CHANGES IN CARCASS PROPORTIONS AND FAT DEPOSITION IN CONTROL AND HORMONE-TREATED HOLSTEIN-FRIESIAN STEERS

In a study of 72 Holstein-Friesian steers, 1/2 of which were treated with hormones (200 mg of progesterone plus 20 mg of estradiol-17.beta.-benzoate), variation in carcass weight was poorly correlated with lean meat deposition in various sections of the carcass, even though fat deposition during the growth period from 340 to 703 kg liveweight significantly altered carcass proportions. Increasing carcass size from 172 to 393 kg did not significantly change the proportion of chuck but significantly (P < 0.05) decreased the tail, rump, tip, round, butt and shanks and increased the short loin, rib, brisket and flank. These changes can be attributed to different rates of fattening in various sections of the carcass while lean disposition is relatively constant. Hormone treatment improved carcass lean yield by depressing fat deposition.