Lysine levels and ideal ratios of amino acids for finishing pigs

Abstract

Experiments were conducted to determine the ideal digestible lysine (Lys) requirements for early (EF = 50 to 90 kg) and late (LF = 90 to 110 kg) finishing barrows and gilts. The basal diets were reduced crude protein (CP), amino acid fortified basal diets which contained 11% and 10% CP for the EF and LF periods, respectively. Response criteria were fitted to a rectilinear "broken-line" model, and break-points were utilized to estimate a Lys requirement. Digestible Lys requirement estimates based on the average of the requirements for daily gain, gain:feed ratio, loin-eye area, 10th rib fat depth, lean gain, and plasma urea N were.58% for EF barrows and.64% for EF gilts. Digestible Lys requirement estimates based on the average of the requirements for daily gain, gain:feed ratio, lean gain, and plasma urea N were.49% for LF barrows and.52% for LF gilts.

A combined EF and LF growth trial and a LF metabolism trial were conducted to compare performance, carcass composition, and N retention of pigs fed diets containing either the ideal ratios of threonine (65%), tryptophan (18%), and sulfur amino acids (60%) to Lys for young pigs, or the ideal ratios of threonine (70%), tryptophan (20%), and sulfur amino acids (65%) to Lys proposed for finishing pigs. The proposed ratios for the finishing pig increased (P $<$.08) whole-body and carcass protein concentrations relative to the ideal ratios for young pigs, and also increased (P $<$.10) rates of protein accretion. In the metabolism trial, the proposed ratios increased (P $<$.05) all measures of N retention.

Two combined EF and LF growth trials were conducted to determine the effects of feeding two CP regimens on performance and carcass composition. Dietary treatments were the combination of a 14.5% CP diet in EF with a 13.5% CP diet in LF, or a 17.0% CP diet for both EF and LF. Diet effects were tested in two housing systems (Trial 1 = 2 pigs/pen with 2.2 m$\sp2$ of floor space/pig; Trial 2 = 9 pigs/pen with.65 m$\sp2$ of floor space/pig). Daily gain, gain:feed ratio, loin-eye area, and 10th-rib backfat were not affected by dietary treatment in either trial. Daily gain and daily lean gain were reduced in trial 2 relative to trial 1. Increased levels of Lys and CP had no effect on the performance or carcass composition of pigs raised under research or commercial conditions.