Mammary Health Research Articles

Chlorogenic acid mitigates heat stress-induced oxidative damage in bovine mammary epithelial cells by inhibiting NF-κB-mediated NLRP3 inflammasome activation via upregulating the Nrf2 signaling pathway.

Chlorogenic acid (CGA), a polyphenolic bioactive molecule derived from medicinal plants, is known for its strong antioxidant and anti-inflammatory properties. Previous studies have demonstrated that dietary supplementation with Lonicera japonica extract, rich in CGA, effectively enhances the production performance of lactating dairy cows under heat stress (HS) conditions. However, the molecular mechanisms underlying CGA's protective effects remain unclear. This study aims to elucidate the mechanisms by which CGA alleviates HS-induced oxidative damage in bovine mammary epithelial cells (bMECs), focusing on its pharmacological activity and potential application as a natural therapeutic agent for bovine mammary disorders. The results demonstrated that HS activates the NF-κB and NLRP3 signaling pathways by increasing ROS generation, leading to oxidative stress and inflammatory response in bMECs. CGA mitigates these effects by scavenging intracellular ROS, activating the Nrf2 signaling pathway, and inhibiting key molecules in the NF-κB and NLRP3 signaling pathways. This study provides new insights into the underlying molecular mechanisms of CGA's protective effects, highlighting its potential as a natural antioxidant for bovine mammary health and contributing to the broader application of polyphenolic compounds in managing oxidative stress and inflammation.

Serum macromineral dynamics and milk production of old Holstein cows submitted to a postpartum delayed milking strategy.

Lactation initiates with a massive Ca secretion into milk. Within 24-48 h post-calving, high-producing, older-parity dairy cows are highly susceptible to Ca disturbances. We hypothesized that the abrupt cessation of milking within this critical period would delay Ca secretion into milk, allowing lactating cows more time to stabilize their Ca homeostasis mechanisms and potentially lower the risk of blood Ca decline in the immediate postpartum period. After colostrum harvest, a total of 175 multiparous Holsteins (parity ranging from 3 to 7) were randomly assigned to three treatment groups: 1) control (n = 59), whereby cows were milked 3 times/day (M0), 2) the treatment whereby milking of cows was withdrawn for the first 24 h (M24; n = 60), and 3) for the first 48 h after calving (M48; n = 56). All cows were given two oral Ca boluses (31 g Ca/bolus), the first bolus was administered within 30-60 min after calving, and the second bolus was given 24 h later. After the delayed milking treatment, cows in M24 and M48 groups returned to M0 milking program. On d 2 and 3 post-calving, blood total Ca concentration was not different between M24 and M48 cows, but both groups had greater Ca concentrations than M0 cows. On day 2 post-calving, serum P concentration was greater in M48 compared to M24 and M0 (1.86 vs. 1.47 ± 0.06 mmol/L). On d 3, M0 cows had lower P concentration than M24 or M48 cows. Despite a transient decline in milk production in M24- and M48-treated cows, both treatments attained a similar milk production level as they switched to M0 milking program. No difference existed in the first 3 monthly test-day milk records. The postpartum milking strategy had no impact on the culling risk by 120 DIM. These results support delaying milking for 24 and 48 h after colostrum collection to maintain Ca status in multiparous cows. Evaluation of the long-term effects of the delayed milking strategies on mammary health, reproduction performance, and survivability of pluriparous dairy cows is recommended.

Prepartum Vaccination Against Neonatal Calf Diarrhea and Its Effect on Mammary Health and Milk Yield of Dairy Cows: A Retrospective Study Addressing Non-Specific Effects of Vaccination.

