The relationship between feeding level, rumen particulate and fluid turnover rate and the digestibility of soya hulls in cattle and sheep (including a comparison of Cr-mordanted soya hulls and Cr 2O 3 as particulate markers in cattle)

Abstract

The aim of this work was to investigate the inter-relationships between feeding level, digestibility and rumen particulate and fluid turnover rate (k1p and k1f: % per hour) for high concentrate diets in cattle and sheep. In Experiment 1, four fistulated steers were used in a 4×4 Latin square experiment to determine k1p at high (12.45 kg/d) and low (6.48 kg/d) intakes using either Cr-mordanted soya hulls or Cr 2O 3 as particulate markers. In the second and last period of this experiment, soya hulls digestibility and k1f were determined for each intake level. In Experiment 2, seven 1 year old wether sheep were used to determine the digestibility of soya hulls, k1p and k1f at high (907 g/d; n=3) and low (703 g/d; n=4) intakes. Increasing feeding level depressed DM, OM and GE digestibility ( P<0.05) as well as DM and NDF in-sacco degradability ( P<0.10) for cattle. Depressions similar in magnitude were realised for sheep in DM, OM, CP, NDF, ADF and GE digestibility ( P<0.10). For cattle and sheep, the effect of increasing feeding level on k1p approached significance ( P<0.10). However, no effect of feeding level was observed on k1f in cattle or sheep ( P>0.10). For the pooled data set, linear relationships ( P<0.05) were found between k1p and DM, OM, CP, NDF and GE digestibility. There was no effect of marker type on k1p determined using cattle ( P>0.05). These results indicate that depressions in digestibility at high feeding levels are associated with higher rumen turnover rates and that much of the variation in concentrate digestibility can be explained by changes in rumen turnover rate in both species.