Ruminants

The gastrointestinal microbiota plays a key role in the health and productivity of llama crias, yet its dynamics under disease conditions remain poorly understood. This study aimed to characterize and compare the fecal microbiota of healthy and diseased llama crias. Fecal samples collected from nine llama crias (six with diarrhea and three clinically healthy controls) were analyzed using 16S rRNA gene sequencing targeting the V4 region, followed by bioinformatic processing and statistical analyses, including diversity metrics and generalized linear mixed models. Results showed that microbial communities were dominated by Bacillota and Bacteroidota in both groups; however, diseased animals exhibited increased abundance of Pseudomonadota, particularly Gammaproteobacteria and Enterobacteriaceae. Beta diversity analysis revealed significant differences in community structure between groups, with diseased samples showing higher dispersion. Additionally, a greater number of unique ASVs was observed in diseased individuals, indicating increased microbial heterogeneity. Differential abundance analysis identified distinct microbial signatures associated with health status, with opportunistic taxa enriched in diseased animals and fiber-degrading taxa more prevalent in healthy individuals. Overall, the findings demonstrate an association between diarrhea and differences in the fecal microbiota of llama crias. Because this was a cross-sectional observational study, causal relationships cannot be inferred. These results provide a foundation for future investigations into host–microbiota interactions and gastrointestinal health in South American camelids. Full article

This study evaluated the effect of limiting feed intake to 92% of ad libitum for 28 or 56 d of a 56 d finishing period on growth performance, carcass characteristics, and visceral organ mass in wethers. Thirty Polypay wethers (initial SBW = 25.6 ± 5.27 kg; 15 pens, 2 lambs/pen) were blocked by body weight and assigned to three treatments: ad libitum intake for 56 d (CON), 92% of ad libitum intake for 28 d and then ad libitum intake for 28 d (28L), or 92% of ad libitum intake for 56 d (56L). Cumulatively, DMI decreased as restriction length increased (p < 0.001), but the final SBW, ADG, and G:F did not differ between treatments (p ≥ 0.11). Hot and cold carcass weights along with carcass muscle and bone masses were lesser in 28L than CON, but 56L did not differ (p ≤ 0.04). Carcass fat mass was greatest in CON and least in 28L (p ≤ 0.04). Relative to EBW, liver mass was greatest in 28L and least in 56L (p = 0.03). Limit feeding for 56 d maintained carcass weight while increasing leanness compared to CON, whereas a 28 d restriction period reduced carcass and muscle mass, possibly due to visceral organ recovery. Full article

Accurate live-weight monitoring is important for calf management, but calibrated scales are not always available under farm conditions. This study evaluated the accuracy of a thoracic measuring tape for estimating live weight in Minhota calves and examined whether tape error was influenced by age, sex and dam parity. The dataset included 210 repeated weighing records from 68 biologically distinct calves. Scale-measured live weight was used as the reference value, and tape accuracy was assessed using signed error, absolute error, percentage error, absolute percentage error, correlation and Bland–Altman analysis. Repeated-measures regression models were used to account for multiple records from the same calf. Tape-estimated live weight was very strongly correlated with scale-measured live weight (r = 0.997). The tape showed a small average underestimation of live weight, with a mean signed error of −3.02 kg, mean absolute error of 7.79 kg, root mean squared error of 11.92 kg and mean absolute percentage error of 4.97%. Age was the main factor associated with tape accuracy. For every additional 100 days of age, signed error decreased by 5.74 kg, indicating increasing underestimation in older calves. Sex and dam parity had limited effects. The thoracic measuring tape is a useful practical tool for routine monitoring of Minhota calf growth, but age-related bias should be considered, especially in older and heavier calves. Full article

