The finishing of store Blackface lambs off grass is often relatively unprofitable due to low growth rates and relies heavily upon changes in seasonal price. Anabolic growth promoters offer means of increasing growth rates and thereby make a relatively large impact on profitability.

Sixty Blackface wether lambs were grazed in each of two years on grass from September until slaughter before March. Whole barley supplementation was commenced in December. Lambs were sold deadweight arid MLC carcase classified. Lambs were sold when judged to be at a standard fat cover.

Lambs were left unimplanted (U), implanted with 12 mg of Zeranol (Z) or with 15 mg of Oestradiol - 17β (O) in September.