Prepartum vaccinations against neonatal calf diarrhea pathogens are administered in late pregnancy to provide passive immunity to calves through protective colostral antibodies. Potential non-specific effects of the vaccine on maternal innate immune responses and disease susceptibility during the sensitive transition period have not been addressed so far. In this retrospective study, data from 73,378 dairy cows on 20 farms in Germany were analyzed, using linear mixed-effects regression, quantile regression, and decision-tree-algorithms, to investigate the effects of prepartum vaccination on mammary health and milk yield by comparing non-vaccinated and vaccinated transition periods. Herd management-related factors were found to be most influential for mammary health and milk yield. Vaccinated cows were not significantly more likely to develop mastitis and did not have significantly different somatic cell counts and milk yields compared to non-vaccinated cows. Healthy primiparous cows with and without vaccination had similar energy-corrected milk yields. The study concludes that prepartum vaccination against calf diarrhea has no significant effects on mammary health and milk yield. Further research is recommended to investigate potential non-specific vaccine effects on other organ systems, infectious diseases, and production metrics of the dairy cow.

Assessment of mammary stress in early lactating crossbred (Alpine × Beetal) does during heat stress in conjunction with milk somatic cells and non-invasive indicators

Milk somatic cell counts (SCC) are crucial for monitoring dairy animals' mammary health and milk quality. This study was initiated to assess the mammary health of early lactating crossbred (Alpine × Beetal) does during periods of heat stress. The udder skin surface temperature (USST), total and differential milk SCC, milk composition, milk cortisol levels and phagocytic activity (PA) of milk neutrophils and macrophages were estimated in these does. Results indicated a significant (p<0.01) increase in the milk neutrophils to macrophages (N: M) ratio and milk cortisol levels with milk somatic cell score (SCS). The PA of milk neutrophils decreased significantly (p<0.01), while that of macrophages increased significantly (p<0.01) with higher SCC. On Pearson correlation, milk SCS revealed strong positive correlation (p<0.01) with N: M ratio (r=0.90), USST (r=0.98), milk cortisol (r=0.97), milk pH (r=0.83) and conductivity (r=0.92). Conversely, milk lactose exhibited a moderate negative correlation of (r= −0.48) with SCS. These findings suggest that USST infrared thermography and milk cortisol levels are promising non-invasive methods for rapidly assessing mammary stress in early lactating does during heat stress.

Draft genome sequences of 21 Bacillus sp. isolates from raw bovine milk.

Members of the Bacillus genus are commonly used as probiotics in livestock production. We isolated several Bacillus strains from healthy dairy cattle. The role of these strains in mammary health is of interest. Here, we present 21 draft genome assemblies and annotations of Bacillus sp. isolated from fresh raw milk.

Estimation of genetic parameters for production, composition and processability of milk from dairy sheep in a New Zealand flock

ABSTRACT This paper aimed to estimate the heritability and genetic correlations for processability (milk coagulation properties, cheese yield, and heat stability), milk production, and milk composition of dairy sheep in a New Zealand flock. Test-day records from 169 ewes were obtained during the 2021–2022 season. Heritability estimates for yield traits (milk, fat, protein, and lactose yield) were moderate and ranged from 0.33 to 0.38. Whereas heritability estimates for processability traits were lower and ranged from 0.17 to 0.27. The genetic correlations indicated that poorer milk coagulation properties were associated with lower mammary health indicated by higher SCS, higher pH, and lower lactose content. Additionally, a higher ratio of casein to calcium i.e. lower availability of soluble calcium was associated with poorer milk coagulation properties. Higher yields of milk, fat, protein, and lactose were associated, but to a smaller degree, with better MCP. It is proposed that genetic improvement of dairy sheep for higher yields of fat and protein, and for lower SCS, could indirectly improve milk processability for cheese-making. However, it is recommended that larger studies involving more dairy sheep flocks are conducted to validate the present results before developing a selection index for this industry.

