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 con centration, 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 i nitial body composition. The remaining 60 pigs were allotted to a randomize d complete block (RCB) experiment with a 2 x 5 factorial arrangement of tre atments (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 b locks of pigs (30 total) were selected randomly and slaughtered. Feed intak e decreased with increasing protein concentration (linear, P < .05), and th e reduction was greater in gilts than in barrows (P < .05). There was a tre nd 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 accr etion decreased linearly as protein level increased (P < .05). Increased pr otein concentrations increased liver, kidney, and pancreas weights (linear, P < .05). Plasma urea concentration increased with each protein concentrat ion, 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 consistin g of a 2 x 2 factorial arrangement of treatments with two sexes and two die tary protein concentrations (16 and 25% CP). The experiment was terminated when the average BW of pigs reached 105 kg. Average daily feed intake was g reater (P < .10) in barrows than in gilts. Average daily gain was reduced b y 18% in gilts when dietary protein was increased from 16 to 25% but was on ly reduced 3% in barrows (sex x protein, P < .10). Barrows had lighter live rs (P < .005), greater arginase activities (P < .05), and greater plasma ur ea concentrations (P < .005) than did gilts. Increasing dietary protein con centration from 16 to 25% increased liver weight, arginase activity, and pl asma urea concentration (P < .005). These data suggest that gilts are more sensitive than barrows to excessive intakes of protein. The more negative e ffects in gilts may be related to liver metabolic capacity and activity of urea cycle enzymes.