[Effect of the addition of a fiber-rich concentrate to a hay-based diet, offered at 2 dietary levels to adult rabbits. 1. Mean retention time of digesta].

The influence of adding a fibre rich concentrate feed (wheat bran or beet pulp) to a hay-based diet (orchard grass-lucerne mixture; 50/50) upon the rate of passage of digesta of these two fractions (hay and concentrate) was measured in three groups of 8 adult doe rabbits (White New Zealand x California). The three diets composed of either 90% hay, or hay + bran or hay + pulp were offered at two levels of feeding, i.e. ad libitum and 2/3 ad libitum. The retention time of the two main fractions was measured by means of two tracers, i.e. ytterbium-169 bound to hay and cerium-141 to bran or pulp. Animals fed on the 90% hay diet excreted more than 90% of the tracer during the first 24 h. The mean retention time (MRT) of this diet was the shortest (on an average 14.8 h). The addition of pulp or bran increased the MRT of the diet by 2 and 4 h, respectively. Feed restriction led to a 5 to 7 h earlier period of caecotrophy with a subsequent lengthening of the MRT by 2 to 4 h according to groups. The two hay + "concentrate" diets gave almost the same 169Yb and 141Ce excretion curves. Thus, the mean retention time seems to be the same for digesta from hay and "concentrate" (non significant deviations).