caracterizadas por alte-rações físicas, químicas e bacteriológicas no leite. O leite ovino tem ocupado uma importância cada vez maior no mercado, podendo ser utilizado na produção de queijo e outros derivados, contribuindo para o aumento da receita do produtor rural. Entretanto, a mastite pode determinar redução, tanto na quantidade quanto na qualidade do leite produzido, levando à redução do ganho de peso dos cordeiros e causando aumento da mortalidade nos animais. Ressalta-se ainda o aspecto de saúde pública, pela redução do nível de nutrientes, assim como a intensa multiplicação microbiana que pode ocasionar diarreias e outras zoonoses. Pretendeu-se com este trabalho avaliar a frequência de casos de mastite em 159 ovelhas procedentes de vinte pequenas propriedades localizadas em Bauru, SP, e região. Das 309 amostras colhidas, em 97 (31,4%) foram isolados micro-organismos do gênero Staphylococcus sp., sendo 27,5% Staphylococcus sp. coagulase negativos e 3,9% Staphylococcus sp. coagulase positivos. Dos 177 isolamentos, 97 (54,8%) foram representados pelo gênero Staphylococcus, sendo 57 (58,8%) obtidos em cultura pura e 40 (41,2%) em associação. A maioria dos agentes isolados foi sensível aos antimicrobianos utilizados no teste. Assim, pôde-se verificar o isolamento de micro-organismos contagiosos, como Staphylococcus sp. coagulase negativo e positivo, sendo que, assim como na bovinocultura leiteira, medidas de profilaxia para obtenção higiênica do leite são de extrema importância para adquirir-se um produto final de qualidade, e seguro do ponto de vista microbiológico e alimentar.

The potential of measuring serum amyloid A in individual ewe milk and in farm bulk milk for monitoring udder health on sheep dairy farms

The aim of the study was to determine the diagnostic value of measuring serum amyloid A (SAA) concentrations in milk of individual ewes and in farm bulk milk for monitoring udder health. Udder health was calculated by examining a randomly selected group of seven flocks at each farm visit by means of California mastitis test and bacteriological examination of 5749 milk samples. SAA was determined additionally in 267 randomly selected milk samples from six flocks. Thirty-one bulk milk samples from these farms were tested for SCC and SAA levels. Subclinical infections were detected in 29.5% of samples whereas no clinical infections were observed. Intramammary infected udder halves showed significantly elevated SAA concentrations (121.3+/-25.3 microg/ml) in milk compared to the levels of healthy udder halves (8.0+/-1.9 microg/ml; p<0.001). SAA was significantly elevated in sheep with elevated CMT scores and positive bacteriological results. Bulk milk SAA levels ranged from 18.6+/-6.7 to 37.4+/-14.1 microg/ml and showed a positive correlation with bSCC (r=0.38, p=0.018) but not with percent infected glands (r=0.022, p=0.453). This study demonstrated that SAA levels in milk can be used to detect subclinical mastitis in individual ewes whereas further investigations are needed to determine the value of measuring SAA in bulk milk for monitoring flock udder health.

Genotyping of Staphylococcus aureus isolated from various sites on farms with dairy sheep using pulsed-field gel electrophoresis

We investigated the genetic diversity of 179 Staphylococcus aureus isolates recovered from various sites in 10 farms producing cheeses manufactured with raw ewe's milk. Isolates were collected from handcrafted cheeses, bulk tank milk, milk from half-udders, skin abscesses on the udder if present, hands and anterior nares of farmers, and air of the milking area. The isolates were typed using pulsed-field gel electrophoresis (PFGE) of DNA SmaI digests and compared to other isolates of S. aureus isolated in different hosts or in different locations. The results showed that nine farms were contaminated by S. aureus isolates with identical banding patterns (named OV) or by genetically related isolates (named OV'). These dominant banding patterns were found in a variable proportion of the samples from each farm (range: 11-100%). Most of the strains isolated from nasal carriage or strains isolated from other regions or from other animal species had different PFGE patterns to OV or OV', except for three strains. These results show that a single clone of S. aureus is widely distributed both in infected mammary glands and in cheese produced from raw milk. This study confirms that infected mammary glands are the main source of the contamination of dairy products in sheep.