Unveiling the regulatory role of SIRT1 in the oxidative stress response of bovine mammary cells

High-yield dairy cows typically undergo intense cellular metabolism, leading to oxidative stress in their mammary tissues. Our study found that compared with ordinary cows, these high-yield cows had significantly elevated levels of H2O2, lipoperoxidase, and total antioxidant capacity in their blood. This increased oxidative stress is associated with heightened expression of genes such as GCLC, GCLM, and SIRT1 and proteins such as SIRT1 in the mammary tissue of high-yield cows. We stimulated MAC-T cells with H2O2 at a concentration equal to the average H2O2 level in the serum of ethically high-yielding cows, as detected by an assay kit. Our observations revealed that short-term exposure (12 h) to H2O2 upregulated the expression of the SIRT1 gene and SIRT1 protein. It also increased gene expression for SOD2, CAT, GCLC, GCLM, PGC-1α, and NQO1, elevated the phosphorylation of AMPK, and enhanced protein expression of PGC-1α, NQO1, Nrf2, and HO-1, as well as reduced the phosphorylation of NF-κB. Additionally, short-term H2O2 stimulation resulted in increased total antioxidant capacity and levels of superoxide dismutase, glutathione, and catalase in the mammary epithelial cells of dairy cows. In contrast, prolonged exposure to H2O2 (24 h) yielded opposite results, indicating reduced antioxidant capacity. Further investigation showed that the SIRT1 inhibitor EX 527 could reverse the enhanced cellular antioxidant capacity triggered by short-term oxidative stress. However, it is crucial to note that although 12 h of H2O2 stimulation improved antioxidant capacity, reactive oxygen species (ROS) and malondialdehyde (MDA) levels inside the cell gradually increased over time, suggesting greater damage under long-term stimulation. Conversely, the SIRT1 activator SRT 2104 could reverse the reduced cellular antioxidant capacity caused by long-term oxidative stress and significantly inhibit the accumulation of ROS and MDA. Notably, SRT 2104 demonstrated similar effects in MAC-T cells during lactation. In summary, SIRT1 plays a crucial role in regulating the antioxidant capacity of mammary epithelial cells in dairy cows. This discovery provides valuable insights into the antioxidant mechanisms of mammary cells, which can serve as a theoretical foundation for future mammary health strategies.

Breast milk – a living superfood. Review of current knowledge

Introduction: Breastfeeding is considered the best nutrition for infants, including born preterm due to containing optimal ingredients for development and growth. Breast milk is a rich source of nutrients, it also contains diverse types of bacteria, which play a role in infant’s gastrointestinal tract colonization and preserving mammary health. Composition of human milk varies depending on numerous maternal and infant factors. Aim of the study: The aim of the study was to summarize the current knowledge about the content of nutrients, bioactive factors and microbiota diversity in human milk depending on various factors. Materials and methods: The work is a review of 26 mainly English-language scientific publications from 1989-2024 posted on the PubMed platform. Results: Milk composition changes in addition to several factors. Depending on postnatal age: preterm milk has higher content of protein, fat and immunological factors and lower concentration of lactose than term milk. Depending on milk maturity: Colostrum is higher in protein but lower in lactose, fat and energy than mature milk. Human milk is also a source of viable bacteria important for developing infant’s gut microbiota, but the diversity of bacterial strains in milk may vary. Depending on mode of delivery: milk of mothers after spontaneous labour contents more probiotic vaginal- and enteric-associated bacteria, while milk of mothers after C-section has more skin-associated microbiota. Depending on mother’s weight: milk of overweight mothers is lower in probiotic- and higher in pathogenic bacteria. Alcohol, nicotine, and some medications also have negative impact on produced milk. Conclusions: Human milk varies from woman to woman and its composition depends on several factors. Postnatal and gestational stage, delivery mode, mother's weight and certain substances have been found to be important factors influencing the constitution of breast milk, including nutrients, microbiota and volume of milk.

Correlation of udder thermogram and somatic cell counts as a tool for detection of subclinical mastitis in buffaloes.

