Digestive effects of fibre and starch intake in the growing rabbit

Abstract

Rabbits can efficiently utilise low-fibre diets containing high contents of digestible energy. Lowering the dietary fibre level, generally associated with an increased starch level, leads to an increased incidence of digestive disturbances, which are frequently lethal for growing rabbits. Dietary fibre and starch levels must then be controlled to allow for both optimal growth rates and feed security. An increase in lignocellulose (ADF, slightly degraded) reduces the feed digestibility and stimulates the digesta rate of passage, without greatly affecting the caecal fermentations. An increase in more easily digestible fibre (hemicellulose + pectins) slightly affects the feed digestibility, but does not slow the rate of passage; on the other hand it promotes caecal microbial activity (CMA). An ADF increase seems efficient in reducing the incidence of digestive troubles and mortality during the fattening period.

The CMA can also be affected by the quantity of starch entering the caecum, itself dependent on the nature of the starch and the age of the animal. Increasing the dietary starch level could promote digestive troubles, even when ADF level is in agreement with current recommendations. Thus, the "security level" of a feed can not only be defined by a minimum level of ADF, but must also take into account a maximum level of starch. The replacement of starch by easily digestible cell-wall constituents, in a diet having a minimum level of lignocellulose, could be a solution to the antagonism between efficiency and feed security in the growing rabbit.