The growing demand for high-quality beef has driven the selection of bovine genotypes offering superior marbling and tenderness. This study evaluated meat quality parameters in heifers from four Nellore-based genetic groups: ½ Aberdeen Angus × ½ Nellore (AN), ½ Japanese Brown × ½ Nellore (BN), ½ Japanese Brown × ¼ Aberdeen Angus × ¼ Nellore (TriBAN), and ½ Japanese Black × ¼ Aberdeen Angus × ¼ Nellore (TriJAN). Thirty-two heifers (eight/group) were finished in commercial feedlots. Samples of the longissimus thoracis muscle were analyzed for physical attributes (pH, cooking loss, shear force, marbling, water retention capacity, and colour), chemical composition, and fatty acid profile. In addition, animal performance (daily gain and final weight) was determined. A completely randomized design was used with analysis of variance followed by Tukey’s test (α = 0.05). The AN group showed the greatest final weight and daily gain (p < 0.01). There were no significant differences among genetic groups for pH, cooking loss, shear force, marbling, water-holding capacity, or colour (p > 0.05). Across all groups, the mean ultimate pH was 5.59, shear force (WBSF) averaged 41.11 N, and intramuscular fat (ether extract) content averaged 13.15 g 100 g⁻¹, indicating desirable technological and eating-quality characteristics. Most fatty acids did not differ among treatments (p > 0.05), except for arachidonic acid (C20:4 n-6), which was present at higher concentrations (p < 0.05) in the TriBAN group than in the other genetic groups. In conclusion, despite differences in productive performance, all genotypes produced meat with consistent quality traits, including tenderness, marbling, and fatty acid profiles associated with high-quality beef. Full article

This study comprised two related experiments. Experiment 1 evaluated the effects of low-temperature long-time pasteurization (LTLT, 63 °C for 30 min) on selected vitamins in bovine colostrum and mature milk. Experiment 2 independently evaluated the effects of dietary β-carotene supplementation on growth performance, fecal scores, oxidative status, cortisol concentrations, and fecal microbiota in preweaning calves. In Experiment 1, colostrum and mature milk were collected from four primiparous and four multiparous Holstein cows before and after LTLT. Concentrations of vitamin A, β-carotene, vitamin B1, vitamin B2, vitamin B9, and vitamin B12 were determined. In Experiment 2, 128 neonatal Holstein heifer calves were randomly assigned to a control group or a β-carotene-supplemented group (100 mg/day/calf) for 56 days. Growth performance, fecal scores, serum antioxidant indicators, cortisol concentrations, and fecal microbiota were evaluated. Colostrum contained substantially higher β-carotene concentrations than mature milk, particularly in primiparous cows (p < 0.001). LTLT reduced β-carotene concentrations by 30% in colostrum(p = 0.034) and significantly decreased vitamin B1 (p < 0.001), whereas the remaining vitamins were only minimally affected. Dietary β-carotene supplementation stabilized antioxidant enzyme activities, reduced serum malondialdehyde and cortisol concentrations (p < 0.001), decreased the occurrence of severe diarrhea (p = 0.046), increased the relative abundance of Blautia, and reduced Fusobacterium and Parabacteroides. Average daily gain did not differ between treatments (p = 0.154). Under the conditions evaluated in Experiment 1, β-carotene was the vitamin most affected by LTLT in colostrum. In the separate feeding experiment, dietary β-carotene supplementation affected several antioxidant indicators, reduced cortisol concentrations and the frequency of severe diarrhea scores, and altered fecal microbial composition, but did not affect average daily gain. Full article

