Growth Promoters in Rabbits

Fifty-six weanling crossbred rabbits (NZW x Native), aged 28 days, were randomly allotted to 7 groups with 8 animals per treatment and 2 animals per cage. Their diet was calculated to contain 16% crude protein with 3,300 kcal of digestible energy / kg feed. Para grass was fed ad libitum. Oxytetracycline and virginiamycin were added to the feed at levels of 5, 10 and 20 and 10, 20 and 40 mg/kg respectively and the seventh group was used as a control. Weight gain and feed intakes were recorded weekly for 10 weeks. Four rabbits from each group were slaughtered for carcass evaluation and their hindquarters were frozen for antibiotic residue testing, using the EEC-four plate method. The rest of the animals were killed after the antibiotics had been withdrawn for 7 days and tested for antibiotic residues. All the data was analyzed using Analysis of Variance and Duncan's New Multiple Range test. There were no difference in the growth rate or the feed conversion ratio in all the groups during the first 7 weeks of the experiment. In the 8th week, groups supplemented with virginiamycin generated a better weight gain and FCR compared to the control group (P<0.01 and P<0.05 respectively). No improvement was found in weight gain or the feed conversion ratio by increasing the levels of virginiamycin. Groups supplemented with oxytetracycline gave the same results as the control group, both in weight gain and FCR. All levels of oxytetracycline had a lower weight gain compared to virginiamycin at the 20 and 40 mg/kg feed, but did not differ from virginiamycin at 10 mg/kg feed. All levels of oxytetracycline and virginiamycin showed no significant difference in FCR but virginiamycin seems to give a better result. For carcass evaluation, no significant differences were found in dressing and fat percentages though the antibiotic groups tended to give a higher fat percentage. No residues of oxytetracycline was detected either before or after the withdrawal period of 7 days. For virginiamycin, a result could not be determined because the minimum detectable level of the virginiamycin test being used was higher than 0.1 ppm. Further studies with new analytical techniques showing less than 0.1 ppm detectable levels should be conducted for checking virginiamycin residues, in order to check on any possible health hazard to consumers.