The potential of sulla in pasture-based systems

Abstract

A feed evaluation trial compared lamb growth, rumen function and protein synthesis from either pasture (perennial ryegrass (Lolium perenne)/white clover (Trifolium repens)-dominant), lucerne (Medicago sativa), sulla (Hedysarum coronarium, which contains condensed tannins (CT)) or a lucerne:sulla mixture. The 8 week trial involved 32 weaned ram lambs allocated to either pasture (80% ryegrass and 20% white clover), lucerne, sulla, or a 50:50 lucerne:sulla mixture (DM basis; 8 per diet). Measurements included feed intake, liveweight (LW) gain, rumen ammonia (NH₃) and volatile fatty acid (VFA) concentrations. A sub-group of 16 lambs (4 from each treatment) were given a continuous infusion of ³⁵S-cysteine and ³⁵S-sulphate to measure the effect of diet on cysteine irreversible loss and absolute whole body protein synthesis (WBPS). Lambs fed pasture had the slowest (P<0.05) daily gains (116 g/day) and absolute WBPS (93 g/day) compared with lambs fed sulla (308 g LW and 152 g WBPS/day) or lucerne:sulla (281 g LW and 180 g WBPS/day). Lambs fed sulla had lower rumen NH3 concentrations (13.6 mmol/L), acetate:propionate ratios (2.6) and minor VFA concentrations (2.1%) suggesting less rumen proteolysis than lambs fed the other diets. Lamb performance was improved by feeding sulla or lucerne compared to pasture, and the lucerne:sulla mixture resulted in better performance than the average of the 2 species fed alone.