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An experiment was conducted to examine the effects of compensatory growth and amino acid supply on organ weights and carcass characteristics in growing gilts. Gilts were fed either a corn-soybean meal diet or a corn-soybean meal diet supplemented with crystalline lysine. Pigs were randomly allotted to either a 21-day ad libitum eating period or a 42-day restricted-realimentated feeding period. The restricted-realimentated (RR) feeding period consisted of a 21-day restriction period and a 21- day ad libitum eating period (realimentation). During the restriction period, pigs were fed to maintain body weight. Results indicated that during the restriction period, gilts had a decrease (P < 0.01) in the weight of the liver, kidneys and small intestine. During the first week of ad libitum eating, organ weights of gilts in the RR group increased dramatically. Weights of the liver and stomach of gilts in the RR group were greater (P < 0.05) than the ad libitum (AL) fed gilts during week one of ad libitum eating. In addition, weights of the kidneys, small intestine and mesentery were not different between feeding regimens after the first week of ad libitum eating. Carcass and ultrasound measurements taken before and after the restriction period showed a numerical decrease in tenth-rib backfat and an increase in longissimus muscle area during the 21-day restriction period. These measurements are consistent with the decrease (P < 0.01) in the percentage of carcass fat and an increase (P < 0.05) in carcass protein percentage caused by restricted feeding. Although the carcass protein percentage was greater in the RR gilts at the start of the ad libitum eating period, carcass protein accretion was greater (P < 0.01) in the AL gilts versus the RR gilts during weeks one and two of ad libitum eating. Gilts in the RR group exhibited compensatory organ growth during the first week of the ad libitum eating period. Also, during a restriction period, growing gilts are able to use fat stores and repartition visceral protein to maintain lean muscle deposition.
Growing pigs often face environmental and health challenges which limit energy and nutrient intake. This research has identified that protein from liver and other visceral depots can be used to help provide amino acids for muscle growth during prolonged feed restriction. Also, the weight and composition of visceral organs are restored quickly when refeeding commences. Because these tissues account for a significant portion of pig’s daily energy requirement, fundamental knowledge documenting how key organs respond to energy and nutrient intake will ultimately help provide insight into how pigs will adapt to specific nutritional regimens. Additional research is needed to see how organs and muscle adaptations change as the pig progresses through the growing and finishing phases.