The use of the hormones, diethylstilboestrol, hexoestrol and testosterone propionate, as growth stimulants in beef cattle has been studied.The subcutaneous implantation of 60 mg. stilboestrol into steers fattening in yards produced a highly significant increase in rate of gain (65%) and little difference in the yield and quality of the carcass. The implantation of 24 nig. or 36 mg. of diethylstilboestrol or 30 mg. hexoestrol into Friesian bullocks fattening on pasture produced highly significant increases in rates of gain (29%, 48% and 33% respectively). No significant difference was found in the rates of gain produced by these three treatments.The oral administration of 10 mg. diethylstilboestrol per head per day for 168 days or the oral administration of 20 mg. rising to 40 mg. testosterone propionate per head per day for 154 days to dizygotic twin steers on equal feed intake significantly increased rate of gain by 15% and 21% respectively Feed efficiency as measured by the pounds of feed required to produce a pound of gain was significantly improved by both treatments. Carcass yield and carcass quality were not significantly affected by either treatment. No significant differences were found between the two treatments.Examination of the thyroid and adrenal glands of treated and untreated steers revealed no consistent changes in size due to treatment. The gonadotrophin and thyrotrophin content of the anterior pituitary glands of treated and untreated cattle were compared using the male chick bioassay. The results showed that a lower gonadotrophin content was not a factor associated with the extra growth due to treatment, but in two out of three experiments there was some evidence that sex-hormone treatment leads to a mild hyper-thyroidism which, in turn, resulted in a decrease in the thyrotrophin content of the anterior pituitary gland. It was concluded that hyperactivity of the thyroid gland was probably more important in accounting for the extra growth than hyperactivity of the adrenal cortex.

small crossbreds compared to large crossbreds, but there were no corresponding differences between bulls and steers. At the same proportion of dissected carcass subcutaneous fat, carcasses from large crossbreds and all bulls had greater proportions of muscle, less bone and similar proportions of total fat than small crossbreds and all steers. There were generally no differences for gender and size in the distribution of muscle within each of the wholesale cuts except in the case of the chuck, where bull carcasses had a greater proportion of muscle compared to those from steers. Bone distribution, however, did vary significantly across several wholesale cuts with carcasses from large animals and bulls having lower proportions of bone than those from small animals and steers. Feed conversion rate (g muscle/kg DM) was superior for bulls compared to steers (63 and 56 g muscle/kg DM, respectively), but similar for large and small animals (60 and 59 g muscle/kg DM, respectively). The present data suggest that the evaluation of beef cattle for feed efficiency on a liveweight and muscle basis may yield different conclusions. There were no significant size x castration interactions for any of the growth, efficiency and carcass variables examined.

. 1984. The growth performance and carcass composition of ram and ewe lambs fed on pasture or in confinement and slaughtered at similar fatness. Can. J. Anim. Sci. 64: 631_640.Forty-nine crossbred ram lambs and 62 crossbred ewe lambs were allotted at weaning (average weight 30.6 kg) to pasture (P) or concentrate (C) feeding. The number of lambs per treatment was as follows '. rams, 24 P fed and 25 C fed; ewes, 3 I P fed and 3l C fed. The lambs were slaughtered after 56, 72, 100 andl2l days on feed.Offal components were weighed, and the alimentary tract was emptied of digesta.One side ofeach carcass was broken into four cuts (leg, loin, rib, shoulder) which were further separated into fat, muscle and bone. C-fed lambs were 4.\Vo heavier live than P-fed lambs (P<0.05) and ram lambs were 9.0Voheavier live than ewe lambs (P<0.05) when evaluated at a constant depth of subcutaneous fat (4.5 mm).However, P-fed lambs required an extra 2l days (P<0.05) to reach the same fat depth as C-fed lambs. C-fed lambs had greater rib eye areas than P-fed lambs, but carcasses from all treatments had similar proportions of dissected muscle, bone and fat when evaluated at a constant proportion of subcutaneous fat. P-fed lambs had a greater proportion of their empty bodies as head and reticulo-rumen, and a lower proportion as liver and large intestine than C-fed lambs. Ram lambs had a greater proportion of their empty bodies as head, and a lower proportion as caul fat, mesenteric fat, omasum and small intestine than ewe lambs. Distribution of muscle and bone among each of the four meat cuts which were evaluated was similar for all carcasses. Sex and feeding system had only a minor effect on the distribution of the fat depots. In this study, lambs fed on pasture required 21 days longer on feed to reach the same external fatness as concentrate-fed lambs, but produced carcasses of similar composition at slightly lighter iiveweights (45.3

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