Most studies involving genomic data in animal breeding use only the effects of autosomal chromosome markers, excluding the sex chromosomes. However, the X chromosome is the second-largest chromosome in the bovine genome, and several economically important traits are sexually dimorphic, such as those related to growth. Therefore, the objective of this study was to evaluate whether there are predictive advantages for genetic parameters when including genomic markers from the X chromosome for yearling weight (YW) and postweaning gain (PWG) in Nellore cattle. Genetic parameter estimates were obtained under three scenarios: (1) only pedigree and phenotypic information; (2) pedigree, phenotypes, and autosomal chromosome markers; and (3) pedigree, phenotypes, autosomal chromosome markers, and X chromosome markers. Analyses were carried out using Bayesian inference with BLUPF90 family software version 2025. The heritability estimates obtained and their respective standard errors were 0.41 ± 0.004 for YW and 0.21 ± 0.004 for PWG. No differences were observed among the three scenarios tested for either trait. Therefore, the inclusion of the X chromosome did not influence the estimates of genetic parameters for these growth traits in Nellore cattle. Nevertheless, further molecular and genomic studies on the bovine X chromosome are still needed to explain the genetic effects and biological functions associated with this chromosome and with different traits of economic interest, as well as to justify whether to include the X chromosome in genomic prediction analyses. Full article

This review used a qualitive approach to help further understand the benefits of pregnancy shearing and its potential mechanisms. A recent meta-analysis showed that pregnancy shearing increased lamb birth weight when conducted between days 42 and 100 of gestation but not after day 100; however, there was no effect on lamb weaning weight. Factors identified as potential mechanisms for the lamb birth weight response include comb type, gestation length, ewe pregnancy nutrition and feed intake, changes in ewe hormones and metabolites and altered placental development. There was, however, no single consistent parameter identified for the birth weight effect and more research is required. Shearing can potentially increase lamb survival, thermoregulatory capability and improve behaviour and ewe milk production but, again, further research is also required to confirm these. In conclusion, to maximise the chance of a birth weight response, farmers should focus on twin-bearing ewes of adequate body condition, shear with a comb that leaves a greater stubble depth and ensure ewes are offered at least pregnancy maintenance feeding levels. Full article

This study investigated whether miR-31-5p abundance in fresh Holstein bull semen is associated with post-thaw sperm resilience. The initial cohort comprised 36 Holstein bulls, from which 16 ejaculates representing the highest- and lowest-ranking post-thaw freezers were selected for epigenetic and molecular analyses. Fresh semen was analyzed for miR-31-5p, while BAX and BCL2 were evaluated at transcript and protein levels before and after cryopreservation. Post-thaw sperm quality was assessed using total motility, viability, JC-1 mitochondrial membrane potential, Annexin-negative spermatozoa, reactive oxygen species (ROS) and sperm DNA fragmentation. Cryopreservation significantly impaired sperm quality, increased ROS and DNA fragmentation, and shifted the molecular profile toward increased BAX and reduced BCL2. Ejaculates with superior post-thaw motility showed higher miR-31-5p levels, accompanied by better preservation of viability, mitochondrial function, non-apoptotic membrane status, lower ROS burden and DNA fragmentation after thawing. Fresh miR-31-5p was positively associated with post-thaw motility, viability, mitochondrial function, and Annexin-negative spermatozoa and negatively associated with post-thaw ROS. Our data support miR-31-5p as a potential candidate biomarker of sperm freezability in Holstein bulls. Full article

