Effect of the dietary fibre origin on the digestion and on the caecal fermentation pattern of the growing rabbit

Abstract

AbstractThe effect of the origin of dietary fibre on digestion and caecal fermentation in the rabbit was studied independently of variations in the level of the different cell wall constituents (cellulose, lignin, etc.). Relationships between microbial activity and the digestion of nutrients were also evaluated over a 4-week growth period. Three experimental diets were givenad libitumfrom, weaning (28 days) to three groups of nine New Zealand White rabbits, subjected to caecal cannulation at 35 days of age with in-vivo digesta sampling at 6, 7, 8, 9 weeks of age. The diets were similar in their content of neutral-detergent fibre (NDF) (320 g/kg dry matter) and in the respective proportions of cell wall constituents (hemicelluloses (NDF - acid-detergent fibre (ADF)) = 0·54, cellulose (ADF -acid-detergent lignin (ADL)) = 0·37, lignin (ADL) = 0·09), but they differed by their main fibre origin: lucerne meal = diet LM, sunflower meal = diet SM, wheat straw = diet WS.As a consequence of the similar fibre level, the dietary intake was similar among the diets. The NDF digestibility ivas 0·03 units lower for the diet SM, and led to a lower quantity of NDF degraded (3·7 g NDF per day per kg live weight) compared with LM and WS groups (5·0 g NDF per day per kg live weight). Significant variations in caecal volatile fatty acid (VFA) levels were observed between LM and WS, although the intake of nutrients was rather similar, therefore suggesting a direct effect of the botanical origin of fibre. Compared with LM and SM diets, a significantly lower caecal VFA level was found for the WS diet and was associated with a higher incidence of digestive disorders. In the WS diet, fibres that come from only one botanical origin (wheat straw and bran) may be unfavourable to caecal fermentation and to the health status. The ammonia level, the caecal pH and the proportions of the different VFAs were not affected by the diets.The total VFA level showed a significant quadratic trend between 6 and 9 weeks of age, whereas the butyrate molar proportion showed a significant linear increase from 0·08 to almost 0·10. In parallel, the daily quantity of hemicellulose digested was positively correlated to the butyrate molar proportion (r = 0·884,P< 0·001), and negatively correlated to the caecal pH (r = -0·705, P = 0·022).