Effect of diet supplementation with Toyocerin (Bacillus cereus var. toyoi) on performance and health of growing rabbits

Two trials were performed to evaluate the effect of a dietary supplementation with Bacillus cereus var. toyoi on performance and health of growing rabbits. The studies were conducted in two commercial farms using the same experimental diets. In the first trial, 216 rabbits were controlled from 35 d (weaning) until 70 d of age. In the second trial, 180 rabbits were controlled from 37 until 79 d of age. At weaning, rabbits were put into bicellular cages, divided into three groups and fed the experimental diets: diet C, diet T1 and diet T2 supplemented with 0, 200 ppm (2x105 spores/g diet) and 1000 ppm (1x106 spores/g diet) of Toyocerin® (concentration: 1x109 B. cereus var. toyoi spores/g), respectively. The diets did not contain antibiotics or growth promoters and presented similar chemical composition (CP: 17.4% DM, NDF: 40.8% DM; ADL: 5.2% DM, starch: 16.5% DM). The differences in growth performance between the two trials depended mainly on the different final age of rabbits. Weight gain (42.0 vs 36.5 g/d) was lower and feed conversion (3.12 vs 3.96) higher in the second trial. Mortality (13.0% vs 21.7%) and morbidity (2.8% vs 25.0%) were significantly higher in the second trial. The probiotic supplementation (diet C vs diets T1+T2) significantly increased final live weight (2,517 vs 2,580 g; P=0.02) and daily weight gain (38.2 vs 39.8 g/d; P=0.01) and improved feed conversion (3.63 vs 3.50; P=0.01). Morbidity was significantly lower with supplemented diets (18.2 vs 10.3%; P=0.03), while mortality and sanitary risk were not affected by dietary treatment. No effect of probiotic inclusion rate (diet T1 vs diet T2) and no significant interaction between dietary treatment and trial were measured. In conclusion, the supplementation of Bacillus cereus var. toyoi improved growth performance and reduced morbidity of rabbits reared in farms with or without severe health problems. Increasing probiotic inclusion rate from 2x105 to 1x106 spores/g diet did not improve rabbit growth performance and health.