Divergent selection for digestive disorders in two commercial rabbit lines : response of crossbred young rabbits to an experimental inoculation of Echerichia coli 0103.
Résumé
A divergent selection for digestive disorders, R for resistance and S for sensitivity, based on routine observational data of signs of enteropathy, was carried out in AGP39 and AGP59 commercial lines of the Hypharm breeding company. Two successive batches (B1 and B2) of 178 crossbred animals, 89 R and 89 S, were produced by mating AGP39 well evaluated bucks with AGP59 well evaluated does and AGP39 bad evaluated bucks with AGP59 bad evaluated does, respectively. In each batch, 27 R animals (RC) and 27 animals (SC) were chosen to constitute the control group while 62 R animals (RI) and 62 S animals (SI) were chosen for inoculation. Individual EBV of animals of the RI group and of the SI group was calculated as the mean of their sire and dam’s EBV. In each batch, 31 animals with the lowest EBV in the RI group and 31 animals with the highest EBV in the SI group were sorted to constitute the group RRI and the group SSI, respectively.Young rabbits were carried from Hypharm to the INRA Experimental Platform for Infectious Disease (PFIE) just after weaning at 30 days of age. Inoculated rabbits received 105 bacteria of the strain LY265, E. Coli O103:H2:K-, rhamnose negative (Licois et al., 1992), by oral administration, at 37 days of age. All animals were weighed and checked for clinical symptoms just before the inoculation, 2 days, 6 days, 9 days and 13 days after the inoculation. Average daily weight gain was calculated for each interval. Individual mortality was recorded daily. 13 days after inoculation, 9 rabbits of each sub-group were sacrificed to measure pH of the caecal digesta and for caecum and caecum appendix weighing. The impact of the E. coli challenge was significant for growth and for the caecum relative weight. Although mortality tended to be higher in sensitive animals than in resistant animals in batch 1 (p=0.12) there was no significant difference between RI and SI groups for cumulative mortality, daily weight gain and caecum measurements. Mortality was significantly lower (p=0.04) in RRI group than in SSI group at day 11, day 12 and day 13 (31.8 %, 34,8 % and 36.6 % vs. 50 %, 5.1 % and 54.7 % respectively). This difference corresponded to 11 animals for each of the 3 periods.
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