Farmers are receiving a price incentive to produce more milk during the summer months. Bovine somatotropin (BST) could be used as a means of increasing milk yield from late winter/spring calving cows during the summer months. However, most of the research work with BST has been with housed cattle on winter feeding systems. The objective of this experiment was to evaluate the use of BST with grazing cattle supplemented with silage as a buffer feed.

Thirty-six January to March calving multiparous Friesian dairy cows were allocated to 4 treatments: CG - Control/Grazing, TG - Treated/Grazing, CB - Control/Buffer fed, TB - Treated/Buffer fed. The treated cattle were given 640 mg of recombinantly derived bovine somatotropin (Somidobove Elanco Products Limited) in a sustained release formulation at 28 day intervals. The treatment period at grass lasted for 8 weeks from 18 August 1988. The cattle were then housed for a further 8 weeks in 2 groups of sixteen cows (with one block of cows omitted from the experiment).