The objective of this study was to evaluate the effects of corn processing method (ground corn, GC, vs. steam-flaked corn, SFC) and daily calcium propionate (CaPr; 0 vs. 9.45 g/lamb/d) supplementation on productive performance, dietary energetics, fat deposition, and carcass characteristics in finishing lambs. Thirty-six Dorper × Katahdin lambs (44.95 ± 3.30 kg initial body weight, IBW), blocked by IBW and randomly assigned within block to a 2 × 2 factorial arrangement, were used. Diets contained 50% corn grain and treatments consisted of: (1) GC, (2) SFC, (3) GC plus CaPr, and (4) SFC plus CaPr. There were no corn processing × CaPr interactions for growth performance, dietary energetics, or observed-to-expected dietary net energy (NE) ratios. Steam-flaked corn decreased DMI (1.30 vs. 1.35 kg/d; p = 0.0036) and increased average daily gain (ADG; 0.168 vs. 0.144 kg/d), gain-to-feed ratio (G:F), and observed-to-expected dietary NE ratios compared with GC diets (p < 0.05). In contrast, CaPr supplementation increased DMI (1.35 vs. 1.30 kg/d; p = 0.0215) without affecting ADG, G:F, or observed-to-expected dietary NE ratios (p > 0.05). Steam-flaked corn increased hot carcass weight (p = 0.0339), cold carcass weight (p = 0.0241), Longissimus lumborum muscle area (p = 0.0206), and chest depth (p = 0.0368), whereas CaPr increased carcass length (p = 0.0451). Interactions between corn processing and CaPr supplementation were observed for rib fat thickness (p = 0.0491), rump fat thickness (p = 0.0272), visceral fat (p = 0.0485), perirenal fat (p = 0.0209), and shoulder tissue composition, including muscle (p = 0.0309), fat (p = 0.0438), and muscle:fat ratio (p = 0.0348). In GC diets, CaPr supplementation decreased fat deposition and increased muscle proportion, whereas in SFC diets CaPr supplementation increased fat deposition and reduced muscle proportion. Neither corn processing nor CaPr supplementation affected visceral mass (g viscera/g empty body weight). Calcium propionate supplementation decreased hindquarter yield (p = 0.0494), increased shoulder IMPS207 yield (p = 0.0494), and increased purge loss at 24 h (p = 0.0496). Water-holding capacity showed a corn processing × CaPr interaction (p = 0.0170), whereas the remaining meat-quality variables were not affected. Overall, SFC improved productive performance and dietary energy utilization, whereas CaPr increased DMI and altered fat deposition and tissue composition responses depending on corn processing method. Full article

Major fecundity (Fec) genes play a central role in regulating the ovulation rate and litter size in sheep and have become important targets for genetic improvement programs. This study aimed to systematically evaluate the global evidence regarding the association of the major fecundity genes BMPR1B, BMP15, and GDF9 with litter size through a systematic review and meta-analysis. A total of 104 studies met the eligibility criteria for the systematic review, 31 of which provided sufficient quantitative data for meta-analysis. Random-effects models were used to compare litter size among genotypes, and subgroup analyses together with meta-regression were performed to investigate the contribution of gene identity, mutation type, climatic region, and production system to the observed between-study heterogeneity. Overall, heterozygous carriers of fecundity-associated polymorphisms produced significantly larger litters than wild-type animals. Gene-specific analyses showed that BMPR1B exhibited the strongest positive association with litter size, followed by BMP15, whereas GDF9 showed no significant overall pooled effect. Meta-regression identified gene identity (Pseudo-R² = 38.57%) and mutation type (Pseudo-R² = 31.12%) as the principal sources of between-study heterogeneity, while climatic region and production system had no significant moderating effects. These findings provide robust quantitative evidence supporting the use of validated fecundity-associated markers, particularly BMPR1B, in marker-assisted and genomic selection programs aimed at improving reproductive performance in sheep. Full article

Grape pomace represents the main by-product generated during winemaking and is characterised by its richness in polyphenols, dietary fibre, residual sugars, lipids, and triterpenes. These bioactive compounds derived from grapes are known to positively influence oxidative status, metabolic balance, and animal productivity, positioning grape pomace as a promising, environmentally and economically sustainable alternative feed ingredient for conventional feed components. This research evaluated the effects of incorporating different inclusion rates (0, 6, 12, and 18% DM) of ensiled red grape pomace (RGP) into isoenergetic and isoproteic diets on the nutritional and technological characteristics of goat milk. Seventy-two Murciano-Granadina dairy goats were selected and distributed into eight homogeneous groups (n = 9 per group) based on physiological traits. Each diet was randomly assigned to two groups, and the feeding trial extended over eight weeks. After a two-week adaptation to the experimental diets, four biweekly milk samplings were performed to obtain representative bulk tank samples from each treatment group. Milk samples were analysed for gross composition, pH, mineral profile, fatty acid composition, coagulation properties, colourimetric parameters, and antioxidant capacity. The collected data were analysed using a general linear model, considering the effect of the treatment, sampling days, and their interaction (Proc. GLM, SAS v9.4). Dietary RGP inclusion had no significant effect on milk gross composition or on the antioxidant activity of the milk. However, it led to a significant reduction in milk urea content and somatic cell count, alongside improvements in the lipid profile from a human health perspective. The magnitude of the effects observed in the colourimetric parameters (<0.5 units) fell below the threshold of human visual perception and was therefore not considered relevant. RGP-fed milk also showed increased calcium and potassium concentrations, while RGP_12 milk exhibited the highest phosphorus content. In addition, the lowest RGP levels (RGP_6) reduced the rennet coagulation time while increasing milk curd aggregation rate. Despite these targeted effects, the overall milk composition remained stable, which is critical for maintaining its technological functionality. Full article

