RELATIONSHIPS BETWEEN MICROFLORA AND CECAL FERMENTATION IN RABBITS BEFORE AND AFTER WEANING

Some microbiological and biochemical parameters of caecal content were studied in 15- to 49-d-old rabbits that were slaughtered sequentially . The ammonia level did not differ before weaning (11.5 mmol/L on aver age) (P = 0.41) or after weaning (7.4 mmol/L on average) (P = 0.19) bu t decreased by 40% (P < 0.001) between days 29 and 32. The level of pH decreased linearly (Pi 0.001)throughout the period studied. The Esche richia coli counts decreased up to weaning (P < 0.001) and was then no t significantly affected by age (P = 0.12). The total volatile fatty a cid (VFA) concentration increased between days 15 (8.2 mmol/L) and 25 (33.9 mmol/L) (P < 0.05) and then levelled off below 40 mmol/L. Molar proportions in propionate and in branched-chain fatty acid (BCFA) and valeric acid were high at day 15 but decreased when the animals began to eat solid feed. The C3/C4 ratio reversed at weaning (3.8 on day 15 and 0.5 on day 49) whereas the acetic acid proportion was not affected by age (P = 0.19). High counts of anaerobic microflora were found bet ween 15 and 22 d of age (10(11) bacteria/g of caecal content, on avera ge) and did not change significantly according to the age (at about 10 (10) bacteria/g), from day 29 until the end of the experiment (P = 0.2 9). Amylolytic flora had a similar evolution at a slightly lower level . In contrast, under our breeding conditions cellulolytic microflora s lowly colonized the caecum and remained at a low level. The discrimina nt analysis revealed relationships between ages, intestinal microflora and fermentation parameter; the colibacilli flora was associated with mother-fed animals and amylolytic flora which was linked to BCFA and valeric acid, while the cellulolytic flora was associated with animals older than 4 weeks and linked to the production of C2, C3, C4 and amm onia.