The present experiment was carried out to analyze the longitudinal changes in milk microorganisms. For this purpose, milk samples were collected from 12 healthy cows (n = 96; six primiparous cows and six multiparous cows) at eight different time points. The characteristics and variations in microbial composition were analyzed by 16S rRNA gene high-throughput sequencing. In the primiparous group, higher and more stable alpha diversity was observed in transitional and mature milk compared with the colostrum, with no significant difference in alpha diversity at each time point in the multiparous group. Proteobacteria, Firmicutes, Bacteroidota, and Actinobacteriota were the most dominant phyla, and Pseudomonas, UCG-005, Acinetobacter, Vibrio, Lactobacillus, Bacteroides, Serratia, Staphylococcus, and Glutamicibacter were the most dominant genera in both primiparous and multiparous cow milk. Some typically gut-associated microbes, such as Bacteroides, UCG-005, and Rikenellaceae_RC9_gut_group, etc., were enriched in the two groups. Biomarker taxa with the day in time (DIM) were identified by a random forest algorithm, with Staphylococcus showing the highest degree of interpretation, and the difference in milk microbiota between the two groups was mainly reflected in 0 d–15 d. Additionally, network analysis suggested that there were bacteria associated with the total protein content in milk. Collectively, our results disclosed the longitudinal changes in the milk microbiota of primiparous and multiparous cows, providing further evidence in dairy microbiology.

Objective: The objective of this study was to evaluate the growth performance, rumen fermentation parameters and bacterial community of post-weaning dairy calves in response to five diets varying in corn silage (CS) inclusion.Methods: A total of forty Holstein weaned bull calves (80±3 days of age;128.2±5.03 kg at study initiation) were randomized into five groups (8 calves/group) with each receiving one of five dietary treatments offered as total mixed ration in a 123-d feeding study. Dietary treatments were control diet (CON; 0% CS dry matter [DM]); Treatment 1 (T1; 27.2% CS DM); Treatment 2 (T2; 46.5% CS DM); Treatment 3 (T3; 54.8% CS DM); and Treatment 4 (T4; 67.2% CS DM) with all diets balanced for similar protein and energy concentration.Results: Results showed that calves offered CS had greater average daily gain, body length and chest depth growth, meanwhile altered rumen fermentation indicated by decreased rumen acetate concentrations. Principal coordinate analysis showed the rumen bacterial community structure was affected by varying CS inclusion diets. Bacteroidetes and Firmicutes were the predominant bacterial phyla in the calf rumens across all treatments. At the genus level, the abundance of Bacteroidales_RF16_group was increased, whereas Unclassified_ Lachnospiraceae was decreased for calves fed CS. Furthermore, Spearman’s correlation test between the rumen bacteria and rumen fermentation parameters indicated that Bacteroidales_RF16_group and Unclassified Lachnospiraceae were positively correlated with propionate and acetate, respectively.Conclusion: The results of the current study suggested that diet CS inclusion was beneficial for post-weaning dairy calf growth, with 27.2% to 46.5% CS of diet DM recommended to achieve improved growth performance. Bacteroidales_RF16_group and Unclassified Lachnospiraceae play an important role in the rumen fermentation pattern for post-weaning calves fed CS.

The present experiment was carried out to assess the effects of reconstituted milk (RM), acidified reconstituted milk (ARM), and acidified fresh milk (AFM) on growth performance, diarrhea rate, and hematological parameters of preweaning dairy calves. For this purpose, a total of 27 Holstein female calves (one month of age) with initial body weight of (67.46 ± 4.08) kg were divided into three groups in such a way that each group contained nine calves. Calves were housed individually, and starter was offered ad libitum to each calf. The dietary treatments were RM, ARM, and AFM. The highest milk intake was observed in calves receiving AFM as compared to other treatments (p < 0.01). Calves fed AFM had more feed intake than those fed ARM and RM (p < 0.01). Feed efficiency was significantly lower for calves offered ARM than those offered RM and AFM (p < 0.01). A lower withers height growth was found for calves fed RM than those fed ARM and AFM (p <0.05). Diarrhea rate and white blood cell (WBC) and lymphocytes (LYM) counts were greater for calves fed RM than those fed ARM and AFM (p < 0.05). These findings suggested that ARM and AFM had positive effects on growth performance and health status of the preweaning dairy calves.

This study aimed to scientifically assess cold stress in dairy calves and optimize winter rearing protocols. A combined approach of feeding trials, expert surveys, and multidimensional data analysis was used to evaluate the effects of outdoor (−5~−28 °C) and indoor (5 °C) environments on Holstein dairy calves. A 60-day controlled trial was conducted with 20 healthy 5-day-old calves. In parallel, an interdisciplinary panel of 20 experts and 8 farmers established a cold stress evaluation system via the analytic hierarchy process (AHP), with cold stress levels quantified through fuzzy comprehensive evaluation. Environmental (weight = 0.62), physiological (weight = 0.22), and behavioral (weight = 0.16) factors contributed differentially to cold stress assessment, with data showing that outdoor calves were under mild cold stress (maximum membership degree = 0.64). The temperature–humidity index (THI) showed significant correlations with multiple physiological and biochemical parameters. Generalized linear mixed model (GLMM) analysis confirmed that THI variation significantly influenced calf standing time, respiratory rate (RR), malondialdehyde (MDA) content, and total antioxidant capacity (T-AOC). In feeding trials, indoor calves exhibited marginally higher average daily gain and body weight in early stages, whereas outdoor calves demonstrated significantly better growth performance by day 60. The outdoor group displayed increased lying and defecation behaviors, along with reduced locomotor/standing time and respiratory frequency. No significant intergroup differences were observed in serum immune or antioxidant indicators. Metabolomic analysis identified 20 differentially expressed metabolites, indicating an enhancement in the activity of energy metabolism pathways in calves. This study establishes a quantitative methodology for cold stress evaluation, clarifies environment–physiology–behavior interactions, and provides a theoretical basis for winter calf management. The results confirm that outdoor cold exposure did not hinder calf growth without compromising health, offering scientific support for optimizing outdoor rearing strategies in cold regions.