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Dietary Calcium and Phosphorus for Developing Boars^1,2,

The Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691

³ For reprint requests: Dept. of Anim. Sci., Ohio Agr. Res. and Develop. Center, Wooster 44691.

Abstract

An experiment of 3 x 3 factorial arrangement in a split-plot design was conducted using 216 crossbred boars to evaluate the effects of three dietary Ca/P levels (.65/.50, .90/.70, 1.17/.90%) from weaning to 20 kg and then from 20 to 110 kg, with measurements also collected at 55 kg body weight. Corn-soybean meal diets containing 20% protein were fed to 20 kg body weight followed by diets containing 18% protein until boars reached 110 kg body weight. Dicalcium phosphate and limestone were the dietary inorganic mineral sources. Daily gains and feed conversions improved at the higher Ca/P levels during the postweaning and early grower period. From 55 to 110 kg, gains were inverse to those in the earlier period, with boars fed the lower Ca/P levels having the highest gains. For the overall period from 7 to 110 kg, gains were similar for all treatment groups. Serum P increased and Ca decreased, both quadratically at the 3- and 6-wk postweaning period as Ca/P level increased; however, there were no treatment differences at 55 or 110 kg. Hydroxyproline levels in urine and serum at both 20 and 55 kg body weight were highest in pigs fed the lower mineral levels, implying greater collagen turnover. Bone ash values at each measurement period increased linearly as dietary Ca/P levels increased. A significant interaction of bone mineralization by dietary Ca/P level between the various growth intervals occurred. Boars fed .65/.50% dietary Ca/P during the postweaning period had lower bone ash concentrations at 55 kg body weight regardless of mineral level fed from 20 to 55 kg; whereas when the two higher dietary Ca/P levels were provided during the postweaning period, bone mineralization was similar at 55 kg body weight. The effects of postweaning dietary mineral levels were not observable at 110 kg, suggesting complete compensatory bone mineralization.

¹ Approved for publication as Journal Article 212-81 of The Ohio Agr. Res. and Develop. Center and The Ohio State Univ., Wooster.

² Appreciation is expressed to T. Hartman and R. Todd for their help in the collection of data and samples and to Dr. J. Holman for the Statistical analysis.

⁴ Present address: Tindle Mills, Inc., Springfield, MO 65801.

⁵ Dept. of Anim. Sci., The Ohio State Univ., Columbus.