Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/18/2003
Publication Date: 12/1/2003
Citation: Kerr, B.J., Southern, L.L., Bidner, T.D., Friesen, K.G., Easter, R.A. 2003. Influence of dietary protein level, amino acid supplementation, and dietary energy levels on growing-finishing pig performance, and carcass composition. Journal of Animal Science. 81:3075-3087. Interpretive Summary: The use of low crude protein, amino acid-supplemented diets can reduce feed costs and dramatically lower the amount of nitrogen excreted into the environment. However, pigs fed low crude protein, amino acid-supplemented diets have been shown to have fatter carcasses compared with pigs fed high crude protein diets. The increased fatness in pigs fed low crude protein, amino acid-supplemented diets partially may be due to more dietary energy being available for fat synthesis as a result of reduced energy expenditure for catabolization of excess dietary protein. In fact, excess crude protein intake has been shown to increase energy expenditure and impact organ size and energy metabolism. In addition, reduced plasma urea nitrogen observed in pigs fed the low crude protein, amino acid-supplemented diet provides another indicator of a reduced energy need for deaminating excess amino acids. In laboratory-based experiments, researchers in France and the United States have reported that pigs fed a reduced-crude protein, amino acid-supplemented diet had a lower heat production than pigs fed a higher crude protein diet. In heat stress conditions, improved growth performance by feeding diets formulated to minimize amino acid excesses has been observed in chicks and pigs. The results of the current experiments indicated that low crude protein (3% reduction), amino acid-supplemented diets can be fed with no serious adverse effects on growth, gain:feed, or carcass traits. The data did not support the notion that feeding a low crude protein, amino acid-supplemented diet will make a discernable impact on pig performance or carcass composition in pigs maintained in heat-stressed environments. Research results described in this report provides nutritionists at universities, feed companies, and swine production units vital data that growing-finishing pigs fed low crude protein-amino acid supplemented diets will perform similar and have carcasses with similar composition compared to pigs fed high crude protein diets.
Technical Abstract: Two experiments were conducted to determine the effects of feeding reduced CP, AA-supplemented diets at two ambient temperatures (Experiment 1) or three levels of dietary NE (Experiment 2) on pig performance and carcass composition. In Experiment 1, 240 crossbred pigs were used to test whether projected differences in heat increment associated with diet composition would affect pig performance. There were 10 replications of each treatment with four pigs per pen. For the 28-d trial, the average initial and final BW were 28.7 kg and 47.5 kg, respectively. Pigs were maintained in a thermal-neutral (23¿C) or heat-stressed (33¿C) environment and fed a 16% CP diet, 12% CP diet, or a 12% CP diet supplemented with crystalline Lys, Trp, and Thr. Pigs gained at similar rates when fed the 16% CP diet or the 12% CP diet supplemented with Lys, Trp, and Thr (P > 0.10). Pigs fed the 12% CP, AA-supplemented diet had a similar gain:feed compared with pigs fed the 16% CP diet when housed in the 23¿C environment, but a lower gain:feed in the 33¿C environment (diet x temperature, P < 0.01). In Experiment 2, 702 gilts were allotted to six treatments with nine replicates of 13 gilts each. Average initial and final BW were 25.3 and 109.7 kg, respectively. Gilts were fed two levels of CP (high CP with minimal crystalline AA supplementation or low CP with supplementation of Lys, Trp, Thr, and Met) and three levels of NE (high, medium, or low) in a two by three factorial arrangement. A four phase feeding program was used with diets containing apparent digestible Lys levels of 0.96, 0.75, 0.60, and 0.48% switched at 41.0, 58.8, and 82.3 kg BW, respectively. Pigs fed the low CP, AA-supplemented diets had similar rates of growth and feed intake as pigs fed the high CP diets. Dietary NE interacted with CP level on gain:feed (P < 0.06). A reduction in dietary NE from the highest NE level reduced gain:feed in pigs fed the high CP diet; however, gain:feed declined in pigs fed the low CP, AA-supplemented diet only when dietary NE was reduced to the lowest level. There was a slight reduction in longissimus area in pigs fed the low CP diets (P < 0.08), but other estimates of carcass muscle did not differ (P > 0.10). The data suggest that pigs fed low CP, AA-supplemented diets will have similar performance and carcass characteristics as pigs fed higher levels of CP and alterations in dietary NE will not have a discernable impact on pig performance or carcass composition.