This study aimed to monitor the mammary health of 37 multiparous Murrah buffaloes through infrared thermography (IRT). Based on the California Mastitis Test (CMT) and milk somatic cell counts (SCC), buffaloes were grouped into healthy (H, n = 16), subclinical mastitis (SCM, n = 10), and clinical mastitis (CM, n = 11). Buffaloes were milked twice daily in the morning (5:00-6:00 AM) and evening (5:00-6:00 PM). Rectal temperature and respiratory rates were recorded, CMT was performed and thermal images of the mammary gland of all the buffaloes were taken before and after each milking. Milk samples were analysed after each milking for SCC, fat, Solids-Not-Fat (SNF), density, protein, lactose, salts, conductivity, and pH immediately in the laboratory from fresh milk samples. The surface temperature of the periocular region of both the eyes, muzzle, flank, and vagina were also taken. Thermal images were used to assess the surface temperature of the udder (USST), teat apex (TAT), teat barrel (TB1T), teat base (TB2T), and teat skin surface (TSST). Eye and USST showed significantly higher temperatures (p < 0.05), whereas skin surface temperatures (SST) of different body parts were non-significant in both SCM and CM animals than buffaloes in the H group. Milk SCC showed a positive correlation with conductivity (r > 0.7), salts, and pH (r < 0.6) and a negative correlation with fat, SNF, density, protein, and lactose. TAT, TB1T, TB2T, TSST, and USST were positively correlated with milk SCC. Receiver Operating Characteristic (ROC) analysis of H and SCM groups showed that USST before milking had optimum sensitivity (Se = 0.80) and specificity (Sp = 0.906) among the various skin temperatures recorded. Thermal images captured during the morning showed higher sensitivity compared to images taken in the evening. Results indicate IRT can be used to monitor the mammary health of buffaloes but using IRT in conjunction with milk SCC can help in the accurate prediction of SCM in dairy buffaloes.

Effect of subclinical mastitis on milk taurine concentration in dairy cows

The objective of this study was to evaluate whether taurine has any role in bovine subclinical mastitis, and the relationship between milk taurine concentration and somatic cell count. Forty milk samples from dairy cows aged 3 to 6 during lactation were used for this research. The California Mastitis Test (CMT) and somatic cell counts (SCC) were determined in the diagnosis of subclinical mastitis. The subclinical mastitis group consisted of 20 milk specimens positive for CMT and SCC&gt;200.000/ml of milk. The control group consisted of 20 milk specimens negative for CMT and SCC&lt;200.000/ml of milk. A bovine-specific taurine enzyme-linked immunosorbent assay kit was used to determine the taurine concentration in the milk. The milk serum taurine concentrations were determined as 232.1±89.8 pg/ml in the control group and 158.0±55.6 pg/ml in the subclinical mastitis group. These results determined that the taurine concentration in milk with subclinical mastitis decreased approximately 1.5 times compared to healthy milk (P&lt;0.05). A significant negative correlation was determined between the taurine concentration in cow’s milk with subclinical mastitis and the number of somatic cells (r= -0.933; P&lt;0.001). From the findings of this study, it was concluded that both somatic cell counts and the measurement of taurine in cow’s milk could be used to monitor mammary health.

Roles of MAPK and Nrf2 signaling pathways in quercetin alleviating redox imbalance induced by hydrogen peroxide in mammary epithelial cells

