Responses of dairy cows to treatment with sometribove (r-BST) during three consecutive years

Abstract

Cows were treated with sometribove to study long-term effects. In the first year, 64 cows were randomly assigned to two treatments, placebo (C) or 500 mg sometribove (S), and injected every 14 days for 32 weeks (first 2 years) or for 28 weeks (third year), starting at Week 9 (first 2 years) or Week 13 (last year) post partum. Diets were totally mixed rations (TMR), fed individually and ad libitum, with energy densities targeted to production level. Milk yields, feed intakes and body weights were recorded daily. Milk composition was determined at four consecutive milkings per week. Somatic cell counts in milk (SCC) were recorded regularly. Number of cows in the second year was 20 (C) and 20 (S) and in the third year 14 (C) and 10 (S). The main reasons for removal were: barren cows (6 C, 7 S); unsuitable lactation period particularly after the first year (1 C, 6 S); serious mastitis (0 C, 3 S); teat injury by hooftrapping (0 C, 2 S). Main effects of S during treatment periods for the 14 C and 10 S cows in the first, second and third year, respectively, were: kg 4% FCM, + 19, + 15, −17; NE intake, + 9, + 9, + 6; 4% FCM kVEM −1, + 9, + 7, + 8; body weight, −1, + 5, + 6. There were no significant differences in milk composition between C and S. SCC tended to be higher in S but the difference was not significant. After the first lactation only, sets of twins were higher in S (7) than in C (1). During the pretreatment periods of the second and third year feed intake was higher but feed efficiency was lower in S. The study supports the continual efficacy and safety of sometribove over 3 years of treatment.