Effect of chronic immune system activation on body nitrogen retention, partial efficiency of lysine utilization, and lysine needs of pigs.

The influence of a low and high level of chronic immune system (IS) activation on body nitrogen retention, partial efficiency of dietary lysine utilization, and lysine needs of pigs at three body weights was determined. 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 or continuously exposing pigs to major vectors of antigen transmission. In each IS group, four littermate barrows in each of six litters were allotted at 25 d of age to one of four dietary amino acid regimens (.60, .90, 1.20, or 1.50% dietary lysine). Pigs were individually penned and allowed to freely consume feed from 6.2 to 26.5 kg BW. Nitrogen balance during 4-d periods was determined for each pig at BW of 10, 17.5, and 25 kg. Minimizing the level of chronic IS activation resulted in 4.7 to 7.7 g/d greater body nitrogen retention, 147 to 201 g/d greater BW gain, and 101 to 147 g more gain per kilogram of feed in pigs at the three BW. Dietary lysine intakes needed to maximize each of these criteria at BW of 10, 17.5, and 25 kg were a minimum of 2, 2, and 3 g/d greater in the low vs high IS pigs. However, the partial efficiency of lysine utilization for body nitrogen retention was similar between IS groups. On the basis of these data, the greater dietary lysine needs of the low IS pigs are due to their greater biological capacity for body nitrogen accretion and not to differences in their efficiency of dietary lysine utilization.