Effects of root extracts of three traditional Chinese herbs as dietary supplements on dry matter intake, average daily gain, rumen fermentation and ruminal microbiota in early weaned yak calves

Herbal supplements are being tested as alternatives to antibiotics in enhancing the performance of livestock. The present study evaluated the effects of herbal root extracts from three traditional Chinese medicinal herbs as dietary supplements on dry matter intake (DMI), average daily gain (ADG), rumen fermentation and ruminal microbiota in early weaned yak calves (Poephagus grunniens). Twenty, four-month old weaned yak calves (72.3 ± 3.65 kg) were divided into four groups, matched for bodyweight and sex (n = 5 per group), and received either no supplement (control group) or 80 mL/kg DMI of herbal root extracts of Angelica sinensis, Codonopsis pilosula or Glycyrrhiza uralensis. The water extract (∼170 mL) was mixed with 300 g concentrate and offered to the calves each day for 60 days following a 14-day adaptation period. Dry matter intake did not differ among treatments, but ADG was highest for calves fed Codonopsis pilosula root extract (P = 0.026). Compared with control calves, calves fed root extract of Glycyrrhiza uralensis had a higher ruminal proportion of propionate (P = 0.034), calves fed root extracts of Codonopsis pilosula and Glycyrrhiza uralensis had higher ruminal proportions of isovalerate (P = 0.032) and calves fed root extract of Glycyrrhiza uralensis had a lower acetate:propionate ratio (P = 0.027) on d 30. Calves consuming Angelica sinensis, Codonopsis pilosula and Glycyrrhiza uralensis root extract had lower ruminal NH₃-N concentrations than control calves on d 60 (P < 0.05). The abundances of Bacteroidetes and Firmicutes comprised over 90 % of the total phyla in the four groups. Yak calves consuming Glycyrrhiza uralensis root extract had the highest abundance of Bacteroidetes (P = 0.009) and lowest abundance of Firmicutes (P = 0.023). Calves consuming Codonopsis pilosula root extract had the highest abundances of Proteobacteria (P = 0.035) and Actinobacteria (P = 0.007), while calves consuming the three herbal root extracts tended to have lower abundances of Kiritimatiellaeota (P = 0.082), Spirochaetes (P = 0.081) and Synergistetes (P = 0.058) than control calves. In conclusion, consuming Codonopsis pilosula root extract increased ADG in early weaned yak calves, while consuming the three herbal root extracts increased ruminal proportions of propionate and isovalerate, and altered rumen microbiota. Supplementary Codonopsis pilosula proved to be the most beneficial of the three herbal roots for the early weaned calves.