A 3-week post-weaning restricted feeding as alternative to an ad libitum antibiotic-medicated feed: Effects on growth, carcass and meat of rabbits differing in genotype and slaughter age

In this investigation, the impact of a 3-week post-weaning restricted feeding (RF) using an antibiotic-free feed, applied to rabbits from 36 to 56 days of age to preserve their health status as alternative to an ad libitum medicated feed with antibiotics (AMF), was verify in relation to rabbit genotype and slaughter age (SA). The RF and AMF treatments were compared evaluating their effects on feed intake, growth, mortality, carcass and meat quality of rabbits of two genotypes, Italian White purebred (IWP) and hybrid Hycole×IWP crossbred (HIWC), slaughtered at 78 or 92 days of age to obtain light or heavy carcasses. At 36 days of age, 256 weaned rabbits of both sexes were divided into 4 homogeneous groups based on feeding treatment (FT) and genotype: RF-IWP, RF-HIWC, AMF-IWP and AMF-HIWC. The RF treatment was performed offering to each rabbit 70, 80 and 90 g/day of feed in the 1st, 2nd and 3rd week. After the 3-week RF and AMF treatments, all rabbits received the same ad libitum antibiotic-free feeds until their slaughter. For each group, 24 rabbits were slaughtered, 12 at 78 days and 12 at 92 days. On the whole feed intake with RF was equal to 63% of that with AMF. Regardless of genotype, RF was associated with a lower feed intake until 78 days and a compensatory growth from 58 to 78 day, whereas from 79 to 92 days intake was not affected by FT and genotype. Despite the compensatory growth, the lower intake of restricted rabbits resulted in lower live weight at 78 and 92 days, but in more favourable feed conversion than with AMF. The growth potential allowed the crossbred rabbits to reach higher body and carcass weights with more efficient feed utilization. Mortality for enteropathies occurred mainly during the post-weaning phase from 36 to 56 days of age, with no difference due to FT, whereas HIWC rabbits showed a lower resistance to enteropathies. Heavier and fatter carcasses were obtained from AMF rabbits, at both SA, whereas the heavier HIWC carcasses showed a lower fat content than IWP ones. Carcass yield was influenced by FT and SA, being lower in RF rabbits and at earlier age. The restriction affected some colour indexes of meat and induced lower adiposity. Collagen was higher in meat of 92-day rabbits and in males, with no relationship to shear force. No particular effect of genotype emerged for meat quality. On the whole a 3-week post-weaning RF with antibiotic-free feed is confirmed to be a suitable method to replace an ad libitum feed containing antibiotics. In addition, RF appeared more suitable for rabbits of high-growth genotype slaughtered at 92 days which were more effective to recover the growth slowing due to the post-weaning feed restriction