Utilization of clover diets by sheep. 1. Intake and digestion of organic matter and cell wall constituents

Abstract

Nine mature Merino sheep received three clover diets in a randomized block design experiment. The diets were mature subterranean clover (MSC), apparent organic matter digestibility (OMD) 60%; green subterranean clover (GSC), OMD 72%; persian clover (PC), OMD 67070, and were given at 95% of measured ad libitum intake. The voluntary consumption of the MSC was lower than the intakes of the CSC and PC. Consequently, the sheep given MSC lost weight, while those receiving the more digestible diets gained weight. Associated with the different intakes in these clover diets, there there were no differences in the levels of ruminal fill, but there were differences in ruminal loads of dry matter (DM) and neutral detergent fibre (NDF) in sheep given MSC, GSC and PC, respectively. The flows of DM and OM through the abomasum were lower for MSC, and with a tendency for the fractional outflow rate of NDF of this diet to be lower (2.3 v. 2.8% h-1) when compared to the GSC and PC hays. The proportions of apparent OM (0.65-0.71), of NDF (0.71-0.82) and of ADF (0.95-140) digestion occurring in the rumen were similar for the three clover hays. The fractional digestion rates of potentially digestible NDF were higher for the more digestible clovers (c. 8.6% h-1) than for the MSC (6.5% h-1). The intake of the higher digestibility clovers may have been more related to the capacity of the sheep to use absorbed nutrients than to constraints imposed by ruminal digesta load, rate of digestion in the rumen or rate of outflow to the omasum. With the MSC the level of ruminal or dry matter load was low. In addition, the fractional rates of digestion and of outflow of cell wall constituents were or tended to be lower for this diet than for the other clovers. Intake of MSC may have been limited not only by these factors, but also by the supply of essential nutrients to the tissues or by other characteristics of the hay influencing its acceptability to sheep.