Hexoestrol implantation of steers fattened at pasture I. Effects on growth and herbage intake

Abstract

The possibility of using hormones to increase the productivity of meat animals has been considered for a number of years (Hammond, 1957 and Scarisbrick, 1960). Lamming (1957) has pointed out that most of the work with hormones and beef cattle has been done in the U.S.A. under feedlot conditions. In this country Aitken and Crichton (1956), Dodsworth (1957) and Lamming (1957 and 1958) all obtained increases in rates of gain with implantation. Lamming found that responses in steers varied from 0 to 15% increase in gain per day in spring, about 20% in summer, 40% in autumn, i n each case on pasture and up to 60% under winter feeding conditions. He also used several levels of implantation, from which it appeared that the optimum level was about 45 mg. hexoestrol. Smith (1958) described trials conducted at eight farms in the North of Scotland in which 189 steers fattened solely on grass were implanted with hexoestrol. Implantation resulted in an extra daily live-weight gain of about 0·5 lb. Increases in dose levels above 60 mg. produced no significant response in terms of live-weight gain. Eighteen experiments at Experimental Husbandry Farms and the Norfolk Agricultural Station, described by Jones (1961), also showed that live-weight gain was increased by implanting; that the correct dose to give maximum response appeared to be 45 to 60 mg. hexoestrol; and that the implant should be made from 100 to 130 days before slaughter. Second implantations were made in several of these experiments and it appeared doubtful if this practice was desirable. In New Zealand, Lucas (1958) and Everitt (1959) also found that hexoestrol implantation increased weight gains of grazing steers.