The aim of this study was to determine the effect of the live yeast Saccharomyces cerevisiae on the growth performance, caecal ecosystem and overall health of growing rabbits. A control diet was formulated (crude protein: 15.9%; neutral detergent fibre: 31.6%) and another diet obtained by supplementing the control diet with 1 g of Saccharomyces cerevisiae (6.5×10 9 colony-forming units) per kg of diet. Ninety 35-d old rabbits were allotted into 3 groups: TT (rabbits offered the supplemented diet from 17 d of age onwards), CT (rabbits offered supplemented diet from 35 d) and CC (rabbits fed non-supplemented diet). Body weight (BW) and feed intake were measured weekly and mortality was controlled daily. At 35, 42 and 77 d of age, 6 rabbits from each group were slaughtered and digestive physiological traits, serum clinical chemistry parameters, fermentation traits, and the composition of caecal microbiota examined. At 42 and 56 d of age, 10 rabbits from each group were injected intraperitoneally with 100 µg/animal of ovalbumin and blood samples were collected for examination of plasma immunological parameters. Throughout the experiment (5-11 wk), weight gain and feed intake (37.8 and 112.6 g/d, on av.) were not affected by yeast, except for weight gain in the first week after weaning, which was the highest in TT animals among the 3 groups (48.1 vs. 43.9 and 44.2 g/d for TT, CC and CT, respectively; P=0.012). This may be due to the increased trend in feed intake (P=0.072) in the TT group (96.4 g/d) compared to the others. Mortality (5/90) was low and did not differ among the 3 groups. Treatments had no effect on slaughter traits at the 3 sampling dates (35, 42 and 77 d). Only the weight of the empty caecum (% BW) was higher (P=0.02) in CC (2.2%) and CT (2.3%) than in TT group (1.8%) at 77 d of age. Treatments did not overtly affect the caecal microbiota, although the number of total anaerobic bacteria and Bacteroides were lower (10 8 and 10 7 /g caecal digesta, respectively) in rabbits from CC group compared to those of CT and TT groups at 42 d of age (P=0.03). No difference between groups was observed for caecal short chain fatty acids profile, blood traits, or IgG and cytokine profile. In conclusion, supplementation of feed with yeast did not modify growth traits and resulted in only a temporary increase in weight gain and a slightly altered caecal microbiota after weaning.

A study was conducted to determine the effect of live yeast supplementation in the diet of rabbit does on their mortality and reproductive performance and the performance of their progeny. A total of 52 cross-bred rabbit does (New Zealand×Californian) were divided into 2 groups differing in diet offered during 2 reproductive cycles and containing (group S; n=26) or not (group C; n=26) 1 g of yeast (Actisaf Sc 47, S.I. LESAFFRE, France)/kg of feed. Natural mating was performed 11 d after kindling and kits were weaned at 28 d of age. Body weight of litters was measured at birth, 21 d and at 28 d of age (weaning). Mortality of kits and rabbit does was monitored daily, and fertility of rabbit does and viability rate of kits at birth were also determined. Weight and litter size at birth and at weaning, litter weight gain during lactation and length of gestation were similar between the 2 groups during the 2 cycles. The mortality of does during the experiment was higher in group C than in group S (27 vs. 4%; P<0.05). Fertility rate of rabbits does and viability rate of kits at birth were higher (P<0.05) in rabbits fed with the supplemented diet than those with the control diet during the second lactation. In the first cycle, kit mortality was lower in S group (15.5%) than the C group (24.7%) during the first 21 d (P<0.05). However, no difference was observed during the second lactation. In conclusion, our results suggest that the inclusion of yeast in the diet of rabbit does could trigger positive effects on the fertility and mortality of rabbit does, as well as on the viability rate of kits at birth.