Effects of recombinant porcine somatotropin (rpST) on joint cartilage and axial bones in growing and finishing pigs

Abstract

Seventy-two gilts (PIC, Cambourough) weighing 20 kg were allocated to four pens, each with two electronic feeders. After a 20-d conditioning period, eight pigs (two pigs/pen) were slaughtered for initial carcass measurements. The remaining pigs in each pen, at an average liveweight of 33.0 ± 2.49 kg (mean ± SD), were randomly assigned to three treatments: daily saline injection (control), daily injection of recombinant porcine somatotropin (rpST) (100 μg kg−1 liveweight) and a treatment group in which rpST injected pigs were switched to a saline injection at approximately 63 kg liveweight (withdrawal). Eight control and eight rpST-treated pigs, two from each pen were slaughtered at an average liveweight of 62.8 ± 3.72 kg, and the remaining pigs were slaughtered at 100.3 ± 5.51 kg. Daily injection of rpST increased the average concentration of plasma somatotropin but did not increase the width of distal ulna epiphysis. Vertebrae and ribs of pigs injected with rpST from 33.0 to 100.3 kg liveweight showed a higher water content (P < 0.01), a lower ash content of moisture-free bone (P < 0.05), and lower dry matter (P < 0.01) and ash (P < 0.001) densities than those of control pigs. Withdrawal of rpST injection at 62.8 kg liveweight abolished the effect of rpST on all bone properties except for the ash density. Injection of pigs with rpST from 33.0 to 100.3 kg resulted in higher (P < 0.05) humeral condyle lesion score and decreased average concentrations of uronic acid (P < 0.05) and hydroxyproline (P < 0.005) in cartilage from both distal humeral and femoral condyles but had no significant effect on the ratio of uronic acid to hydroxyproline compared with control animals. Withdrawal of rpST treatment at 62.8 kg diminished the effect of rpST on cartilage soundness and uronic acid and hydroxyproline concentrations of the joint cartilage. The long-term use of rpST reduced chondrocyte metabolism, which may indirectly reduce compressive and tensile strength of cartilage and increase susceptibility to mechanical stress, leading to osteochondrosis. Key words: Osteochondrosis, growth rate, recombinant porcine somatotropin, bones, pigs