Effect of Increasing Dietary Protein Level, Calcium and Phosphorus on Feedlot Performance, Bone Mineralization and Serum Mineral Values with Growing Swine2

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Abstract
Three experiments were conducted to evaluate the effects of increasing dietary protein level, calcium and phosphorus on feedlot performance, serum mineral levels and bone ash in g rowing swine from 20 to 55 kilogram. Fortified corn-soybean meal diets were formulated to contain protein levels from 14 to 22%. Calculated dietary calcium and phosphorus were maintained at a 1.3:1 ratio for all treatments. The base level of these minerals was .65% calcium and .50% phosphorus with additional treatments increasing at .25 and .20% increments, respectively. In the first two experiments when total dietary calcium and phosphorus levels were maintained at the base level and dietary protein level was increased, growth rate, feed intake, bone ash and total carcass protein and ash content declined when the higher dietary protein levels were fed, particularly above the 18% protein level. Serum phosphorus declined and serum calcium increased in an inverse relation to one another as dietary protein was raised. Serum alkaline phosphatase activity was higher when a 22% protein diet was fed as compared to either a 14 or 18% diet. Evidence of osteoporosis was observed in the long bones from pigs fed the 18th diet with the severity increasing when the 22% protein level was fed. When dietary calcium and phosphorus were elevated in either a 16 or 22% protein diet, increased growth resulted as did serum phosphorus and bone ash. Serum phosphorus declined within 24 hr after the trial started when the base mineral level was fed at either dietary protein level, whereas other treatments had more stable values. In general, however, serum phosphorus levels for those pigs fed the 22% diet were lower throughout the experiment as compared to the same mineral level at 16% protein. Serum phosphorus values increased by 3 and 6 weeks for the lower mineral diets with treatment differences becoming less apparent as the experiment progressed. By 55 kg body weight, bone ash results curvilinearly increased and plateaued up to the calcium and phosphorus levels of .90 and .70%, respectively, when the 16% protein diet was fed but continued to increase to the highest mineral level (1.15 and .90%, respectively) when the 22% diet was offered. Serum magnesium did not appear to be influenced by any of the dietary treatments. Copyright © 1976. American Society of Animal Science . Copyright 1976 by American Society of Animal Science