Biological characteristics for assessing low phosphorus intake in finishing swine

Three replicates of a randomized complete-block design in a 3 x 3 factorial arrangement of treatments involving 141 pigs were conducted to evaluate the effect of low P intake on various response criteria in swine from 65 to 95 kg body weight. Total dietary P levels of .09, .21 and .31% were each fed in a Ca:P ratio of 1.1, 1.5:1 or 2:1 for a 35-d experimental period. The basal diet was formulated using corn starch, dextrin and a soy protein concentrate with monosodium phosphate and limestone supplying desired treatment levels of Ca and P. Blood and bones were collected for mineral analysis. Gain and feed performance responses were not affected by Ca:P ration or dietary P level for the 35-d period. Serum inorganic P concentrations declined as Ca:P ratio increased, but increased as dietary P increased. Serum alkaline phosphatase activity increased with higher Ca:P ratios, and decreased as dietary P level increased. Percent bone ash was not influenced by Ca:P ratio, but increased as dietary P level increased. Bone-bending moment was influenced by Ca:P ratio, and increased linearly as dietary P increased. Dietary P level resulted in a linear increase in total bone and its ash component weight, and in the accretion of the ash and organic matrix component. These data suggest that between 65 to 95 kg body weight, percent bone ash was affected by dietary P level, while bone-bending moment, bone component weights, their accretion, both dietary p level and Ca:P ratio.