Effects of Radix Bupleuri extract supplementation on lactation performance and rumen fermentation in heat-stressed lactating Holstein cows

Radix Bupleuri extract (RBE) has been shown to mitigate negative effects of high ambient temperature. This experiment was conducted to investigate effects of RBE supplementation on lactation performance and rumen fermentation in Holstein cows under heat stress. Forty Holstein cows (75 ± 15 d in milk, 37.5 ± 1.8 kg of milk/d, and 1.7 ± 0.4 parity) were randomly assigned to one of four groups (n = 10). One of four treatment diets, assigned randomly to one of four groups, consisted of RBE supplementation at 0, 0.25, 0.5 or 1.0 g/kg of the basal diet (concentrate and roughage) based on dry matter (DM). Cows were housed in a tie-stall barn and were individually fed the treatment diets. The experiment lasted for 10 wk in hot summer. During the experiment, average ambient temperatures and temperature-humidity indexes (THI) were respectively 27.5 ± 1.5, 29.8 ± 1.9 and 28.1 ± 1.7 °C, and 78.2 ± 2.7, 79.8 ± 3.3 and 78.3 ± 3.4 at 0600, 1400 and 2200 h. Average respiration rates (RR) with RBE at 0.25, 0.50 and 1.0 g/kg were 65.6, 60.3 and 67.4, respectively, vs. 71.4 (breaths/min) for the control (P < 0.01). Average rectal temperatures (RT) were 39.1, 39.0 and 39.1 vs. 39.3 °C for the control (P < 0.01). Moreover, cows supplemented with RBE increased dry matter intake (DMI, 22.8, 21.6 and 22.1 vs. 20.9 kg/d) (P < 0.05) and milk production (34.2, 33.4 and 32.4 vs. 31.6 kg/d) (P < 0.01) compared with control. Percentages of milk protein and fat were similar among groups, while milk protein yield increased with increasing level of RBE (0.97, 0.95 and 0.92 vs. 0.89 kg/d for the control) (P < 0.01). Milk fat yield also increased with RBE (1.13, 1.12 and 1.09 vs. 1.02 kg/d for the control) (P < 0.05). There was no treatment effect on diet apparent digestibility or volatile fatty acid (VFA) concentration among groups. Overall, supplemental RBE at 0.25 or 0.5 g/kg could mitigate the negative effects of heat stress on production in lactating Holstein cows.