Abstract Oxidative stress is a risk factor for mammary health, resulting in decreased milk yield and milk quality. Application of exogenous bioactive compounds has been a research focus of antioxidation of animals in the mammary gland. Quercetin is a flavonoid extracted from vegetables, fruits and tea and has been shown to have a variety of biological activities, but the effect of quercetin on redox imbalance in mammary epithelial cells is unclear. In this study, cells of HC11, a mouse mammary epithelial cell line, were treated with quercetin, and the effects and molecular mechanisms of quercetin protection on hydrogen peroxide-induced oxidative stress were studied. Results showed that 20 μΜ quercetin attenuated hydrogen peroxide-induced lactate dehydrogenase release and reactive oxygen species (ROS) accumulation and alleviated the reduction of cell viability and antioxidant capacity. Quercetin significantly restored the activation of mitogen-activated protein kinase (MAPK) and nuclear factor E2-related factor 2 (Nrf2) pathways induced by hydrogen peroxide. Importantly, the inhibitors of p38 MAPK and extracellular regulated protein pathways affected the activation of Nrf2 pathway. All inhibitors of MAPK and Nrf2 pathways reduced the protective effects of quercetin on cell proliferation, the activity of catalase and the expression of glutamate-cysteine ligase modifier subunit. Meanwhile, the effects of quercetin on the production of ROS and expression of glutamate/cystine reverse transporter light chain were mainly dependent on Nrf2 pathway. In summary, the protective effect of quercetin in mammary epithelial cells was mediated via MAPK and Nrf2 pathways.

Analysis of the Somatic Cell Pattern in Mastitis - Affected Cows on Three Dairy Farms in Vojvodina

Summary Somatic cells (SCs) in milk, which include epithelial cells from the gland and blood cells, are present in milk during the normal course of milking. Increase in SCs is found in mastitis-affected dairy cows and can be a useful indicator for estimating mammary health and milk quality worldwide. The aim of this study was to determine whether there was a pattern of somatic cell count (SCC) in mastitis-affected cows on three different farms. The study was conducted on three dairy farms of high milk-producing cattle breeds in Vojvodina during 2021. Samples were taken from 15 cows from each farm, all of the cows being diagnosed with clinical and subclinical mastitis. The SCC in milk samples was determined by the microscopic reference method according to the standard (SRPS EN ISO 13366-1:2010) of the Institute for Standardization of Serbia. The value of SCC was considered as high if &gt;200.000 cells/mL, as this is the threshold indicating secretion disorder. In order to examine the differences between the observed three farms, one-factor analysis of variance (ANOVA) was applied, while a post-hoc LSD test was used for determination of statistically significant differences between the SCC in cows on three different farms. The mean values of the SCC on Farms 1, 2 and 3 were 7,055,266.67, 2,619,893.33 and 552,000 cells/mL, respectively. Based on the results, a statistically significant difference (p&lt;0.05) was established between Farms 1 and 2, as well as between Farms 1 and 3, while there was no statistically significant difference between Farms 2 and 3. Apart from mastitis, differences in the SCC on the farms could also be influenced by the cows’ productivity, parity, lactation stage and breed, as well as poor management practices. Besides mastitis control, better hygiene and proper nutrition can help in reducing SCs in milk. In conclusion, establishing SCs pattern can provide useful information that may contribute to reducing SCs and developing differential SCs standards to help obtain milk with low SCs and consequently better dairy products with a longer shelf life.

Genetic correlations of direct and indirect genetic components of social dominance with fitness and morphology traits in cattle

BackgroundWithin the same species, individuals show marked variation in their social dominance. Studies on a handful of populations have indicated heritable genetic variation for this trait, which is determined by both the genetic background of the individual (direct genetic effect) and of its opponent (indirect genetic effect). However, the evolutionary consequences of selection for this trait are largely speculative, as it is not a usual target of selection in livestock populations. Moreover, studying social dominance presents the challenge of working with a phenotype with a mean value that cannot change in the population, as for every winner of an agonistic interaction there will necessarily be a loser. Thus, to investigate what could be the evolutionary response to selection for social dominance, it is necessary to focus on traits that might be correlated with it. This study investigated the genetic correlations of social dominance, both direct and indirect, with several morphology and fitness traits. We used a dataset of agonistic contests involving cattle (Bos taurus): during these contests, pairs of cows compete in ritualized interactions to assess social dominance. The outcomes of 37,996 dominance interactions performed by 8789 cows over 20 years were combined with individual data for fertility, mammary health, milk yield and morphology and analysed using bivariate animal models including indirect genetic effects.ResultsWe found that winning agonistic interactions has a positive genetic correlation with more developed frontal muscle mass, lower fertility, and poorer udder health. We also discovered that the trends of changes in the estimated breeding values of social dominance, udder health and more developed muscle mass were consistent with selection for social dominance in the population.ConclusionsWe present evidence that social dominance is genetically correlated with fitness traits, as well as empirical evidence of the possible evolutionary trade-offs between these traits. We show that it is feasible to estimate genetic correlations involving dyadic social traits.

