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The objective of this research was to estimate the genetic correlations between milk mid-infrared-predicted fatty acid groups and production traits in first-parity Canadian Holsteins. Contents of short-chain, medium-chain, long-chain, saturated, and unsaturated fatty acid groupings in milk samples can be predicted using mid-infrared spectral data for cows enrolled in milk recording programs. Predicted fatty acid group contents were obtained for 49,127 test-day milk samples from 10,029 first-parity Holstein cows in 810 herds. Milk yield, fat and protein yield, fat and protein percentage, fat-to-protein ratio, and somatic cell score were also available for these test days. Genetic parameters were estimated for the fatty acid groups and production traits using multiple-trait random regression test day models by Bayesian methods via Gibbs sampling. Three separate 8- or 9-trait analyses were performed, including the 5 fatty acid groups with different combinations of the production traits. Posterior standard deviations ranged from <0.001 to 0.01. Average daily genetic correlations were negative and similar to each other for the fatty acid groups with milk yield (-0.62 to -0.59) and with protein yield (-0.32 to -0.25). Weak and positive average daily genetic correlations were found between somatic cell score and the fatty acid groups (from 0.25 to 0.36). Stronger genetic correlations with fat yield, fat and protein percentage, and fat-to-protein ratio were found with medium-chain and saturated fatty acid groups compared with those with long-chain and unsaturated fatty acid groups. Genetic correlations were very strong between the fatty acid groups and fat percentage, ranging between 0.88 for unsaturated and 0.99 for saturated fatty acids. Daily genetic correlations from 5 to 305 d in milk with milk, protein yield and percentage, and somatic cell score traits showed similar patterns for all fatty acid groups. The daily genetic correlations with fat yield at the beginning of lactation were decreasing for long-chain and unsaturated fatty acid groups and increasing for short-chain fatty acids. Genetic correlations between fat percentage and fatty acids were increasing at the beginning of lactation for short- and medium-chain and saturated fatty acids, but slightly decreasing for long-chain and unsaturated fatty acid groups. These results can be used in defining fatty acid traits and breeding objectives., (Copyright © 2018 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The fatty acid profile of milk is a prevailing issue due to the potential negative or positive effects of different fatty acids to human health and nutrition. Mid-infrared spectroscopy can be used to obtain predictions of otherwise costly fatty acid phenotypes in a widespread and rapid manner. The objective of this study was to evaluate the prediction of fatty acid content for the Canadian dairy cattle population from mid-infrared spectral data and to compare the results produced by altering the partial least squares (PLS) model development set used. The PLS model development sets used to develop the predictions were reference fatty acids expressed as (1) grams per 100 g of fatty acid, (2) grams per 100 g of milk, (3) the natural logarithmic transform of grams per 100 g of milk, and (4) subsets of samples randomly selected by removing excess records around the mean to present a more uniform distribution, repeated 10 times. Gas chromatography measured fatty acid concentration and spectral data for 2,023 milk samples of 373 cows from 4 breeds and 44 herds were used in the model development. The coefficient of determination of cross-validation (R cv ) increased when fatty acids were expressed on a per 100 g of milk basis compared with on a per 100 g of fat basis for all examined fatty acids. The logarithmic transformation used to create a more Gaussian distribution in the development set had little effect on the prediction accuracy. The individual fatty acids C12:0, C14:0, C16:0, C18:0, C18:1n-9 cis, and saturated, monounsaturated, unsaturated, short-chain, medium-chain, and long-chain fatty acid groups had (R 2 ) increased when fatty acids were expressed on a per 100 g of milk basis compared with on a per 100 g of fat basis for all examined fatty acids. The logarithmic transformation used to create a more Gaussian distribution in the development set had little effect on the prediction accuracy. The individual fatty acids C12:0, C14:0, C16:0, C18:0, C18:1n-9 cis, and saturated, monounsaturated, unsaturated, short-chain, medium-chain, and long-chain fatty acid groups had (R cv 2 ) between the top- and bottom-performing prediction equation across the different subsets for a single predicted fatty acid was on average 0.055 depending on which samples were randomly selected to be used in the PLS model development set. Predictions for fatty acids with high accuracies can be used to monitor fatty acid contents for cows in milk recording programs and possibly for genetic evaluation.cv 2 ) values were observed for the majority of fatty acids. The