Effect of level of chronic immune system activation on the growth and dietary lysine needs of pigs fed from 6 to 112 kg.

The effect of a low and a high level of chronic immune system (IS) activation on the rate, efficiency, and composition of body growth and dietary lysine needs of pigs fed from 6 to 112 kg body weight was evaluated. All pigs were of a single genetic strain and geographical site of origin, and the low and high IS pigs were created by physically isolating pigs from and continually exposing pigs to major vectors of environmental antigen transmission. In each IS group, five littermate barrows from each of seven litters were individually penned and randomly allotted to one of five dietary amino acid regimens (.6, .9, 1.20, 1.50, and 1.80% lysine from 6 to 27 kg BW and .45, .60, .75, .90, and 1.05% lysine from 27 to 112 kg BW). Dietary lysine concentrations were achieved by altering the ratio of corn to soybean meal in the diets, and diets were formulated such that lysine was the first-limiting amino acid. Low IS pigs possessed lower (P < .01) T lymphocyte CD4+:CD8+ ratios and serum alpha-1-acylglycoprotein concentrations. Low IS pigs also consumed more (P < .01) feed, gained body weight faster (P < .01), required less (P < .01) feed per unit of gain, and at 112 kg BW produced bodies with more (P < .12) muscle and less (P < .10) fatty tissue and offal than high IS pigs. To allow their elevated capacities for proteinaceous tissue to be expressed, low IS pigs required .15 to .30 percentage units greater dietary lysine concentrations and 2 to 5 g higher daily lysine intakes at each 14-kg BW increment from 6 to 112 kg BW.