The utilization of untreated and calcium hydroxide treated wheat straw by sheep

Abstract

The intake, digestion and utilization of diets comprising milled untreated or calcium hydroxide treated wheat straw (909 g kg −1), molasses (55 g kg −1), urea (18 g kg −1) and minerals (18 g kg −1) offered ad libitum, were compared. In addition, the treated straw-based diet was given at 75 and 50% of voluntary intake. The intake, excretion and apparent retention of sulphur, calcium and phosphorus were measured for the four treatments. When fed ad libitum, sheep consumed more organic matter from the treated straw diet than from the untreated straw diet (685 vs. 398 g/day) and digested more of the organic matter (62 vs. 54%) and neutral detergent fibre (63 vs. 53%). Restricting the intake of the treated diet increased digestibility by 2 percentage units. There did not appear to be any adverse effect from feeding with the treated straw diets and most of the additional calcium was excreted in faeces. All sheep were in negative calcium balance (−0.37 to −0.58 g/day), were around zero balance for phosphorus (−0.11 to 0.08 g/day) and retained small amounts of sulphur (0.01–0.16 g/day) owing to sulphur incorporation into wool. Treatment of wheat straw by soaking in Ca(OH) 2 can increase intake and digestibility of the straw, thus reducing the rate of liveweight loss by sheep fed on diets containing in excess of 90% straw.