Heat stress negatively affects lactation performance and rumen microbiota of dairy cows, with different breeds showing varying levels of heat tolerance. This study aimed to compare the lactation performance of Montbéliarde × Holstein (MH, n = 13) and Holstein (H, n = 13) cows under heat stress, and 16S rRNA sequencing and liquid chromatography–mass spectrometry (LC-MS) were used to determine the rumen microbiome and metabolome in experimental cows. The results indicated that during heat stress, milk yield (p = 0.101), milk fat yield, milk protein yield, milk protein, and milk lactose (p < 0.05) in Montbéliarde × Holstein cows were higher than those in Holstein cows, whereas milk yield variation and somatic cell counts (p < 0.05) were lower than those in Holstein cows. The sequencing results indicated that the rumen of Montbéliarde × Holstein cows was significantly enriched with beneficial bacteria, such as Rikenellaceae, Allobaculum, and YRC22 (p < 0.05). In addition, correlations were observed between specific ruminal bacteria and lactation performance. Ruminal metabolites related to antioxidant and anti-inflammatory properties were significantly higher (p < 0.05) in Montbéliarde × Holstein cows than in Holstein cows. Overall, Montbéliarde × Holstein cows showed higher production efficiency under heat stress, which may be related to the different rumen mechanisms of crossbred and Holstein cows in adapting to heat stress.

Holstein cattle are the main breed of dairy cattle in China. However, given the high degree of purebred selection of Holstein cattle, Chinese dairy cattle are increasingly being characterized by poor disease resistance, poor quality, and declining fertility. In this study, using Montbéliard × Holstein cattle as females and Montbéliard bulls as males for backcross breeding, we sought to provide a reference for improving the quality and performance of Holstein cattle and enhancing the efficiency of dairy farming. On the basis of similar physiological status and age, we selected 24 Montbéliard and Holstein backcross heifers and 11 Holstein heifers fed the same formula for comparative analyses. Plasma samples collected for plasma biochemical index analyses revealed that the content of ALB and BUN in the Montbéliard and Holstein backcross heifers was 20.83% (31.62 g/L to 26.17 g/L) and 42.36% (6.89 mmol/L to 4.84 mmol/L) higher than in the Holsteins (p < 0.01). The ALB/GLB (0.90 to 0.60, p < 0.05) was significantly higher in Montbéliard and Holstein backcross heifers than in Holstein heifers. Similarly, the activity of CAT in the backcross heifers was 61.28% (4.29 U/mL to 2.66 U/mL) higher than that in the Holstein heifers (p < 0.05). Although the activity of GSH-Px in the backcross heifers also showed an increasing trend, the difference did not reach the level of statistical significance (p = 0.052). Compared with Holstein heifers, the concentrations of IgA, IgG, and IL-4 were elevated by 32.52% (24.90 μg/mL to 18.79 μg/mL, p < 0.01), 13.46% (234.32 μg/mL to 206.53 μg/mL, p < 0.01), and 14.59% (306.27 pg/mL to 267.28 pg/mL, p < 0.05), and the contents of IL-6 and TNF-α were decreased by 15.92% (215.71 pg/mL to 256.55 pg/mL, p < 0.01) and 32.17% (7.17 ng/mL to 10.57 ng/mL, p < 0.01) in the plasma of Montbéliard and Holstein backcross heifers. Among the experimental heifers, five animals from each of the two groups were selected for plasma metabolomic analysis based on untargeted liquid chromatography–mass spectrometry. A comparison of the differential metabolites between the two heifer breeds revealed an up-regulation of d-glucuronic acid, s-glutathionyl-l-cysteine, and oleic acid levels in the backcross cattle compared with those in the Holstein heifers. We speculate that changes in the levels of these metabolites may be associated with an enhancement of the anti-inflammatory, antioxidant, and immune systems in these backcross heifers. Collectively, our findings in this study indicate that compared with 12-month-old purebred Holstein heifers, Montbéliard and Holstein backcross heifers of the same age are characterized by higher antioxidant capacity and immunity.

