Possible effects of the MC4R Asp298Asn polymorphism on pig production traits under ad libitum versus restricted feeding

The missense mutation Asp298Asn in the melanocortin 4 receptor (MC4R) is associated with daily gain or fatness in pigs (Sus scrofa domesticus). However, to the best of our knowledge, no study has directly compared the effects of the polymorphism between different feeding levels, even though diet plays a vital role in the swine industry. To explore possible differences, data from 439 mostly commercial hybrids fattened ad libitum and 119 commercial hybrids fattened with restricted feed ration were collected. The recorded traits were average daily gain (ADG), feed conversion ratio (FCR), carcass weight (CW), dressing percentage (DP), lean meat content (LM), backfat thickness (BFT), lean cuts weight, and meat quality parameters such as pH, temperature, drip loss, and CIELAB colour space. The general linear model revealed that the overall effect of MC4R was not statistically significant, but significant differences (p < 0.05) were found in ADG, FCR, CW, DP, LM, and BFT. In the ad libitum category, the AA genotype (298Asn/298Asn) tended to be the most favourable for growth-related traits, with the lowest LM, which is consistent with previous findings. In the restricted category, on the other hand, GA heterozygotes (298Asp/298Asn) achieved the best performance in terms of growth, whereas AA homozygotes showed the worst performance. Therefore, these results raise the possibility of an interaction between MC4R and the feeding level.