Porcine somatotropin and dietary lysine influence bone mineralization and mechanical properties of bones in finishing swine.

The femur, a rib, and a third metacarpal were collected from 108 barrows (initial weight = 57 kg) and analyzed to determine the effects of porcine somatotropin (pST) and dietary lysine on bone mineralization and mechanical properties. In Exp. 1, pigs were injected daily with 4 mg of pST and fed diets containing 1.0% Ca and .9% P and either .6, .8, 1.0, 1.2, or 1.4% lysine. Control pigs (placebo injection) received the .6% lysine diet. Bone wall thickness (BWT) of the femur increased (linear, P < .05) but ash content decreased (linear, P < .10) as dietary lysine level increased. Stress and ash content of the rib also decreased (linear, P < .05) with increasing dietary lysine level. In Exp. 2, pigs were injected with either 4 or 8 mg/d of pST and fed diets containing 1.1% Ca and 1.0% P and either .8, 1.0, 1.2, or 1.4% lysine. Control pigs received the .8% lysine diet. Increasing pST dosage increased BWT of the femur (linear, P < .10) but decreased ash content (linear, P < .10). In the rib, increasing pST dosage reduced stress, modulus of elasticity (linear, P < .10), and ash content (linear, P < .01). Increasing lysine level resulted in increased BWT of the femur and decreased ash content of rib, femur, and metacarpal (linear, P < .10). These data indicate that pST administration in conjunction with increasing lysine levels decreases bone ash content but increases BWT of finishing pigs.