Effect of Sometribove on Rumen Fermentation, Rate of Passage, Digestibility, and Milk Production Responses in Dairy Cows

¹ Department of Animal Science, Utah State University, Logan 84322-4815

Six ruminally and duodenally fistulated Holstein cows 60 d postpartum were assigned randomly to each of two treatments in a single reversal design. Treatments consisted of placebo or 25 mg of sometribove (bST) injected daily. Treatments were initiated at 60 d ± 7 postpartum and maintained for 6 wk with a 3-wk adjustment between treatment periods. All cows received a TMR consisting of 16% CP and 1.67 Mcal of NE_L/kg of DM. Influence of bST on rumen fermentation characteristics, digesta rate of passage, apparent nutrient digestibility, and milk production was evaluated.

Milk yield of treated animals was 4.0 kg/d higher than controls. The 3.5% FCM and milk production efficiency (3.5% FCM/DMI) were significantly higher in treated animals than in controls (29.0 vs. 25.4 kg/d and 1.38 vs. 1.21 kg/ kg, respectively).

Percentage of rumen cellulolytic bacteria (of total viable bacteria) was not significantly different for bST-treated animals (6.4 vs. 3.4%). Total number of rumen protozoa tended to be higher (7.25 vs. 6.55 x 10³/ml) in bST-treated animals.

Ruminal percentages of CP, NH₃ N, -amino N, VFA, and pH were unaffected by treatment. Sometribove treatment did not significantly affect liquid dilution or solids turnover rates. Percentages of CP, -amino N, and NH₃ N content in duodenal samples were unaffected by treatment. Total tract apparent digestibility of nutrients and mean daily DMI were unaffected by treatment.

Key Words: sometribove • milk yield • ruminal parameters

Submitted on March 25, 1991
Accepted on May 31, 1991