IN-VIVO STUDY OF CIRCADIAN VARIATIONS OF THE CECAL FERMENTATION PATTERN IN POSTWEANED AND ADULT-RABBITS

Two groups of cecal cannulated rabbits (postweaned and adult, 6 and 16 wk of age, respectively) were used to compare the circadian variation s of the fermentation pattern. Rabbits were kept in metabolism cages u nder a 12:12 light-dark schedule (0700 to 1900). For each rabbit, a to tal of 12 samples of cecal material were collected (every 12 h) for si x consecutive days to cover a 24-h cycle; feed ingestion and hard fece s elimination were recorded. For postweaned and adult rabbits, the per iod of cecotrophy practice was mainly 0400 to 1200, and also 2200 to 2 400 for the former and 0800 to 1400 for the later. Compared with those of adult rabbits, the cecal contents of the postweaned rabbits were c haracterized by a lower DM level (17.6 vs 20.3%; P < .001), a lower VF A level (65.4 vs 86.1 mM; P < .001), and a higher ammonia N level (7.6 vs 6.1%; P = .02) related to the presence of a double period of cecot rophy (only one in the adult rabbits), and corresponding to the postwe aning adaptation of the cecal microflora to a dry feed. A lower butyra te molar proportion was found in postweaned than in adult rabbits (10. 5 vs 13.6%; P = .004), whereas molar proportion of acetate and propion ate remained similar regardless of the age of the rabbit. In the postw eaned rabbits, changes in fermentation pattern were related to circadi an rhythm of the cecotrophy practice. During this period, the levels o f total VFA, acetate, and butyrate progressively decreased; the minimu m was reached at 1200 (e.g., 53.8 44.6, and 4.4 mM, respectively); the corresponding propionate:butyrate ratio was 1.0.