Seasonal effect on rumen function in sheep on range in the Accra Plains of Ghana.

This study aimed at investigating the effect of the seasonal decline in quality and availability of feed on rumen function in sheep grazing without supplementation. Effects of season on rumen pH, ammonia nitrogen concentration and rumen degradation of urea-treated rice straw in grazing sheep were determined. Four fistulated Djallonké sheep were added to a group of grazing sheep and used for this study. Rumen contents were sampled for pH and ammonia in the rainy season and in the dry season. Ammoniated rice straw was incubated in the rumen to determine its degradation characteristics. Rumen pH was higher (p < 0.1) in the dry season than in the rainy season. Rumen ammonia nitrogen concentrations on the other hand were similar (p > 0.05) in the two seasons. In sacco dry matter degradation parameters of urea-ammoniated rice straw showed seasonal differences in the soluble (a) and the insoluble but degradable (b) fractions as well as lag time before the start of degradation. It was concluded that despite higher pH in the dry season and similar ammonia nitrogen concentration in the two seasons, rumen degradability of dry matter of urea-treated rice straw in sheep was higher in the rainy season than that in the dry season.