Effects of oestradiol implants on musculo-skeletal growth of wether and ewe lambs

Oestrogenic growth promotants stimulate lean carcass growth and reduce carcass fat in livestock but little is known about their actions on musculo-skeletal growth per se. To investigate such effects, selected bones and muscles were measured in castrated male and entire ewe lambs treated from 4 weeks of age with implants containing oestradiol-17β. Half of the animals were slaughtered at 14 weeks and half at 23 weeks of age. Oestradiol treatment significantly stimulated the linear growth of vertebrae, with the effect being most pronounced in ewe lambs slaughtered at 14 weeks. The treatment also increased the diameter of some limb bones and slightly increased the length and girth of attached muscles. Castrated male lambs tended to have longer bones and longer and heavier muscles than entire ewes. This study showed that, in sheep, oestrogens cause a short-term increase in length in growing bones.