Effects of treatment of barley straw with anhydrous ammonia and supplementation with heat-treated protein meals on feed intake and liveweight performance of growing lambs

Abstract

Two feeding experiments were conducted in which lambs were given a basal diet of barley straw, supplemented with urea and minerals. The aim of the experiments was to increase lamb performance by (i) supplementation of the diet with protein meals that were largely undegraded in the rumen, (ii) treating the barley straw with anhydrous ammonia to increase its digestibility, or (iii) a combination of both. In Experiment 1, lambs were given the basal diet supplemented with 0, 60, 120, 180, 240, 300 or 360 g heat-treated protein-meal/kg straw. At the 300 g/kg level of supplementation, the protein pellet increased liveweight gain by 82 g/day, intake of barley straw by 110 g/day, and wool growth by 3.3 g/day, in comparison with unsupplemented lambs. In Experiment 2, untreated barley-straw or barley straw treated with anhydrous ammonia (4% w/w) was given to growing lambs. Each diet was supplemented (g/kg straw diet) with 100, 200 or 300 of two heat-treated protein-meals. Ammoniation of the barley straw increased dry matter (DM) digestibility in vitro from 49 to 57%, and hemicellulose content was reduced by 20%. Total N content of the straw was increased from 4.6 to 9.8 gN/kg DM by ammoniation, 65% of the increased N being potentially degradable in the rumen. As a result of ammoniation, digestible dry-matter intake of lambs was increased by 60 g DM/day and liveweight gain increased by 15 g/day. There was no significant difference between the two protein supplements with respect to either total feed intake or liveweight gain. Liveweight gain was significantly increased by both supplements (71, 106 and 125 g/day for each level of supplementation, respectively), but neither supplement had a significant effect on the intake of barley straw. Supplementation of a low-protein, low digestible diet of barley straw with a pelleted protein-meal considerably increased liveweight gain of growing lambs and maintained straw intake. By comparison, treatment of barley straw with anhydrous ammonia increased its digestibility, but had only a minor effect on lamb performance.