Effects of hainanmycin or monensin supplementation on ruminal protein metabolism and populations of proteolytic bacteria in Holstein heifers

Three ruminally cannulated cows were used in a 3 × 3 Latin square design (21-d periods) to evaluate effects of hainanmycin (HAI) or monensin (MON) supplementation on ruminal protein metabolism and populations of proteolytic bacteria in Holstein heifers. The three dietary treatments were: (1) basal diet (control); (2) basal plus 20 mg/heifer per day HAI and (3) basal plus 350 mg/heifer per day MON. The supplementation with HAI and MON had minor effects on ruminal pH and total VFA. In general, HAI and MON decreased acetate, butyrate concentrations, and acetate to propionate ratio, and increased propionate concentration. Supplementation of HAI and Mon resulted in higher relative population sizes of the genus Prevotella and Prevotella ruminicola, and fewer Butyrivibrio fibrisolvens and hyper-ammonia-producing bacteria (P<0.05). HAI supplementation increased concentrations of peptide nitrogen and amino acid nitrogen, and reduced ammonia concentration (P<0.05), and decreased peptidase and deaminase activities (P<0.05). Overall, HAI was as effective as monensin as ionophore in regulation of ruminal protein metabolism and populations of proteolytic bacteria for dairy cows.