Taurine alleviates heat stress-induced mammary inflammation and impairment of mammary epithelial integrity via the ERK1/2-MLCK signaling pathway

Heat stress leads to milk production losses and mammary gland inflammation, which may be associated with mammary epithelium damage. Taurine is one of the most abundant free amino acids in mammals which has anti-inflammatory properties. This study aimed to explore the effect of taurine pretreatment on heat stress-induced mammary epithelial integrity disruption and inflammatory damage. In our first experiment on dairy cows our results showed that compared with animals under autumn thermoneutral condition (THI = 62.99 ± 0.71), summer heat stress (THI = 78.01 ± 0.39) significantly reduced milk yield and disrupted mammary epithelial integrity as revealed by increased concentrations of serotonin and lactose in plasma, and increased levels of SA and Na+/K+ in milk. In our second study, 36 lactating mice were randomly divided into three groups (n = 12) for a 9d experiment using a climate chamber to establish a heat stress model. Our findings suggest taurine pretreatment could attenuate heat stress-induced mammary histopathological impairment, inflammation response, and enhance mammary epithelium integrity, which was mainly achieved by promoting the secretion of ZO-1, Occludin, and Claudin-3 through inhibiting activation of the ERK1/2-MLCK signaling pathway in the mammary gland. Overall, our findings indicated that heat stress induced mammary epithelium dysfunction in dairy cows, and emphasized the protective effect of taurine on mammary health under heat stress conditions using a mouse model, which may be achieved by alleviating the mammary epithelium integrity damage and inflammation response.

O-180 Sheep habit during hand milking, and relations between the incorrect hand milking procedure and mammary health

O-180 Sheep habit during hand milking, and relations between the incorrect hand milking procedure and mammary health

Blood neutrophil extracellular traps: a novel target for the assessment of mammary health in transition dairy cows

BackgroundMammary health is important for transition dairy cows and has been well recognized to exert decisive effects on animal welfare. However, the factors influencing mammary health are still unclear. Differential somatic cell count (DSCC) could reflect the mastitis risk since it is the percentage of neutrophils plus lymphocytes in total somatic cells and could be reflective of mammary health of dairy cows. This work aimed to investigate the assessment and prognosis of the health of transition cows based on blood neutrophil extracellular traps (NETs).ResultsEighty-four transition Holstein dairy cows were selected. The serum was sampled in all the animals at week 1 pre- and postpartum, and milk was sampled at week 1 postpartum. Based on the DSCC in milk at week 1, cows with lower (7.4% ± 4.07%, n = 15) and higher (83.3% ± 1.21%, n = 15) DSCCs were selected. High DSCC cows had higher levels of red blood cell counts (P < 0.05), hemoglobin (P = 0.07), and hematocrit (P = 0.05), higher concentrations of serum oxidative variables [(reactive oxygen species (P < 0.05), malondialdehyde (P < 0.05), protein carbonyl (P < 0.05), and 8-hydroxy-2-deoxyguanosine (P = 0.07)], higher levels of serum and milk NETs (P < 0.05) and blood-milk barrier indicators, including serum β-casein (P = 0.05) and milk immunoglobulin G2 (P = 0.09), than those of low DSCC cows. In addition, lower concentrations of serum nutrient metabolites (cholesterol and albumin) (P < 0.05) and a lower level of serum deoxyribonuclease I (P = 0.09) were observed in high DSCC cows than in low DSCC cows. Among the assessments performed using levels of the three prepartum serum parameters (NETs, deoxyribonuclease I and β-casein), the area under the curve (0.973) of NETs was the highest. In addition, the sensitivity (1.00) and specificity (0.93) were observed for the discrimination of these cows using NETs levels with a critical value of 32.2 ng/mL (P < 0.05).ConclusionsThe formation of NETs in blood in transition dairy cows may damage the integrity of the blood-milk barrier and thereby increase the risk for mastitis in postpartum cows.

