EFFECTS OF PROLONGED RELEASE RECOMBINANT PORCINE SOMATOTROPIN AND DIETARY-PROTEIN ON THE GROWTH, FEED-EFFICIENCY, CARCASS YIELD AND MEAT QUALITY OF PIGS

The effects of prolonged release recombinant porcine somatotropin (rpS T) and dietary protein were tested in 108 Lacombe pigs, allocated to c ontrol or rpST treatments at 70 kg and fed isoenergetic diets containi ng one of three protein levels (14, 17 or 20% CP). Recombinant derived porcine somatotropin was implanted in the ear weekly (Monsanto Agricu ltural Co., St. Louis, #CP 115409, 12 mg wk-1). The control animals we re given a weekly sham injection for a minimum of 4 wk. The prolonged release rpST had no effect on average daily gain (ADG, P > 0.05), but did reduce both the feed:gain ratio (F:G, P< 0.07) and dressing percen tage (7 g kg-1 reduction. P < 0.05). Although both the fat thickness ( 10th rib) and kidney fat were reduced 5.6 and 13.9%, respectively, the absolute organ weights for kidneys, liver. lungs and gastrointestinal tract increased between 5 and 10% in prolonged release rpST treated p igs compared with control pigs (P < 0.05). Bone also increased by 6 g kg-1 (P < 0.05) in prolonged release rpST treated pigs. but carcass mu scle or fat proportions were not different. Prolonged release rpST cau sed a higher ultimate muscle pH, moisture content and shear value (P < 0.06) and lower drip loss and expressable juice (P < 0.05) compared w ith meat from control carcasses. Increasing the dietary protein had no effect on ADG, but did improve the F:G ratio (P < 0.05). Carcass dres sing proportion decreased with increasing protein level, but carcass l ean content increased 5 g kg-1 for every 3% increase in crude protein. Simultaneous reductions in carcass fat. marbling and drip loss were o bserved (P < 0.05) as protein level increased. The data suggest that t he current prolonged release rpST (12 mg pellets) shows marginal effec ts on growth and carcass composition. Some nutrient redirecting was ap parent and improvements in the processing value of pork may result.