Daily injections of bovine pituitary somatotropin (growth hormone) can markedly increase growth and muscle deposition in fattening lambs, although the optimal dose range for these effects is not known.

This experiment was designed to assess the anabolic and lipolytic activities of biosynthetic somatotropin (produced by genetically-modified bacteria) in fattening lambs, and to determine the effects of dose and method of administration.

Dorset Down x Finn-Dorset lambs were individually penned, fed a barley/soyabean meal diet ad libitum (C.P.=155g/kg DM) and allocated to one of six treatment groups, each containing 5 ewe and 5 wether lambs, such that each group had the same initial mean live weight (18 kg). Between 10 and 21 weeks of age, the lambs of each group received one of the treatments shown in Table 1, comparing 3 doses of somatotropin (0.025, 0.1 or 0.25 mg/kg live weight), dissolved in bicarbonate buffer and injected subcutaneously once each day, with the intermediate dose (0.1 mq/kg/day) given by continuous subcutaneous infusion or by daily subcutaneous injection as a suspension in olive oil.