DIFFERENTIATION OF THE EFFECTS OF SOMATOTROPIN AND ENHANCED GROWTH-RATE ON THE OCCURRENCE OF OSTEOCHONDROSIS IN PIGS

One hundred and twenty Yorkshire pigs, equal numbers of gilts and barr ows, with an initial average weight of 69 kg were used in the present experiment. The animals were treated with 2 mg d-1 of recombinant porc ine somatotropin (rpST) either by daily injection or by slow-release i mplant, while the control animals were treated with a sham implant. Th e daily injection of rpST increased daily weight ga''m (P < 0.0001) an d decreased feed/gain ratio (P < 0.0001) and daily feed intake (P < 0. 0001). Barrows grew faster (P = 0.02) and ate more feed (P = 0.0001) t han gilts. On reaching - 100 kg, all pigs were slaughtered, and 60 pig s (two from each pen) were randomly selected for carcass evaluation. C arcass lean content was increased (P < 0.0001) and carcass fat content was decreased (P < 0.0001) in animals treated with rpST by daily inje ction. Animals treated with rpST by the slow-release implant were not different from the control animals in terms of growth performance and carcass characteristics. No overt lameness was observed in any of the pigs in the experiment. However, rpST treatment, regardless of the met hod of administration, increased the incidence and severity of osteoch ondrosis and reduced glycosanunoglycan concentration in the cartilage of the weight-bearing bearing area of humeral and femoral condyles. Th ese changes were independent of enhanced growth rate and carcass lean content. The results indicated that somatotropin treatment predisposes pigs to osteochondrosis.