Effects of level of intake and of available volatile fatty acids on the absorptive capacity of sheep rumen

The objective of this experiment was to determine the respective effects of level of intake and of the amount of volatile fatty acids (VFAs) present in the rumen on VFA ruminal absorption. In a factorial design, six ewes received a hay diet either at 126 or at 73% of energy maintenance requirements. Their capacity of absorption of VFAs was evaluated by the method of temporarily isolated rumens, in which the rumen was filled with solutions containing high or low amounts of VFAs. Rate of absorption (amount of VFAs absorbed per hour) was significantly higher, by 32% on average, in sheep fed the high intake than in sheep fed at low intake. The proportion of initial VFAs absorbed did not depend on the concentration of VFAs introduced in the rumen, so that the amount of VFAs absorbed varied as the concentration of VFAs introduced in the rumen. The decrease in intake resulted in a decrease by 32% in the rate of absorption of total VFAs. No interaction between concentration of VFAs and previous intake was observed. This suggests that the capacity of the rumen to absorb VFAs is reduced at low intake even if low amounts of VFAs are available.