BOVINE SOMATOTROPIN DOSE TITRATION IN LACTATING DAIRY EWES .1. MILK-YIELD AND MILK-COMPOSITION

Seventy-four lactating dairy ewes were injected with recombinant bST ( sometribove) in a sustained-release formulation. Ewes received 0, 80, 160, or 240 mg of bST every 14 d from wk 3 to 8 of lactation (part 1) and 0, 80, or 160 mg of bST every 14 d from wk 11 to 23 of lactation ( part 2). Sometribove increased milk yield over that of the controls fo r sill treatment groups. The increase was largest for the group that w as administered 160 mg of bST: milk yield was 34.1 and 53.2% and 6% FC M was 36.9 and 51.8% for parts 1 and 2 of the study, respectively. Som etribove increased milk fat during part 1 of the study, but decreased milk fat during part 2. Protein contents of milk were decreased throug hout the study. For all groups, bST increased the yield of milk consti tuents over that of the controls. When milking frequency was reduced f rom twice to once daily, the difference in milk yield between control ewes and those treated with bST was maintained. Neither mastitis incid ence nor milk SCC were affected by bST treatment. Recombinant bST is e fficacious in increasing both actual milk yield and 6% FCM over the do se range of 80 to 240 mg/14 d without adverse effects for lactating ew es.