difference in (R cv 2 ) between the top- and bottom-performing prediction equation across the different subsets for a single predicted fatty acid was on average 0.055 depending on which samples were randomly selected to be used in the PLS model development set. Predictions for fatty acids with high accuracies can be used to monitor fatty acid contents for cows in milk recording programs and possibly for genetic evaluation., (Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The objective of this study was to estimate the heritability of milk fat globule (MFG) size and mid-infrared (MIR) predicted MFG size in Holstein cattle. The genetic correlations between measured and predicted MFG size with milk fat and protein percentage were also investigated. Average MFG size was measured in 1,583 milk samples taken from 254 Holstein cows from 29 herds across Canada. Size was expressed as volume moment mean (D[4,3]) and surface moment mean (D[3,2]). Analyzed milk samples also had average MFG size predicted from their MIR spectral records. Fat and protein percentages were obtained for all test-day milk samples in the cow's lactation. Univariate and bivariate repeatability animal models were used to estimate heritability and genetic correlations. Moderate heritabilities of 0.364 and 0.466 were found for D[4,3] and D[3,2], respectively, and a strong genetic correlation was found between the 2 traits (0.98). The heritabilities for the MIR-predicted MFG size were lower than those estimated for the measured MFG size at 0.300 for predicted D[4,3] and 0.239 for predicted D[3,2]. The genetic correlation between measured and predicted D[4,3] was 0.685; the correlation was slightly higher between measured and predicted D[3,2] at 0.764, likely due to the better prediction accuracy of D[3,2]. Milk fat percentage had moderate genetic correlations with both D[4,3] and D[3,2] (0.538 and 0.681, respectively). The genetic correlation between predicted MFG size and fat percentage was much stronger (greater than 0.97 for both predicted D[4,3] and D[3,2]). The stronger correlation suggests a limitation for the use of the predicted values of MFG size as indicator traits for true average MFG size in milk in selection programs. Larger samples sizes are required to provide better evidence of the estimated genetic parameters. A genetic component appears to exist for the average MFG size in bovine milk, and the variation could be exploited in selection programs., (Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The objectives of this study were to investigate the sources of variation in milk fat globule (MFG) size in bovine milk and its prediction using mid-infrared (MIR) spectroscopy. Mean MFG size was measured in 2,076 milk samples from 399 Ayrshire, Brown Swiss, Holstein, and Jersey cows, and expressed as volume moment mean (D[4,3]) and surface moment mean (D[3,2]). The mid-infrared spectra of the samples and milk performance data were also recorded during routine milk recording and testing. The effects of breed, herd nested within breed, days in milk, season, milking period, age at calving, parity, and individual animal on the variation observed in MFG size were investigated. Breed, herd nested within breed, days in milk, season, and milking period significantly affected mean MFG size. Milk fat globule size was the largest at the beginning of lactation and subsequently decreased. Milk samples with the smallest MFG on average came from Holstein cows, and those with the largest were from Jersey and Brown Swiss cows. Partial least squares regression was used to predict MFG size from MIR spectra of samples with a calibration data set containing 2,034 and 2,032 samples for D[4,3] and D[3,2], respectively. Coefficients of determination of cross validation for D[4,3] and D[3,2] prediction models were 0.51 and 0.54, respectively. The associated ratio of performance deviation values were 1.43 and 1.48 for D[4,3] and D[3,2], respectively. With these models, individual mean MFG size could not be accurately predicted, but results may be sufficient to screen samples for having either small or large MFG on average. Significant but low correlations of D[4,3] and D[3,2] with milk fat yield were estimated (0.16 and 0.21, respectively). Significant and moderate Pearson correlation coefficients for fat percent with D[4,3] and D[3,2] were assessed (0.34 and 0.36, respectively). This correlation was greater between milk fat percentage and predicted MFG size than with measured MFG size with coefficients of 0.47 and 0.49 for D[4,3] and D[3,2], respectively. The MIR prediction equations are potentially overusing the correlation between fat and MFG size and exploiting the strong relationship between the MIR spectra and total milk fat. However, the predictions of MFG size are able to determine variation in mean globule size beyond what would be achieved just by looking at the correlation with fat production., (Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Dairy cattle evaluated for immune responses and identified as high responders are known to have a lower occurrence of economically important