In vivo study of circadian variations of the cecal fermentation pattern in postweaned and adult rabbits.

Abstract

Two groups of cecal cannulated rabbits (postweaned and adult, 6 and 16 wk of age, respectively) were used to compare the circadian variations of the fermentation pattern. Rabbits were kept in metabolism cages under a 12:12 light-dark schedule (0700 to 1900). For each rabbit, a total of 12 samples of cecal material were collected (every 12 h) for six consecutive days to cover a 24-h cycle; feed ingestion and hard feces elimination were recorded. For postweaned and adult rabbits, the period of cecotrophy practice was mainly 0400 to 1200, and also 2200 to 2400 for the former and 0800 to 1400 for the later. Compared with those of adult rabbits, the cecal contents of the postweaned rabbits were characterized by a lower DM level (17.6 vs 20.3%; P < .001), a lower VFA 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 cecotrophy (only one in the adult rabbits), and corresponding to the postweaning adaptation of the cecal microflora to a dry feed. A lower butyrate molar proportion was found in postweaned than in adult rabbits (10.5 vs 13.6%; P = .004), whereas molar proportion of acetate and propionate remained similar regardless of the age of the rabbit. In the postweaned rabbits, changes in fermentation pattern were related to circadian rhythm of the cecotrophy practice. During this period, the levels of total VFA, acetate, and butyrate progressively decreased; the minimum was reached at 1200 (e.g., 53.8 44.6, and 4.4 mM, respectively); the corresponding propionate:butyrate ratio was 1.0.