Effects of adding fiber sources to reduced-crude protein, amino acid-supplemented diets on nitrogen excretion, growth performance, and carcass traits of finishing pigs12

Two experiments were conducted to evaluate the effects of adding fiber sources to reduced-crude protein (CP), amino acid-supplemented diets on N excretion, growth performance, and carcass traits of growing-finishing pigs. In Exp. 1, six sets of four littermate barrows (initial weight = 36.3 kg) were allotted randomly to four dietary treatments to determine N balance and slurry composition. Dietary treatments were: 1) fortified corn-soybean meal, control, 2) as fortified corn-soybean meal with CP lowered by 4 percentage units and supplemented with lysine, threonine, methionine, tryptophan, isoleucine, and valine (LPAA), 3) same as Diet 2 plus 10% soybean hulls, and 4) same as Diet 2 with 10% dried beet pulp. Nitrogen intake, absorption, and retention (g/d) were reduced (P 0.10) by addition of fiber sources to the LPAA diet. However, N absorption, as a percentage of intake, was not affected (P > 0.10) by dietary treatment. Nitrogen retention, expressed as a percentage of N intake, was increased (P 0.10) by fiber addition. However, fiber addition to the LPAA diet tended to result in a greater proportion of N excreted in the feces than in the urine. Slurry pH, ammonium N content, and urinary urea N excretion were reduced (P 0.10) by dietary treatment. These data suggest that reducing CP with amino acid supplementation markedly decreased N excretion without influencing growth performance. Fiber addition to a LPAA diet had little effect on overall N balance or growth performance, but tended to further reduce slurry ammonium N concentration and increase volatile fatty acid concentrations.