Digestion by sheep of ground and unground dried molassed sugarbeet pulp diets and the effect of partially replacing the beet pulp with barley

Abstract

SUMMARYA 4 x 4 Latin square design experiment was performed at the Ruminant Research Centre, Cockle Park Farm, University of Newcastle upon Tyne, in 1986 to determine the effect of grinding molassed sugarbeet pulp (MSBP) to varying degrees of fineness on overall apparent digestibility in wether sheep when the product constituted 90% of dry matter intake. A product (designatedS) consisting of the pelleted screenings of unground MSBP was significantly less digestible than the other three products. No significant difference in overall apparent digestibility was observed between unground, coarsely ground and finely ground MSBP prepared from the same batch.In a 4 x 6 randomized block design experiment, mature wethers equipped with rumen, duodenal and ileal cannulae were fed, in two meals, 1000 g concentrates and 100 g chopped hay per day. The concentrates consisted of 820 g mixture of barley and MSBP, 167·5 g soyabean meal, 10 g vitamins and minerals and 2·5 g chromic oxide per kg (fresh weight). The ratio of MSBP: barley was 1:3, 1:1 or 3:1 and the MSBP was either unground or finely ground. The aim was to determine the effect of replacing MSBP with barley on the nature of the rumen fermentation, overall apparent digestibility of the diet and the efficiency of rumen microbial protein synthesis (using 35S as a microbial marker).There were no significant differences between the six diets in overall apparent digestibility of dry matter and organic matter, but N digestibility increased significantly (P > 0·05) as barley replaced MSBP in the diet. As before, the particle size of MSBP had no effect on overall apparent digestibility of the diet. The quantity of microbial N was reduced (nonsignificantly) and the efficiency of rumen microbial protein synthesis decreased (P> 0·05) compared with the other treatments when sheep were fed diets in which the ratio of MSBP: barley was 1:1. The particle size of MSBP had no effect on these factors.As barley replaced MSBP in the diet, the mean pH of rumen fluid, calculated over 24 h, tended to decrease and there was a significant increase (P> 0·05) in the length of time that the rumen fluid was below pH 6. There were no significant differences between treatments in the concentration of ammonia-N in the rumen fluid. The dilution rate of rumen fluid (measured using14C-Cr EDTA and Co EDTA as markers) decreased (P> 0·05) when MSBP replaced barley in the diet, and ground MSBP gave rise to lower (P> 0·05) dilution rates than unground MSBP. There were no significant differences between treatments in the ruminal concentration of total volatile fatty acids (VFAs) or the proportions of individual VFAs.