Effect of protein deficiency on growth and plasma zinc concentration in genetically lean and obese swine.

Thirty-two genetically lean and 32 genetically obese weanling (4 to 5 wk old) pigs from inter se matings of crossbreds produced by within-line matings of Duroc and Yorkshire breeds, selected for low or high backfat, were fed the following four diets for 8 wk (eight lean and eight obese pigs/diet): 10% protein -- 100 ppm Zn, 10% protein -- 200 ppm Zn, 18% protein -- 100 ppm Zn, 18% protein -- 200 ppm Zn. After 8 wk, all pigs were fed a standard 16% protein corn-soybean meal-type growing diet to a slaughter weight of about 87 kg. Lean pigs were more severely affected than obese pigs by low protein diets as measured by weight gain, plasma total protein and plasma albumin. Plasma Zn concentration was reduced in lean and obese pigs fed low protein diets. Supplemental Zn failed to increase plasma Zn in protein-deficient pigs. During repletion, weight gain of lean and obese pigs previously fed the 10% protein -- 100 ppm Zn diet was less than that of pigs previously fed other diets. The lower level (100 ppm) of Zn fed during protein depletion appeared to be associated with a negative effect on repletion weight gain of lean and obese pigs. Lean and obese pigs responded similarly during the repletion phase to earlier protein restriction. We conclude that supplementary dietary Zn does not maintain plasma Zn concentration in growing pigs fed protein-deficient diets and that repletion from dietary protein restriction is not associated with compensatory growth in genetically lean pigs.