The Raramuri Criollo (RC) cattle is recognized for its adaptability, resilience, and low feeding requirements under low-input production systems. This study compared the productive and reproductive performance of purebred RC and Angus × Raramuri Criollo (AC) heifers with Hereford × Angus (HA) heifers. Experiment I evaluated post-weaning growth, feed intake, and feed efficiency in a 56 d individual feeding trial using 10 RC, 10 AC, and 8 HA heifers after a 14 d adaptation period; heifers received the experimental diet ad libitum throughout the trial. Experiment II evaluated puberty attainment and growth development of 14 RC, 17 AC, and 11 HA heifers under rangeland with limited supplementation (RLS) and 11 RC, 16 AC, and 10 HA heifers under annual irrigated pasture (AIP). Puberty attainment was determined from two consecutive serum progesterone concentrations >1 ng/mL, and body weight, average daily gain (ADG), age at puberty (AP), and body weight at puberty (BWP) were analyzed using mixed models and Kaplan–Meier survival analysis. Under individual feeding, RC and AC heifers gained 0.56 ± 0.06 and 0.32 ± 0.06 kg/d less and consumed 40.4% and 22.0% less feed than HA heifers (p < 0.05), whereas feed conversion and residual feed intake did not differ among breed groups. Heifers developed under AIP attained puberty earlier than those under RLS (median AP: 369 vs. 546 d; logrank p < 0.001). Overall, AC heifers combined the adaptive capacity of RC cattle with the productive potential of British breeds, achieving a favorable balance among growth, feed intake, feed efficiency, and reproductive development under contrasting development conditions, supporting their use in low-input beef production systems. Full article

Reliable preimplantation embryo sexing is relevant in cattle breeding; however, PCR-based Y-marker detection may be sensitive to limited DNA input and sample-type-specific properties of embryo-derived material. In this observational study, we examined assay-output patterns in a low-input multiplex PCR workflow targeting a male-specific Y-chromosome marker (MSY) together with an autosomal internal control targeting cyclin-dependent kinase 1 (CDK1). A total of 141 bovine embryo-derived samples were analyzed across three sample categories: whole embryos, cleavage-stage blastomere biopsies, and blastocyst-stage trophectoderm biopsies. Assay evaluability differed across sample categories, being highest in blastocyst-stage biopsy samples (90.6%, 29/32), intermediate in whole embryos (82.9%, 58/70), and lowest in blastomere-biopsy samples (64.1%, 25/39). Among technically evaluable CDK1-positive samples, apparent MSY-positive classification also differed across categories, with rates of 55.2% (32/58) in whole embryos, 52.0% (13/25) in blastomere-biopsy samples, and 6.9% (2/29) in blastocyst-stage biopsy samples. In a same-lysate repeat-amplification subset, overall evaluability concordance was 92.5% and overall apparent MSY-based classification concordance was 88.2%, although subgroup sizes were limited. Because no independent reference method for true embryo sex was available and sample category was structurally confounded with developmental stage, semen type, sire, and partly PCR-date structure, the findings should be interpreted as assay-output observations rather than measures of biological sex ratio or diagnostic sexing accuracy. Overall, embryo-derived sample categories showed differing assay evaluability and apparent MSY-classification patterns within this low-input PCR setting, supporting the need for sample-type-specific validation when low-cell embryo-derived samples are used. Full article

