Age dependent variation of caecal contents composition of young rabbits

In order to study the age dependent variation of caecal contents composition, a young rabbit was slaughtered out of 6 conventional litters at the age of 22; 25; 28; 32; 36; 42 and 56 days. Rabbits were fed a standard diet before and after weaning (at 28 days of age). Daily growth and caecum size were determined. Caecal contents were analyzed for dry matter (DM), pH, crude protein (CP), neutral detergent fibre (NDF), ribonucleic acid (RNA), lactate, ammonia nitrogen and volatile fatty acids (VFA). Between 22 and 25 days of age, a highly significant drop in CP content was found, associated with an increase in NDF content. RNA values tended to decrease with age, but it is striking that the RNA/CP ratio suggests that about 50% of CP is microbial N, very early in the development (22 days). No significant changes of ammonia nitrogen concentration with age were observed, and lactic acid concentration showed some significant changes, suggestive of a decrease after weaning. Total VFA concentration is suggestive of a progressive and significant (P < 0.01) increase reaching a plateau after 42 days (83.7 mmoles/kg). Molar proportions of propionate and butyrate varied significantly (P < 0.001) and inversely with age. Propionate drops by nearly 50% while butyrate proportion doubles between 22 and 56 days of age. The shift from a propionic to a butyric pattern occurs already at day 25. Correlation analysis revealed significant associations between CP-NDF and RNA. The significant negative correlation between pH and daily weight gain reflects the relation caecal pH-animal health. PH was correlated with lactate and VFA concentration.