Comparison of rumen fermentation patterns and in situ degradation of grazed herbage in Churra and Merino sheep

The aim of this experiment was to study the effect of breed (Churra and Mer ino) and advancing season (middle June, late July and early October) on rum en fermentation in sheep grazing a continuously stocked grass/white clover pasture. Six mature sheep (three Churra and three Merino) fitted with rumen cannulae were used. During each grazing period, samples of the grazed herb age (obtained using three oesophageal-cannulated sheep from each breed) and grass hay were incubated in situ. Rumen pH, ammonia-N and volatile fatty a cids concentrations were determined in ruminal samples at 11.00, 14.00, 17. 00 and 21.00 h. Breed did not affect (P > 0.05) any of the dry matter (DM) degradation parameters of grazed herbage during July, but potential DM degr adability and effective DM degradability were higher (P < 0.05) in Merinos than in Churras during June and lower (P < 0.05) during October. On the con trary, there were no differences (P > 0.05) between breeds in the effective degradability of either DM or neutral-detergent fibre from grass hay. Diff erences between breeds in rumen degradation parameters of grazed herbage ar e discussed in relation to seasonal changes in the composition of the graze d herbage and to changes in rumen parameters in both breeds. (C) 2000 Elsev ier Science B.V. All rights reserved.