Assessment of the stability of inflammatory parameters in bovine blood samples is important because it enables evaluation of the impact of preanalytical factors on biomarker preservation, standardization of sample processing and storage conditions, as well as reliable and consistent interpretation of results in diagnostic and research studies. The aim of the work was to evaluate the stability of the most common inflammatory markers in the blood of cows in early lactation. The influence of the serum–clot contacts duration and the storage of the separated serum in 24 cows, at 25 °C and 4 °C, in intervals of 0–24 h, was examined. Concentrations of interleukin 1 and 6 (IL-1, IL-6), tumor necrosis factor α (TNF-α), interferon γ (IFN-γ), haptoglobin (Hp), serum amyloid A (SAA) and extracellular heat shock protein 70 (eHsp70) were determined by ELISA method, stability was assessed by ANOVA analysis and maximum permissible instability method. Stability was determined over a range of 2–15 h for IL-1, 8–24 h for IL-6, 9–13 h for TNF-α, 10–20 h for IFN-γ, 20–24 h for Hp, 15–24 h for SAA, and 9–12 h for eHsp70. The stability was strongly dependent on temperature and sample type, with storage at 4 °C providing the highest stability in most cases, while differences between serum and serum–clot samples were analyte-specific and less consistent compared to the effect of temperature. Full article

Rumen methane emissions contribute to global warming and energy loss in cattle. The use of plants rich in secondary metabolites to mitigate methane emissions has been extensively studied, with varying outcomes. The primary aim of this meta-analysis was to assess the impact of secondary metabolites on methane production, productive performance, and ruminal fermentation in beef cattle supplemented with plant-based additives. In accordance with the PRISMA guidelines, 43 of the 578 studies were selected for analysis, employing random-effects models to estimate the raw and standardized mean differences (RStudio: metafor and ggplot, with significance thresholds of p ≤ 0.05 and p ≤ 0.1). Heterogeneity was evaluated using the I² statistic, alongside a subgroup meta-regression examining variables such as dose, additive type, additive form, and forage-to-concentrate ratio. After performing Egger’s test and trim and fill analysis, it was determined that tannins reduced methane yield (g/kg DM, adjusted SDM = −0.463), increased propionate production (%, RMD = 0.066, p = 0.001), rumen pH (adjusted SMD = 0.307), and organic matter intake (RMD = 0.066, p = 0.01). Despite phenolic compounds, flavonoids, terpenes, and terpenoids successfully modulating methane production, fermentative parameters, and nutrient intake, the limited number of comparisons and publication bias suggest caution in generalizing these results. In conclusion, supplementation with plant-based additives containing tannins offers a promising nutritional strategy for reducing enteric methane emissions while maintaining beef cattle performance. Full article

Haemonchus contortus is one of the most prevalent gastrointestinal nematodes in all ecosystems in Mexico, where sheep are raised on pasture, and it poses a significant threat. This study aimed to examine the surgical isolation of a Mexican H. contortus strain, its morphological and molecular characterization, and the maintenance of this strain for future research. Biological behavior and some phenotypic aspects of the adults were considered. Fecal samples were obtained from naturally infected sheep, larval cultures were performed, and a nematode-free lamb was infected. Once the infection was established, the donor sheep were euthanized, the adults recovered, and H. contortus females and males were selected. A surgical transfer from H. contortus adult to the abomasum of a receptor lamb was performed, and the beginning of the egg excretion was confirmed three days post-transfer; fecal cultures from the receptor lamb were conducted to verify the purity of the strain. After three lambs were infected with 3000, 5000, and 10,000 L3, the pre-patent period, prolificacy, and measurements of the adult stages of the strain were studied. The molecular characteristics were evaluated by qPCR; primers were designed based on NCBI genomic DNA sequences of H. contortus to amplify a 176 bp fragment, and the amplicon was sequenced for taxonomic identification. The results of this study describe biological characteristics and some phenotypic aspects of the adults, as well as eggs and infective larvae, and molecular characteristics of the isolated strain, and establish a successful methodology for isolating and maintaining a pure strain of H. contortus (FESC-strain); it can be used as a reference in experimental infections or anthelmintic resistance studies. Full article

