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 Cr2O3 as particulate markers incattle)

The aim of this work was to investigate the inter-relationships between fee ding level, digestibility and rumen particulate and fluid turnover rate (k1 p and k1f: % per hour) for high concentrate diets in cattle and sheep. In E xperiment 1, four fistulated steers were used in a 4 X 4 Latin square exper iment to determine k1p at high (12.45 kg/d) and low (6.48 kg/d) intakes usi ng either Cr-mordanted soya hulls or Cr2O3 as particulate markers. In the s econd and last period of this experiment, soya hulls digestibility and k1f were determined for each intake level. In Experiment 2, seven 1 year old we ther 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 f eeding 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 digesti bility (P < 0.10). For cattle and sheep, the effect of increasing feeding l evel on kip approached significance (P < 0.10). However, no effect of feedi ng 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 d etermined using cattle (P > 0.05). These results indicate that depressions in digestibility at high feeding levels are associated with higher rumen tu rnover rates and that much of the variation in concentrate digestibility ca n be explained by changes in rumen turnover rate in both species. (C) 2001 Elsevier Science B.V. All r ights reserved.