Serum amyloid A in the serum and milk of ewes with mastitis induced experimentally with Staphylococcus epidermidis

Mastitis was induced experimentally in ewes with Staphylococcus epidermidis, and the concentrations of serum amyloid A (SAA) in milk and serum, and the somatic cell counts and bacteria in the milk were determined for up to 10 weeks in two experiments, each examining five infected and five control ewes. The somatic cell counts peaked eight hours after infection and preceded an increase in SAA in milk. A maximum concentration of 6460 microg/ml SAA was recorded in milk from the infected sheep, compared with a mean concentration of 1.4 microg/ml in the control sheep. The mean peak concentration of SAA in serum (206.8 microg/ml) occurred earlier (one day after infection) than in milk. The serum concentration of SAA in the healthy animals ranged from 0 to 29.4 microg/ml. There was no correlation between the concentrations of SAA in serum and milk.

Genetic parameters for milk somatic cell scores and relationships with production traits in French Lacaune dairy sheep

Records from 94,445 and 45,499 French Lacaune dairy ewes in first and second lactations, respectively, were used to estimate genetic parameters for somatic cell scores. Somatic cell count data came from an extensive recording scheme and sample testing that began in 1999 using the flocks enrolled in the official milk recording system. Somatic cell count data were from 2 to 4 test days per lactation. Lactation average and single test-day somatic cell scores were considered in multitrait sire models. The heritability estimate of lactation somatic cell score was close to 0.13 and similar for first and second parity. Heritabilities of somatic cell scores increased from first to fourth test day (from 0.07 to 0.11 in first lactation and from 0.05 to 0.13 in second lactation). Genetic correlations between somatic cell scores were high, usually more than 0.91, but lower between first test day and later test days in first lactation (0.64 to 0.88). The genetic correlations between lactation somatic cell score and milk yield, between lactation somatic cell score and fat content, and between lactation somatic cell score and protein content were 0.18, 0.04, and 0.03 in first lactation, respectively. The genetic antagonism between test day somatic cell score and milk yield measured in first lactation increased from beginning to the end of the lactation (0.05 to 0.23). This antagonism was slightly lower for somatic cell score in second lactation (from 0.09 to 0.14, and 0.08 for lactation mean). Environmental correlations in first lactation between lactation somatic cell score and milk yield, between lactation somatic cell score and fat content, and between lactation somatic cell score and protein content were -0.18, 0.13, and 0.30, respectively.

Relationships among somatic cell count, California mastitis test, impedance and bacteriological status of milk in goats and sheep in early lactation

The objectives of this trial were to evaluate and compare the test characteristics of a number of indirect tests of bacteriological status of the milk from goats and sheep and to assess the affect of varying levels of prevalence of infection on the performance of those tests.The somatic cell count, California mastitis test (CMT) score, electrical impedance and the bacteriological status of 220 and 262 milk samples from the glands of lactating dairy goats and sheep, respectively, were determined. The sensitivity and specificity of indirect tests in predicting the bacteriological status were compared by analyzing the areas under the receiver operating characteristic curve and calculating the likelihood ratio at various cut-off values.Bacteria were isolated from 17.7 and 4.6% of glands from goats and sheep, respectively. Somatic cell count was a better predictor of bacteriological status than either the CMT score or impedance in both goats and sheep. However, knowledge of the CMT score in both sheep and goats and the impedance in goats increases the likelihood of predicting the presence of a bacterial pathogen compared to no testing at all (P<0.05). Knowledge of the age and days postpartum of the animals at the time of testing did not increase the probability that infection status could be predicted. Variation in cut-off levels to predict infection status reported in the literature may be due to variation in the prevalence of infection in the populations studied. Use of likelihood ratio allows comparison of tests over a range of prevalence's as likelihood ratios are independent of prevalence. The prevalence of infection within a herd should be considered when selecting a cut-off value for indirect testing for the presence of bacteria in milk of small ruminants.