Effect of compensatory growth on performance, carcass composition and plasma IGF-1 in grower finisher pigs

A total of 48 female pigs (Large White × Landrace × Duroc cross) were used to determine whether a compensatory feed regime influenced performance, carcass composition and the level of plasma IGF-1. Pigs of initial age 73 days were fed a commercial diet at 0.70 of ad libitum (R) for 40 days followed by a return to ad libitum feeding for a further 42 days. The control group was fed ad libitum (A) throughout. Groups of animals on R and A feed regimes were slaughtered at the end of restriction period (SL1), 2 days after refeeding ad libitum (SL2) to establish the more immediate effects of refeeding on IGF levels, and after 42 days refeeding (SL3; n = 8 for each group). As expected, during the restriction period, average daily live weight gain in all the slaughter groups of R pigs was significantly lower than A pigs (P < 0.01); there was no significant difference in feed conversion ratios. In the re-alimentation period of SL3, R pigs grew 12.9% faster (P = 0.033), indicating compensatory growth. At SL1, there was a trend for carcass weight (P = 0.108) of A pigs to be higher than R pigs, but at SL2 live weight and carcass weight of A pigs were significantly heavier than R pigs (P < 0.05), but not at SL3. For killing-out percentage, there was no difference in SL1. After refeeding for 2 days (SL2) and 42 days (SL3), R pigs had significantly lower killing-out percentage than A pigs (P < 0.05). As a proportion of live weight, R pigs had smaller heart, kidney and liver (P < 0.05) than A pigs at SL1. At SL2, only the kidney was smaller in the restricted group (P < 0.05) and there were no significant differences in SL3. As a proportion of carcass weight, Longissimus dorsi was heavier in the R pigs at SL1 (P = 0.108) and SL2 (P < 0.05), but not at SL3. At SL1, there was a trend for intramuscular fat of A pigs to be higher than R pigs. The plasma IGF-1 level was lower in R pigs than A pigs (P = 0.010) at SL1, and slightly lower at SL2 (P = 0.110), with no significant differences at SL3. Dietary restriction period influenced plasma IGF-1 levels, which returned to the ad libitum group levels when animals were refed, as did live weight and carcass weight. It appears that the internal organs and possibly fat, but not muscles, underwent a compensatory response when animals were refed.