EFFECT OF DIETARY CALCIUM AND PHOSPHORUS LEVELS ON PERFORMANCE, BONE BENDING MOMENT AND THE SEVERITY OF OSTEOCHONDROSIS AND LAMENESS IN BOARS AND GILTS SLAUGHTERED AT 100 OR 130 KG BODY WEIGHT

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Abstract
Ninety-six crossbred gilts and 96 crossbred boars averaging 20 kg were assigned to a factorial arrangement of three dietary calcium-phosphorus (Ca-P) levels and two slaughter weights (100 or 130 kg). The Ca-P regimens were based on (1) National Academy of Sciences-National Research Council (NAS-NRC)(1979), (2) Agricultural Research Council (ARC) (1981) and (3) 130% of ARC (1981) recommendations for grower and finisher swine. All pigs were fed ad libitum grower diets (0.60–0.50, 0.81–0.63, 1.05–0.82% Ca-P) from 20 to 55 kg and finisher diets (0.50–0.40, 0.72–0.54, 0.94–0.70% Ca-P) to 100 kg or 130 kg liveweight. At 100 kg liveweight 16 boars and 16 gilts from each of the Ca-P treatment groups were selected at random and slaughtered. The remaining pigs within each Ca-P group were allowed feed ad libitum or at 70% of ad libitum from 100 kg until slaughter at 130 kg. There was no significant effect of the three respective dietary Ca-P regimens on average daily gain, average daily feed intake, or feed/gain ratio of pigs during the 20- to 100-kg growth period. Metacarpal bending moment and femoral ash content increased (P < 0.05) in response to the first dietary Ca-P increment. There was a significant (P < 0.05) positive response of femoral ash content but not of bone bending moment to the second Ca-P increment. The incidence and severity of osteochondrosis of the femur, humerus, radius and ulna and leg soundness scores were unimproved (P > 0.05) by feeding elevated dietary Ca-P levels. There was no significant effect of ad libitum vs. restricted feeding during the 100- to 130-kg growth period on bone ash, bone bending moment or cartilage condition scores. Boars had significantly (P < 0.01) greater average daily gain and lower feed/gain ratio during the 20- to 100-kg growth period but they had more severe (P < 0.01) osteochondrotic lesions of the elbow joint and a lower (P < 0.001) femoral ash content than gilts. Correlation coefficients between cartilage soundness scores and bone ash content or bending moment were nonsignificant (P > 0.05). The results suggest that while bone ash content and bending moment respond positively to elevated Ca-P levels in excess of NAS-NRC (1979) recommendations, the incidence and severity of joint lesions and leg soundness scores are not reduced by maximizing bone mineralization. Key words: Osteochondrosis, calcium, phosphorus, swine