Sodium and Potassium Concentrations and Somatic Cell Count of Human Milk Produced in the First Six Weeks Postpartum and Their Suitability as Biomarkers of Clinical and Subclinical Mastitis.

The sodium (Na) concentration and the ratio of Na to potassium (K; Na/K) in human milk are used commonly as biomarkers of subclinical mastitis, but limited data exist on their relationship to and ability to predict clinical mastitis. Here, we assessed concentrations of Na, K, Na/K, and somatic cell count (SCC), a mammary health biomarker used in the dairy industry, in milk prospectively collected from both breasts of 41 women over the first 6 weeks postpartum. Although values differed over time postpartum, there were no differences in mean values between breasts. Nearly one-quarter (24%) of participants experienced clinical mastitis. Somatic cell counts >4.76 × 105 cells/mL were most strongly related to development of clinical mastitis in the following week (odds ratio, 7.81; 95% CI, 2.15−28.30; p = 0.002), although relationships were also observed for SCC > 4.00 × 105 cells/mL and Na concentration >12 mmol/L. Estimates of the prevalence of subclinical mastitis in women who never progressed to clinical mastitis differed by biomarker but ranged from 20 to 75%. Despite these findings, positive predictive values (PPV) of the biomarkers for identifying clinical mastitis were low (≤0.34), indicating additional research is needed to identify single biomarkers or composite measures that are highly specific, sensitive, and predictive of clinical mastitis in women.

22 Young Scholar Talk PHD: Investigating Ovine Mastitis: Microbial Sources and Management Methods to Reduce the Prevalence

Abstract Subclinical mastitis, a common intramammary disease in sheep production, can be costly to producers due to compromised performance and decreased longevity. Our research focused on preventative and therapeutic measures on mammary health where the objectives were to identify (1) the impact of Zn supplementation on the milk microbiome and (2) the impact of management practices at lambing and weaning on prevalence and cure rate of subclinical mastitis, the milk microbiome, and levels of antimicrobial resistance in milk bacteria. In study 1, the milk microbiome was characterized during the first 3 wk of lactation and at weaning in ewes divergent in dietary Zn supplementation (1× = CON or 3× recommendations = ZnTRT). Mammary health was assessed using somatic cell count (SCC) class. Amplicon sequencing revealed the presence of Staphylococcus, Mannheimia, Corynebacterium, and Pseudomonas, all major mastitis pathogens. Effects of breed, dietary Zn concentration, and SCC class on diversity were limited to early lactation, where CON milk had greater composition stability than ZnTRT milk (P = 0.02). In study 2, milk bacteria were characterized by culture; Staphylococcus spp. and Streptococcus spp. were tested for antimicrobial susceptibility. Subclinical mastitis prevalence ranged from 22–66% where coagulase-negative staphylococci (CoNS; 59%), bacilli (35%), Mannheimia haemolytica (10%), S. aureus (8%), streptococci (5%), and Corynebacterium spp. (5%) were common. Milk samples were compared by jug bedding treatment: jugs were cleaned and dried with barn lime before adding fresh straw (CLEAN) or fresh straw was added atop soiled bedding (SOILED). Bedding had no effect on subclinical mastitis (P = 0.57), but CoNS had greater sulfadimethoxine resistance in SOILED isolates (P = 0.03). Additional mastitis control methods at weaning were evaluated: penicillin injection (PENN), restricted feed access (FAST), or their combination (COMBO). Weaning treatment did not affect cure rate from weaning to 3-d post- weaning (P = 0.21). Further characterization of these samples via microbial sequencing are underway with source tracking analyses to investigate an exogenous route via retrograde transfer and environmental bacteria or endogenous route via an entero-mammary pathway. Results support that breed, animal husbandry, and mammary health variably affect the milk microbiome and provide novel insight to the impact of management practices in a milk microbiome longitudinal study.

