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Virginia Polytechnic Institute and State University, Blacksburg 24061
Abstract
Eighty crossbred boars were utilized in a 2 x 2 factorial arrangement of two energy levels (ad libitum and 75% ad libitum) and two Ca/P levels (100 and 150% of National Research Council daily requirement) to determine the effect of varying growth rate and Ca/P intake on performance and bone characteristics throughout the growth phase. Boars were fed the diets beginning postweaning at 5 wk of age and continuing until necropsy at 10 ± 2-d intervals between 80 and 220 d of age, inclusive. Body weight of limit-fed boars was 72% that of ad libitum-fed boars. Daily gain and feed per gain ratio favored boars fed the 150% Ca/P levels. Although limit-feeding enhanced the development of longer, thicker and heavier metacarpals earlier in the growth period (between 80 and 150 d of age), there was little difference between limit-fed and ad libitum-fed boars at 220 d of age when values were corrected for differences in body weight. Mechanical bone characteristics, which were greater for ad libitum-fed than for limit-fed boars at the same age, were not different when values were corrected for body weight. Boars fed 150% Ca/P levels had heavier and thicker walled metacarpals that had greater bone strength than boars fed 100% Ca/P levels, with the magnitude of the difference not as great at 220 d of age and when values were corrected for body weight. Generally, boars fed the ad libitum-150% Ca/P diet had the heaviest and strongest bones. Ether extract, ash and Ca and P content of ash were generally higher for ad libitum-fed vs limit-fed and 150 vs 100% Ca/P diets at 80 and 150 d of age, but were not different at 220 d. Metacarpal weight, size, thickness, strength and ash content increased with age with a small decline in the rate of increase. Ether extract decreased with age. There was a very small increase in the Ca content of ash and a very small decrease in the P content with age, resulting in a slightly wider Ca:P ratio in older boars.
1 Appreciation is expressed to the John Lee Pratt Animal Nutrition Program for financial support, to Deborah Tanguy and Helen Bartlett for laboratory assistance, to Ken Bryant and Duke Reynolds for animal care, to David Calabotta for assistance in collecting data, to Dr. J. L. Baker for help in determining bone mechanical properties, and to Ellie Stephens and Cindy Eaton for manuscript preparation.
2 Dept. of Anim. Sci., Virginia Polytechnic Institute and State Univ.
3 Division of Veterinary Pathology and Public Practice, Virginia-Maryland Regional College of Veterinary Medicine.
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