Twenty-eight Border Leicester ♂ × Scottish Blackface ♀ wether lambs aged 47 days and weighing 17 kg on average were allocated to be sham-implanted controls (group C) or implanted with trenbolone acetate (TBA) combined with oestradiol-17β (OE) as follows: 17·5 mg TBA + 2·5 mg OE (group TO1); 35 mg TBA + 5 mg OE (TO2); 52·5 mg TBA + 7·5 mg OE (TO3). The lambs were offered ad libitum a diet containing (per kg dry matter) an estimated 12·5 MJ metabolizable energy and 0·16 kg crude protein. They were slaughtered 60 days following implantation.
On average hormonal treatment resulted in significant increases in (a) live-weight gain, food intake and gut fill, (b) proportions of perinephric and retroperitoneal fat in empty body, (c) carcass lean proportion, and (d) proportion of lean in shoulder and rib joints. Variable changes in the weights of m. semitendinosus, m. gastrocnemius and m. supraspinatus were recorded.
Hormonal treatment, on average resulted in significant reductions in (a) killing-out proportion, (b) proportions of total fat and subcutaneous fat in carcass and (c) proportions of fat in the shoulder, rib and hind leg joints. Treated lambs had smaller thymus glands but larger accessory vesicular glands. Penile tissue was also increased in treated lambs. The proportional differences in live-weight gain and carcass fat content were 0·15 and 0·12 respectively.
Differences in dose level had little effect on growth and carcass characteristics.