diseases, including mastitis, metritis, ketosis, and retained placenta. These high immune responders have also been shown to make more antibody following vaccination and to have improved milk and colostrum quality. Therefore, breeding for improved immune response is expected to have several benefits in the dairy industry. However, a concern of such an approach to improve animal health is the potential cost of lost production due to an allocation of host resources to mount a robust immune response. The objective of this study was to evaluate early- and late-lactation production parameters in cattle classified as having high, average, or low estimated breeding values (EBV) for cell-mediated (CMIR), antibody-mediated (AMIR), and overall immune responses. A total of 561 cows from 6 herds were phenotyped for immune response and ranked based on EBV for CMIR and AMIR. A linear animal model was used to evaluate differences in milk, fat, and protein yields among immune response groups, and a regression analysis was conducted based on immune response EBV. Overall, no difference in production parameters was found based on immune response rank; however, some positive relationships with immune response EBV were found, suggesting that breeding for enhanced immune responsiveness as a prophylactic approach to improve animal health would not come at the cost of lost production., (Copyright © 2016 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

The objective of this study was to evaluate IgG and β-lactoglobulin (β-LG) concentrations in colostrum and milk of Canadian Holsteins (n=108) classified as high (H), average (A), or low (L) for antibody-mediated (AMIR) or cell-mediated immune responses (CMIR) based on estimated breeding values. It was hypothesized that H-AMIR and H-CMIR cows produce colostrum (first milking) and milk (d 5 postcalving) with higher concentrations of IgG and β-LG. Data for IgG and β-LG in colostrum and milk were analyzed independently using mixed linear models. Least squares means were compared using Tukey's test. Cows classified as H-AMIR had higher IgG and β-LG concentrations in colostrum compared with A- and L-AMIR cows; 84% of H-AMIR, 69% of A-AMIR, and 68% of L-AMIR cows had over 5,000 mg/dL IgG in colostrum. No differences in IgG and β-LG concentrations in colostrum were noted among cows ranked on CMIR or in milk of cows ranked on AMIR. β-Lactoglobulin and IgG concentrations were positively correlated in colostrum. Breeding cows for H-AMIR status may reduce failure of passive transfer of IgG in their calves; β-LG may play a role in bovine immune defenses. Colostrum from H-AMIR cows may serve as a more economical feedstock source for manufacturing natural health products., (Copyright © 2016 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Background: Staphylococcus aureus is one of the most prevalent pathogens to cause mastitis in dairy cattle. Intramammary infection of dairy cows with S. aureus is often subclinical, due to the pathogen's ability to evade the innate defense mechanisms, but this can lead to chronic infection. A sub-population of S. aureus, known as small colony variant (SCV), displays atypical phenotypic characteristics, causes persistent infections, and is more resistant to antibiotics than parent strains. Therefore, it was hypothesized that the host immune response will be different for SCV than its parental or typical strains of S. aureus. In this study, the local and systemic immune protein responses to intramammary infection with three strains of S. aureus, including a naturally occurring bovine SCV strain (SCV Heba3231), were characterized. Serum and casein-depleted milk cytokine levels (interleukin-8, interferon-γ, and transforming growth factor-β1), as well as serum haptoglobin concentrations were monitored over time after intramammary infection with each of the three S. aureus strains. Furthermore, comparative proteomics was used to evaluate milk proteome profiles during acute and chronic phases of S. aureus intramammary infection., Results: Serum IL-8, IFN-γ, and TGF-β1 responses differed in dairy cows challenged with different strains of S. aureus. Changes in overall serum haptoglobin concentrations were observed for each S. aureus challenge group, but there were no significant differences observed between groups. In casein-depleted milk, strain-specific differences in the host IFN-γ response were observed, but inducible IL-8 and TGF-β1 concentrations were not different between groups. Proteomic analysis of the milk following intramammary infection revealed unique host protein expression profiles that were dependent on the infecting strain as well as phase of infection. Notably, the protein, component-3 of the proteose peptone (CPP3), was differentially expressed between the S. aureus treatment groups, implicating it as a potential antimicrobial peptide involved in host defense against S. aureus intramammary infection., Conclusions: Intramammary infection of dairy cattle with S. aureus causes an up-regulation of serum and milk immune-related proteins, and these responses vary depending on the infecting strain.