In this study, we investigated the effects of dietary supplementation with thermally modified attapulgite on the daily weight gain, serum biochemical indices, and serum metabolites of Simmental fattening cattle. A total of 30 healthy Simmental fattening beef calves of similar age (8 to 9 months old) and body weight (370 ± 10 kg) were randomly divided into two groups, each containing 15 animals. A control group was fed the basal diet, and a treatment group was fed the same basal diet with the addition of 4 g/kg of thermally modified attapulgite. After 75 days of formal experiment, the calves in the two groups were weighed, and blood samples were collected by tail vein blood sampling for determinations of the serum biochemical indices and serum metabolites using liquid chromatography–mass spectrometry (LC-MS) analysis. The results indicated that the addition of thermally modified attapulgite to the diet had no significant effects on the daily weight gain of fattening beef cattle. After feeding with modified attapulgite, the glutathione peroxidase and superoxide dismutase activities in the serum of the experimental group were 55.02% (257.26 U·mL⁻¹ to 165.95 U·mL⁻¹, p < 0.05) and 13.11% (18.98 U·mL⁻¹ to 16.78 U·mL⁻¹, p < 0.05) higher than that in the control group. Compared with the control group, the tumor necrosis factor-alpha content was reduced by 14.50% (31.27 pg·mL⁻¹ to 36.57 pg·mL⁻¹, p < 0.01), and the concentration of interleukin-6 and lipopolysaccharide decreased by 17.00% (34.33 pg·mL⁻¹ to 41.36 pg·mL⁻¹, p < 0.001) and 23.05% (51.34 EU·L⁻¹ to 66.72 EU·L⁻¹, p < 0.001) in the serum of the experimental group. Contrastingly, the thermally modified attapulgite had no significant effects on the levels of serum total protein, albumin, or globulin in Simmental fattening cattle (p > 0.05). Furthermore, the results of serum metabolomic analyses revealed that there were a total of 98 differential metabolites, which were mainly enriched with respect to glycerophospholipid metabolism, Th1 and Th2 cell differentiation, autophagy-other, retrograde endogenous cannabinoid signaling, and the NF-κB signaling pathway. Overall, thermally modified attapulgite was found to effectively increase the activity of antioxidant enzymes, reduce serum inflammatory mediators, may suppress oxidative damage, enhance immunity, and have a positive influence on the health of Simmental fattening beef calves.

Nitrogen use efficiency (NUE) is commonly calculated as the ratio of milk nitrogen output to nitrogen intake in dairy cows. However, because milk nitrogen output is intrinsically determined by milk production and nitrogen intake is largely driven by dry matter intake, conventional NUE is mathematically dependent on production level and feed intake. This dependency makes it difficult to distinguish apparent efficiency caused by higher milk yield from intrinsic biological efficiency in nitrogen utilization. Therefore, this study aimed to evaluate NUE in dairy cows using a combined mathematical and metabolic framework based on residual NUE (rNUE) analysis. A total of 126 early-lactation Chinese Holstein cows were screened, and 16 high-NUE and 16 low-NUE cows were selected after matching for parity, days in milk, and dry matter intake. High-NUE cows had greater milk yield, milk nitrogen output, and NUE than low-NUE cows, despite similar nitrogen intake. They also exhibited higher ruminal microbial crude protein and ammonia nitrogen concentrations, a lower acetate-to-propionate ratio, and reduced circulating essential and total amino acid concentrations. Multiple regression analysis showed that energy-corrected milk and dry matter intake explained 71.4% of the variation in NUE. The residuals from this model were defined as rNUE, which was independent of milk production. After removing production-related effects, rNUE remained positively associated with ruminal microbial crude protein and ammonia nitrogen concentrations, and negatively associated with the acetate-to-propionate ratio and circulating amino acid pools. These findings indicate that conventional NUE in dairy cows is largely driven by production level, whereas residual-based modeling can identify a production-independent component associated with rumen nitrogen metabolism and amino acid utilization. The residual NUE approach provides a useful mathematical and metabolic framework for evaluating intrinsic NUE in dairy cows beyond milk production level.