INTERRELATIONSHIPS BETWEEN SEX AND RACTOPAMINE ON PROTEIN AND LIPID DEPOSITION IN RAPIDLY GROWING PIGS

Sixty pigs were used to investigate the effects of two levels of dieta ry ractopamine (RAC; 0 and 20 mg/kg) and three sex types (SEX; boars, gilts, and barrows) on performance over the live weight range 60 to 90 kg. Pigs were housed in individual pens and allowed ad libitum access to a diet containing 3.466 Mcal of DE and 10.7 g of lysine/kg. Contro l boars exhibited faster and more efficient growth and deposited more protein and less fat than gilts or barrows. The RAC increased ADG by 1 7 and 21% in gilts and barrows but not in boars. Feed intake was not a ltered by dietary RAC. Dietary RAC increased the rate of protein depos ition by 15, 42, and 41% in boars, gilts, and barrows, respectively. N evertheless, the daily rate of protein deposition was greatest in RAC- treated boars. The RAC tended to reduce the daily rate of fat depositi on by 21% in boars but not in gilts or barrows. Carcass protein conten t increased by 5% and fat content decreased by 8% in response to RAC. These improvements in carcass composition occurred without compromisin g meat quality. Results show that RAC is a potent stimulator of protei n deposition in finishing pigs. However, increased protein deposition is not necessarily at the expense of fat deposition.