A recently isolated bovine Staphylococcus aureus small colony variant (SCV) was shown to persist within cultured endothelial cells. However, the clinical importance of S. aureus SCV in persistent infection of the mammary gland is unknown. The hypothesis tested here was a naturally occurring bovine S. aureus SCV, Heba3231, and a Newbould hemB mutant that was an artificially created SCV would establish mild intramammary infection and induce a different host response compared to their isogenic parental strains, 3231 and Newbould 305. Four groups of clinically healthy cows, 5 cows/treatment group, were infected by the intramammary route with SCV Heba3231, strain 3231, the hemB mutant or strain Newbould 305. Three quarters of the mammary gland of each cow were challenged with approximately 5000 colony-forming units of bacteria and the fourth quarter was infused with PBS. Cows were monitored and assigned clinical scores for the first 5 days post-challenge based on rectal temperature, appetite, milk yield, udder uniformity, milk appearance, bacterial culture of foremilk samples and somatic cell score (SCS). All cows were examined for chronic infection up to day 36 post-challenge. Cows challenged with SCV strains developed mastitis that was mild compared with that induced by the parent strains. Cows challenged with strain 3231 developed the most severe clinical mastitis. SCS from all treatment groups were significantly (P<0.05) higher at days 2-5 and 14-36 post-infection compared to day 0 before challenge. This milder host response to SCVs may represent an adaptation of S. aureus to the mammary gland environment.

Staphylococcus aureus is a common cause of bovine mastitis and foodborne and other diseases in humans. This study tested the hypothesis that small colony variants (SCVs) of S. aureus are implicated in chronic bovine mastitis. Six S. aureus isolates from foremilk samples from 11 chronically infected cows were investigated. Five isolates had typical morphology and were hemolytic and coagulase positive; one was a heterogeneous population of typical and SCV phenotype (tiny nonhemolytic colonies). In the presence of gentamicin, three of the previously typical S. aureus developed SCVs that were confirmed as S. aureus by biochemical and genetic analyses; these SCVs reverted to the typical form on antibiotic-free medium. The SCV isolate (Heba3231) from the heterogeneous population had a slow growth rate and prolonged lag phase and did not revert during 10 h of incubation. Transcriptional analysis showed that SCV Heba3231 had reduced expression of agr, hla, and coa and increased expression of indicators of fermentation pathways compared to the parent strain. Invasion of and persistence in a primary culture of bovine aortic endothelial cells (BAEC) showed that SCV Heba3231 had minimal deleterious effects, whereas the parent strain or the Newbould 305 strain caused severe damage. Recovery of the parent strain from BAEC yielded a mixture of the parent and SCV phenotypes. This study reports for the first time the isolation of S. aureus SCV from persistent bovine mastitis and suggests that SCV may be an important contributor to the prolonged survival of S. aureus in some cases of mastitis.