Visceral organ mass is a major determinant of maintenance energy requirements in cattle, suggesting that equations to predict visceral organ mass could increase the accuracy of estimates of energy requirements. The objective of this meta-analysis was to quantify the relationships of visceral organ mass with the chemical composition of the diet, as well as animal and management characteristics. A database of 170 treatment means from 38 studies was assembled from published literature. Mixed-effects models with animal, management, and diet characteristics as fixed effects and study as a random effect were selected based on the lowest corrected Akaike information criterion (AICc) and evaluated via leave-one-trial-out cross-validation. Out of 16 organs, 15 had concordance correlation coefficient (CCC) values over 0.900, and cross-validated coefficient of determination (R²) values ranged from 0.728 to 0.967 across organs. Dry-matter intake, days on feed, and fiber-related diet characteristics (roughage level, neutral detergent fiber, and physically effective neutral detergent fiber) were the most consistently retained predictors, with crude protein and metabolizable energy concentrations being retained less frequently. These equations provide a quantitative basis for more accurate estimation of visceral organ mass in cattle. Full article

Cow-based calf rearing (dam- or foster cow-based) is gaining popularity as a relatively natural husbandry practice. However, direct udder contact by calves creates a bidirectional transmission route for pathogens. The objective of this cross-sectional study was to investigate the prevalence and concordance of mastitis-associated pathogens in the milk of cows and the saliva of corresponding calves at the time of weaning. On 15 organic dairy farms, milk samples from 269 cows and saliva samples from 403 calves were collected at weaning. Pathogen differentiation was performed via Matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF), and strain typing was additionally conducted via randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). Dominant pathogens in milk were Non-aureus-Staphylococci (NaS)/Mammaliicoccus spp. and Corynebacterium spp., and in calf saliva, NaS/Mammaliicoccus spp. (primarily M. sciuri, S. xylosus). There were a total of 12 strain concordances, exclusively in foster cow–calf pairs (Fisher’s exact test, p = 0.012). The highest observed/expected ratio was found for P. multocida (21.1). For S. aureus, strain matches were found in 3 foster cow–calf pairs across 2 farms. Direct strain concordance was generally observed rather rarely. The observed strain concordances suggest transmission between cows and calves, particularly for S. aureus and P. multocida. NaS and Mammaliicoccus spp. concordances are likely attributable to a common environmental source. Full article

Bovine-associated microbial communities play important roles in animal physiology, immune regulation, and mammary health. However, knowledge regarding bacterial populations associated with blood and milk remains limited in healthy dairy cattle exposed to different environmental conditions. In this study, we characterized and compared blood- and milk-associated bacterial communities from clinically healthy Holstein cows during summer and winter in an intensive commercial dairy production system located in northern Mexico using 16S rRNA metabarcoding. Significant differences in alpha and beta diversity metrics were observed according to sample type and season. Milk samples exhibited higher microbial richness and diversity than blood samples, and comparative analyses revealed significant differences in bacterial community composition between sample types and seasonal sampling periods. Bacterial communities were mainly dominated by Proteobacteria, Firmicutes, Actinobacteriota, and Bacteroidota. Differential abundance analyses identified genera associated with environmental exposure or opportunistic infections, including Staphylococcus, Streptococcus, Corynebacterium, Pseudomonas, and Acinetobacter. Overall, the observed bacterial community patterns varied according to sample type and seasonal environmental conditions, highlighting the complexity of host-associated microbial ecosystems in dairy cattle. Full article