Challenging the growing rabbit with a moderately pathogenic E. coli under ad libitum or limited feed intake conditions: impact on digestive physiology, bacterial communities, and on post-weaning growth

The impact of a challenge with moderately pathogenic Escherichia coli O128:C6 on the digestive physiology and gut bacterial community of growing rabbits under two feeding programmes was analysed. Upon weaning (28 d old), 180 rabbits were allocated to four groups (9 cages of 5 rabbits per group) for two weeks: group C100 was non-inoculated and fed ad libitum ; C70 was non-inoculated and feed intake was limited to 70% of C100; I100 and I70 were inoculated and fed ad libitum or restricted to 70%, respectively. At the age of 31 d (D0), rabbits were orally inoculated with E. coli (2.2×108 colony forming units/rabbit). The effects of inoculation spiked on D4, with a 28% lower growth rate for I100 than for C100. Limited feed intake reinforced the inoculation’s effects on growth: I70 had a 66% lower growth rate than C70. The morbidity rate peaked at 42% between D4 and D7 for inoculated groups, without significant effect of the feed intake level.  E. coli concentration peaked on D5/D6 in the caecum of the I100 and I70 groups. Inoculation reduced by 30% ( P <0.05) the villus height/crypt depth and villus/crypt area ratios in the ileum, with no significant effect of the intake level. Inoculation was associated with a tenfold increase in serum haptoglobin ( P <0.001) for both ad libitum and restricted rabbits. On D5, the inoculation modified the structure of the ileal bacterial community ( P <0.05), but not that of the caecum. The feed intake level did not affect either the structure or diversity of the bacterial community, both in the ileum and caecum.