The effect of excess protein on growth performance and protein metabolism of finishing barrows and gilts.

Two experiments were conducted to evaluate the effect of excess protein on growth performance, carcass characteristics, organ weights, plasma urea concentration, and liver arginase activity of finishing barrows and gilts. In Exp. 1, 35 barrows and 35 gilts with an initial BW of 51 kg were used. Five pigs of each sex were slaughtered at the start of the study to determine initial body composition. The remaining 60 pigs were allotted to a randomized complete block (RCB) experiment with a 2x5 factorial arrangement of treatments (two sexes x five protein levels: 13, 16, 19, 22, and 25% CP). The experiment continued until the average BW was 115 kg, at which time three blocks of pigs (30 total) were selected randomly and slaughtered. Feed intake decreased with increasing protein concentration (linear, P<.05), and the reduction was greater in gilts than in barrows (P<.05). There was a trend toward a linear negative effect of dietary protein on ADG (P<.10) and also a quadratic effect of protein on protein accretion (P<.10). Fat accretion decreased linearly as protein level increased (P<.05). Increased protein concentrations increased liver, kidney, and pancreas weights (linear, P<.05). Plasma urea concentration increased with each protein concentration, with the exception of the 25 vs. 22% CP treatment in gilts. In Exp. 2, 18 barrows and 18 gilts (BW 63 kg) were allotted to an RCB design consisting of a 2x2 factorial arrangement of treatments with two sexes and two dietary protein concentrations (16 and 25% CP). The experiment was terminated when the average BW of pigs reached 105 kg. Average daily feed intake was greater (P<.10) in barrows than in gilts. Average daily gain was reduced by 18% in gilts when dietary protein was increased from 16 to 25% but was only reduced 3% in barrows (sex x protein, P<.10). Barrows had lighter livers (P<.005), greater arginase activities (P<.05), and greater plasma urea concentrations (P<.005) than did gilts. Increasing dietary protein concentration from 16 to 25% increased liver weight, arginase activity, and plasma urea concentration (P<.005). These data suggest that gilts are more sensitive than barrows to excessive intakes of protein. The more negative effects in gilts may be related to liver metabolic capacity and activity of urea cycle enzymes.