Genetic correlations and causal effects of fighting ability on fitness traits in cattle reveal antagonistic trade-offs

Complex genetic and phenotypic relationships are theorized to link different fitness components but revealing the correlations occurring among disparate traits requires large datasets of pedigreed populations. In particular, the association between traits beneficial to social dominance with health and fitness could be antagonistic, because of trade-offs, or positive, because of greater resource acquisition by dominant individuals. Studies investigating these relationships found some empirical evidence in support of both theories, mainly using multiple trait models (MTM). However, if a trait giving a social advantage is suspected to affect the expression of other traits, MTM could provide some bias, that structural equation models (SEM) could highlight. We used Aosta Chestnut-Black Pied cattle to investigate whether the fighting ability of cows (the capability of winning social dominance interactions) is genetically correlated with health and fitness traits. We ran both MTM and SEM using a Gibbs sampling algorithm to disentangle the possible causal effects of fighting ability from the genetic correlations that this trait shares with other traits: individual milk yield, somatic cells (representing mammary health), fertility, and longevity. We found antagonistic genetic correlations, similar under both approaches, for fighting ability vs. milk, somatic cells, and fertility, Accordingly, we found only a slight causal effects of fighting ability on these traits (–0.012 to 0.059 in standardized value). However, we found genetic correlations opposite in sign between fighting ability and longevity under MTM (0.237) and SEM (–0.183), suggesting a strong causal effect (0.386 standardized) of fighting ability on longevity. In other words, MTM found a positive correlation between longevity and fighting ability, while SEM found a negative correlation. The explanation could be that for economic reasons dominant cows are kept in this population for longer, thus attaining greater longevity: using MTM, the economic importance of competitions probably covers the true genetic correlation among traits. This artificially simulates a natural situation where an antagonistic genetic correlation between longevity and fighting ability appears positive under MTM due to a non-genetic advantage obtained by the best fighters. The use of SEM to properly assess the relationships among traits is suggested in both evolutionary studies and animal breeding.

Characterization of rumen, fecal, and milk microbiota in lactating dairy cows.

Targeting the gastrointestinal microbiome for improvement of feed efficiency and reduction of production costs is a potential promising strategy. However little progress has been made in manipulation of the gut microbiomes in dairy cattle to improve milk yield and milk quality. Even less understood is the milk microbiome. Understanding the milk microbiome may provide insight into how the microbiota correlate with milk yield and milk quality. The objective of this study was to characterize similarities between rumen, fecal, and milk microbiota simultaneously, and to investigate associations between microbiota, milk somatic cell count (SCC), and milk yield. A total of 51 mid-lactation, multiparous Holstein dairy cattle were chosen for sampling of ruminal, fecal, and milk contents that were processed for microbial DNA extraction and sequencing. Cows were categorized based on low, medium, and high SCC; as well as low, medium, and high milk yield. Beta diversity indicated that ruminal, fecal, and milk populations were distinct (p < 0.001). Additionally, the Shannon index demonstrated that ruminal microbial populations were more diverse (p < 0.05) than were fecal and milk populations, and milk microbiota was the least diverse of all sample types (p < 0.001). While diversity indices were not linked (p > 0.1) with milk yield, milk microbial populations from cows with low SCC demonstrated a more evenly distributed microbiome in comparison to cows with high SCC values (p = 0.053). These data demonstrate the complexity of host microbiomes both in the gut and mammary gland. Further, we conclude that there is a significant relationship between mammary health (i.e., SCC) and the milk microbiome. Whether this microbiome could be utilized in efforts to protect the mammary gland remains unclear, but should be explored in future studies.