Fermented Chinese herbal preparation: Impacts on milk production, nutrient digestibility, blood biochemistry, and antioxidant capacity of late-lactation cows under heat stress

The objective of this study was to investigate the effects of dietary supplementation of fermented Chinese herbal preparation (CHP) on the milking performance, nutrient digestibility, blood biochemistry, and antioxidant capacity in cows under heat stress (HS). A total of 40 late-lactation Holstein cows (Average body weight: 560 ± 51.0 kg, milk per day: 16 ± 3.0 kg) were randomly assigned to 4 groups (10 cows per group). The cows in treatment groups were supplied with 25, 50, or 100 g CHP in diet per cow per day, and the control group was no supplied with CHP. All cows were raised at a natural HS environment (Average THI: 74.5) during 42-d experimental period. Milk, fecal samples, and blood samples were collected on 14, 28, and 42 d for measuring milk production, nutrient apparent digestibility, and serum biochemical parameters, heat shock protein involving HSP70, HSP90, and HSF. The antioxidant enzymes (T-AOC, SOD, CAT, GPx, and PRDX₂) activities in blood and its genes expression level were also measured on 14, 28, and 42 d of experiment. The results showed that the dietary supplementation of CHP demonstrated an increased tendency in DMI (P = 0.08), and 50 or 100 g/d CHP increased milk yield, milk composition (fat and protein) content (all P < 0.05) for the entire 42-d period, compared with the control group. However, there was no difference (P > 0.05) on nutrient digestibility among all groups. From blood biochemistry, the HSP90 or HSP70 level in serum exhibited a decrease (P < 0.05) with CHP supplements. Also, the serum triiodothyronine and glucose content were increased (P ≤ 0.02) by CHP, while the prolactin content demonstrated an increasing trend (P = 0.08). For antioxidant capacity, the doses of CHP increased serum T-AOC (P < 0.05), SOD (P = 0.02), and CAT (P < 0.01) concentration, and the mRNA levels of both SOD and CAT genes were also up-regulated (P ≤ 0.05) for groups with CHP. Besides, there was a positively correlated between milking yield or milk quality (milk protein and milk fat) with DMI (P < 0.01), various of antioxidant enzymes concentrations in serum, or mRNA levels of SOD and CAT (P < 0.05). However, the negative correlation between milking performance and HSP70 or HSP90 was also exhibited (P < 0.05). Therefore, the CHP supplements may improve blood biochemistry and antioxidant capacity under HS to increase milking performance in dairy cows.