Maintenance feeding of 100 kg pigs: effect on carcass lean and fat yield and on gastrointestinal organ size

Abstract

AbstractThe study was conducted to test the hypotheses that sustained restriction of food to maintain constant body weight of market-ready pigs, hereafter terminal maintenance (TM), would (1) decrease the size of gastrointestinal and other visceral organs, (2) increase dressing proportion, and (3) increase lean and decrease fat content and improve the lean: fat ratio of carcass. Forty-eight crossbred castrated male pigs (initial body weight, 23·5 kg) were randomly assigned to eight treatment groups (six pigs per group; one pig per pen). Three comparison groups were included. Thead libitumcontrol group (AL) was slaughtered at the target weight, 105 kg. One group was continuously restricted (CR) to 0·8 of the intake by AL and slaughtered at the target weight. The terminally restricted (TR) group was given food ad libitum to 1·1 times the target weight; then food was restricted to effect weight loss to the target weight before slaughter. Five TM groups were given food ad libitum to the target weight; then TM was administered for various periods (7, 14, 21, 28 and 42 days) before slaughter. CR either had no effect or caused enlargement of visceral organs compared with AL. TR caused reduction of viscera, especially of abdominal-digestive organs. TM caused reduction of most viscera organs (0·001 <P< 0·05). Regression analyses indicated that most abdominal organs were reduced 50 to 70 g/kg per 10 days of terminal maintenance. TM and TR also increased carcass weight (P< 0·05). Catabolism associated with reduction of viscera organs may provide nitrogenous substrates to support the continued lean accretion observed during terminal maintenance. The reduced viscera and increased carcass weight combined resulted in increased dressing proportion (P= 0·06). Regression analyses (weightv.TM-days) showed that lean mass increased (71 g/day;P< 0·05) and fat mass decreased (−52 g/day;P< 0·01). Weight of bone and belly did not change. Differential lean gain, lean gain minus fat gain, during TM occurred at a rate of about 120 g/day.