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 for all treatment groups. The increase was largest for the group that was administered 160 mg of bST: milk yield was 34.1 and 53.2% and 6% FCM was 36.9 and 51.8% for parts 1 and 2 of the study, respectively. Sometribove increased milk fat during part 1 of the study, but decreased milk fat during part 2. Protein contents of milk were decreased throughout the study. For all group, bST increased the yield of milk constituents over that of the controls. When milking frequency was reduced from twice to once daily, the difference in milk yield between control ewes and those treated with bST was maintained. Neither mastitis incidence nor milk SCC were affected by bST treatment. Recombinant bST is efficacious in increasing both actual milk yield and 6% FCM over the dose range of 80 to 240 mg/14 d without adverse effects for lactating ewes.