Selecting higher nutritive value annual pasture legumes increases the profitability of sheep production

Abstract

CONTEXTThe nutritive value of annual pasture legumes changes with phenology during each season, with a progressive decrease in feeding value as plants accumulate structural carbohydrates and nutrients are diluted. However, these changes differ widely among annual legume species, affecting the pattern of nutrient availability and production in a grazing enterprise. OBJECTIVEThis paper set out to examine the implications of differences in the nutritive value of annual pasture legumes in relation to their economic value for mixed farming systems of southern Australia. METHODSCalibrated GrassGro™ plant models with data generated from field experiments to represent Dry Matter Digestibility (DMD) profiles of six annual legume species; Medicago truncatula Gaertn. (barrel medic), B. pelecinus L. (biserrula), Trifolium spumosum L. (bladder clover), Ornithopus sativus Brot. (French serradella), Medicago littoralis Rhode ex Loisel. (strand medic) and Trifolium subterraneum L. (subterranean clover). The plant models were used in a modelling study to support a self-replacing Merino sheep enterprise, which was simulated at seven locations across southern Australia, where annual pasture species are heavily relied on for livestock production. RESULTS AND CONCLUSIONSModelled values of DMD of green material, averaged across all phenological stages, ranged from approximately 62% (French serradella) to 73% (bladder clover), with little variation due to location. Pastures with higher nutritive value had a reduced requirement for supplementary feeding of sheep. Variation in nutritive value had a greater effect on supplementary feeding costs and gross margins than differences in biomass production among the annual legume species. Differences in the levels of supplementary feeding required in systems with the different legumes was most pronounced during the period from May to July (late autumn to winter). For sheep enterprises compared at the same stocking rate, the total supplementary feed required was 18% lower with bladder clover pastures, and 9% lower in subterranean clover pastures, compared with an average of the remaining four pasture species. SIGNIFICANCEThis is the first study to compare the effects of variation in nutritive value among the annual pasture legumes developed for the soils and climatic conditions of southern Australia. Our results demonstrated that the magnitude of differences in nutritive value among annual pasture legumes are economically important and that the establishment of higher nutritive value legumes will reduce supplementary feeding costs in extensive grazing systems, in some cases even where their biomass production is lower.