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.
The generally accepted view is that, in sheep and cattle, plane of nutrition (as indicated by growth rate) can influence body composition; the higher the rate of gain the greater the fatness at a particular live or carcass weight. However, exceptions to this view can be found which demonstrate that the effective protein: energy ratio of the diet can exert a considerable influence on the composition of live weight gain. Unfortunately most studies which have considered the effects of growth rate on composition (either directly or as a consequence of some treatment which resulted in different growth rates) have described their animals in terms of chemically determined protein, fat, ash and water. To assess the potential economic impact of different growth rates on body composition and the distribution of fat throughout the body requires dissection data, describing the animal in terms of lean, bone and individual fat depots. In this experiment the dissected composition of 44 Hampshire Down x Mule ewe lambs was determined in animals which had followed planned growth paths involving periods of high (H) and low (L) growth.
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