The effect of hexoestrol implantation on growth and certain carcass characteristics of fattening steers.

A review of the literature shows that the subcutaneous implantation of stilboestrol increases rate of gain in weight and efficiency of food conversion in lambs (Andrews, Beeson & Harper, 1949; Jordan, 1950; Perry, Andrews & Beeson, 1951; O’Mary, Pope, Wilson, Bray & Casida, 1952; Means, Andrews & Beeson, 1953) and in cattle (Clegg 8t Cole, 1954). The oral administration to fattening steers of stilboestrol, hexoestrol or dienoestrol gives similar results (Culbertson, Burroughs, Kastelic, Hammond & Cheng, 1954; Shanks, 1955; Perry, Beeson, Andrews & Stob, 1955). Hormone treatment, however, reduces carcass quality (Jordan, 1950, 1953 ; O’Mary et al. 1952; Andrews & Beeson, 1953; Clegg & Cole, 1954; Perry et al. 1955). Lower carcass grade in treated animals is due mainly to less fat covering over the carcass. Sometimes the meat may look dark red and slightly coarse and the carcasses appear to be heavy over the shoulder and neck regions and light in the loins. Undesirable side-effects such as elevation of the tail-head and excessive development of mammary tissue may occur. These changes tend to disappear by the end of 90 days after treatment (Clegg & Cole, 1954). Published reports on the composition of the increase in live-weight gain are sparse and sometimes contradictory. There are reports of increased nitrogen retention, probably in the form of protein, in both sheep and cattle (Jordan, 1953; Whitehair, Willis & Bell, 1953; Clegg & Cole, 1954). On the other hand, the weight of muscle in sample cuts from control and treated wether lambs in one experiment showed no significant difference (O’Mary et al. 1952). Greater bone growth has also been reported (Dinusson, Andrews & Beeson, 1950; O’Mary et al. 1952). The subcutaneous fat of treated animals had been shown to contain more water (O’Mary et al. 1952). These results have been obtained only under a rather restricted set of farming conditions. The quality and nature of the roughage portion of the diet has been shown to influence significantly the response to hormone treatment. Steers and heifers on irrigated pasture without supplementary feeding did not increase in weight more than control groups (Clegg & Cole, 1954). In a field trial with 9000 lambs implanted with stilboestrol and fed on maize and poor-quality hay, 2000 died, mainly as a result of prolapse of the uterus and rectum (Jordan, 1953). The object of the present experiment was to determine the effects of hexoestrol implantation on steers given a winter fattening ration consisting of roots, silage, straw and concentrates.