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Phosphorus in Swine. II. Influence of Dietary Calcium and Phosphorus Levels and Growth Rate on Serum Minerals, Soundness Scores and Bone Development in Barrows, Gilts and Boars¹

Virginia Polytechnic Institute and State University, Blacksburg 24061

Abstract

The influence of dietary Ca and P growth rate from birth to 60 to 70 days of age on serum minerals, soundness scores and bone development was evaluated with crossbred gilts and barrows or boars. The following dietary treatments, as percentages of NRC recommendations for barrows and gilts, were used: (1) 100% Ca and P, (2) 125% Ca and P, (3) 100% Ca and 125% P and (4) 100% Ca and 75% P. Pigs were fed an 18, 16 and 14% protein sequence. Final weight was 107 kilograms. Serum inorganic P concentration was depressed (P<.05) when pigs were fed a diet containing 100% Ca and 75% P as opposed to 100% Ca and P, but was not consistently increased when pigs were fed 125% P with 100 or 125% Ca. In cases where the magnitude of the P depression was greatest, serum Ca and Mg concentrations were increased. Serum Ca, P and Mg were not consistently affected by sex or growth rate. Pad, feet and leg, structural soundness and foot scores were generally not influenced by dietary Ca and P levels or growth rate. Gilts tended to be more sound than barrows, with no difference observed between boars and gilts. Bone development, as measured by metacarpal and mandible dried weight, ash and breaking load, was reduced when 75% of NRC-recommended P was fed, but it was not consistently increased when 125% P was fed. The maximum response occurred when 125% P was fed in combination with 125% Ca. Where increases were observed, the magnitude was small. Metacarpal and mandible parameters were equally responsive to dietary Ca and P levels, with ash slightly more responsive than dried weight or breaking strength. Tooth ash and Ca and P content of tooth ash were unchanged by any of the Ca and P levels. Metacarpal dried weight and breaking load were higher and ash lower for boars than for gilts. Growth rate had little effect on bone development. These results show that (1) serum P and bone mineralization (except tooth) of barrows, boars and gilts were reduced when less than NRC-suggested levels of P were fed; (2) pad, foot and overall soundness scores were not influenced by growth rate or dietary Ca and P levels; (3) barrows, boars and gilts appeared to respond in a similar manner to higher-than-NRC-suggested levels of Ca and P, and (4) maximization of bone development occurred when pigs were fed 125% P in combination with 125% Ca.

¹ Appreciation is expressed to Charlie Babb, Carl Eure and K. L. Bryant for feeding and caring for the pigs; to Helen Bartlett for analytical work; to Cindy Atkins for typing the manuscript; to Dr. K. H. Hinkel-mann and Bill Woodall for statistical analysis; to Smith-Douglass, Division of Borden Chemical, Borden, Inc., for partial financial support, and to L. B. Allen, J. H. Carter, S. Britt, J. Parker and R. Updike for evaluating the soundness of the pigs.

² Dept. of Anim. Sci.

³ Tidewater Research and Continuing Education Center.