Effects of bamboo leaf extract on the production performance, rumen fermentation parameters, and rumen bacterial communities of heat-stressed dairy cows

Objective An experiment was conducted to evaluate the effects of bamboo leaf extract on the production performance, rumen fermentation parameters, and rumen bacterial communities of heat-stressed dairy cows. Methods The experiment comprised a 14-day adaptation period and a 21-day experimental period and was conducted in a high-temperature and humidity environment (daily mean ambient temperature = 33.5±1.3℃; daily mean relative humidity = 64.9±0.8%, daily mean temperature-humidity index = 86.2±0.4). Twelve Holstein dairy cows were randomly allocated into two groups. A total mixed ration (TMR) supplemented with bamboo leaf extract at 0 (CON) and 1.3 g/kg dry matter (BLE) were fed, respectively. Feed intake and milk yield were recorded daily. Milk samples were collected on 1, 11 and 21d of the experimental period to analyze milk performance. Rumen fluid samples were collected on 21d of the experimental period to analyze rumen fermentation parameters and rumen bacterial communities. Results Compared with the control group, supplementation of bamboo leaf extract increased milk yield (p<0.01), milk fat yield (p=0.04), 4% fat-corrected milk (p<0.01) and milk fat content (p<0.01); reduced somatic cell count (p<0.01). No differences in dry matter intake and milk protein or lactose content were observed between two groups. Supplementation of bamboo leaf extract also increased the rumen total volatile fatty acid (p<0.01), acetate (p<0.01), butyrate (p<0.01), and valerate (p=0.05) concentrations. However, no significant effects were observed on rumen pH, ammonia nitrogen, propionate, acetate/propionate ratio, isobutyrate, or isovalerate. Furthermore, bamboo leaf extract increased the rumen bacterial abundance and the diversity of the rumen bacterial community. Bamboo leaf extract reduced the Firmicutes/Bacteroidetes abundance ratio and increased the abundances of Butyrivibrio_2 (p<0.01) and Ruminococcus_2 (p<0.01). Conclusion Bamboo leaf extract supplementation at 1.3 g/kg DM could improve production performance and rumen fermentation in dairy cows during heat stress.