Digestible fibre to starch ratio and antibiotic treatment time in growing rabbits affected by epizootic rabbit enteropathy

The study aimed to evaluate if the digestible fibre (DF, hemicelluloses+pectins) to starch ratio of the diet and the time of antibiotic treatment after epizootic rabbit enteropathy (ERE) outbreak affect health status, digestive physiology, growth performance, and carcass traits of early weaned rabbits. Two hundred forty Grimaud hybrid rabbits were put in individual cages and controlled from 25 d of age to slaughter (70 d). The rabbits were assigned to four groups according to a 2x2 factorial arrangement (2 DF to starch ratios by 2 antibiotic treatment times). Half of the rabbits fed ad libitum diet L, with low (1.0) DF to starch ratio (19.1% DF and 18.9% starch as-fed) and half fed diet H with high (2.5) DF to starch ratio (23.9% DF and 9.6% starch). The diets were characterized by similar protein (16.8%), ADF (19.8%), and ADL (3.9%) concentrations. After the ERE appearance, half of the rabbits within diet were submitted to an early antibiotic treatment (from 38 to 42 d of age), while half of the rabbits to a late treatment (from 45 to 49 d). The antibiotic treatment was realized by an association of oxytetracycline hydrochloride (100 g/100 l) and colistin (24 g/100 l) administered in water. At 43 d of age, 36 rabbits (6 per group) were sacrificed to collect caecal content and ileum mucosa samples. Increasing DF to starch ratio of the diet improved fibre fraction digestibility (P<0.001) therefore maintaining a similar nutritive value (digestible energy=10.7 MJ/kg) among diets. Mortality (31.7% vs. 11.5%) and morbidity (38.5% vs. 18.5%) significantly decreased (P<0.001) by increasing DF to starch ratio, thus reducing sanitary risk by two thirds. These results were apparently associated to a higher caecal fermentation activity (volatile fatty acids: 49.6 vs. 60.7 mmol/l; P=0.03) in rabbits fed the high DF to starch diet, while ileal mucosa morphometry was unaffected. Once the health status was recovered, growth performance and slaughter results were scarcely affected by the dietary treatments. An early antibiotic treatment, administered within one week from the first ERE symptoms, reduced mortality (17.3 vs. 26.0%; P=0.07) and improved growth performance and slaughter results in comparison with a later treatment. Even the early antibiotherapy did not avoid that rabbit mortality reached a level unacceptable for a commercial farm, however. The association of a diet with a high DF to starch ratio and an early antibiotic treatment permitted to maintain the mortality at a basic level (5.8%) and provided the best growth performance and carcass quality.