Caecal microflora and fermentation pattern in exclusively milk-fed young rabbits

Thirty two 22- to 42-day-old SPF New Zealand White rabbits of both sexes were used and sequentially slaughtered, 8 per day, at 22, 29, 35 and 42 days of age. Data were treated by variance analysis. Rabbits given only a milky diet up to 42 days of age exhibited a caecal fermentation pattern turned towards a proteolytic metabolic activity (high levels in NH3 and in branched-chain fatty acids and valeric acid: 17 mmol/l and 1 mmol/l, on average, respectively). The absence of cellulolytic microflora and the low concentration of the total volatile fatty acids (tVFA) could be explained by the lack of substrate that would have been brought by a solid feed. From day 29 onwards, the low tVFA (12.5 mmol/l) and high NH3 concentrations (16.5 mmol/l) explained the high pH value (6.8 on average). This may be considered as a pathological value for weaned rabbit but in our case no clinical sign of diarrhoea was observed. The evolution of the colibacilli flora according to age was similar to that usually described and thus was not correlated with pH, tVFA or cellulolytic flora. The evolution of the colibacilli population (from 10(7) bact/g on day 22 to 10(3) on day 42) seemed dependant on ontogenic factors rather than on nutritional ones.