Suboptimal innate and immune mechanisms of host resistance during the peripartum period may contribute to increased incidence of mastitis. To evaluate associations between antibody response to ovalbumin and milk production during the peripartum period, 136 Holstein cows and heifers from three herds with known antibody response profiles, were evaluated for projected 305-d milk, protein, and fat yield. Using a previously described index (Wagter et al., 2000), cows were quantitatively classified based on their profile of antibody response to ovalbumin into high, average, or low antibody response groups. The single-effect antibody response group contributed significantly to variation in fat and protein yield, but not milk yield. The interaction between antibody response and parity significantly contributed to the variation in milk, fat, and protein yields; therefore the effects of group were reported on a within-parity basis. Among first-parity cows, low responders had a higher fat and protein yield than high or average antibody responder animals. Among older cows (parity 3 or greater) milk yield was significantly higher for those in the high antibody response group compared with average and low response groups. However, no significant differences in fat or protein yields were observed between high and low antibody response groups. These results suggest the possibility to select cows for enhanced immune response with no adverse effects on yield. That first-parity cows with low antibody response produce more fat and protein may be offset by the fact that mastitis occurrence was highest in this group in two out of three herds investigated. Selection for high immune response may prove beneficial to herd life by maintaining optimal yield, yet minimizing occurrence of disease.

Migration of leukocytes into the mammary gland is an essential element of resistance to infection which is likely influenced by expression of adhesion molecules. The contribution of subsets to mammary gland resistance remains unclear. Mononuclear cells from milk and blood of dairy cows were examined for variation in CD4+, CD8+, and WC1+ (Workshop Cluster 1; marker for gammadelta T cells) lymphocyte phenotypes and expression of LFA-1 and L-selectin at several time points during the periparturient period and at Week 16 of lactation. Proportions of CD4+ T cells were higher (p < or = 10.05) in blood than milk at all times between Week 0 and Week 16 relative to calving; the inverse was true of CD8+ cells. Expression of L-selectin was lower (p < or = 0.05) on CD4+ cells and higher on CD8+ cells from milk. The WC1+ subset was more frequent in blood than in milk except at calving when the opposite was true. After calving, proportions of L-selectin+ WC1+ cells decreased steadily to Week 16. Expression of LFA-1 was examined on mononuclear cell populations and found to be lower on milk cells and did not vary over time. We conclude that proportions of T cells subsets differ significantly between blood and milk, particularly around calving. Corresponding variations in L-selectin expression may indicate a role for this molecule in regulating the movement of CD8+ and WC1+ T cells into the bovine mammary gland.

Potential associations were investigated between bovine leucocyte antigen (BoLA) alleles and occurrence of disease. Cows (Holstein n = 835; Jersey n = 66) were examined for polymorphisms of the second exon of the BoLA-DRB3 gene, using the polymerase chain reaction (PCR), followed by digestion of the amplified fragments with three restriction endonucleases. Disease occurrences were recorded for each cow throughout one lactation. Milk somatic cell count data were retrieved through the Dairy Herd Improvement records and converted to somatic cell score (SCS). There were no effects of BoLA alleles on SCS in Jersey cows, but BoLA-DRB3.2*16 was significantly associated (P < or = 0.05) with lower SCS in Holsteins. Since the number of Jerseys was relatively small and prevalence of diseases in this population was low, health records of Jerseys were not analyzed further. BoLA associations with occurrence of disease in Holsteins were investigated using a log-linear model. There was a significant (P < or = 0.05) association between BoLA-DRB3.2*23 and occurrence of severe mastitis, from which coliforms were the most commonly isolated bacteria. The BoLA allele *3 was associated with a lower risk of retained placenta (P < or = 0.05) and alleles *16 (P < or = 0.05) and *22 (P < or = 0.05) with a lower risk of cystic ovarian disease. Although more studies are required to confirm the present findings, it can be concluded that BoLA alleles may have potential usefulness as genetic markers of higher or lower risk of disease occurrence in cows.