Nutritive value of forage legumes used for grazing and silage

Abstract

Legume forages have an important position in ruminant production in Western Europe\nand with further development can play an even larger role. Red clover for silage and white\nclover in grazed swards lead to enhanced growth rate and milk yield in comparison with\npure grasses. Much of the production benefit of these legumes relates to enhanced intake\nsince digestibilities are not markedly different to grasses. The higher intake of legume\nsilages reflects differences in the cell structure of legume plants which combined with\nhigh fermentation rates means that they break down into small particles in the rumen,\nand leave the rumen more rapidly than perennial ryegrass. Ease of ingestion leads to\nhigh rates of intake, which explains higher intakes for grazed legumes. A further benefit\nof legumes is the reduced rate of decline in digestibility with advancing maturity. Whilst\nlegumes have limited effects on gross milk composition or carcass characteristics, there\nare marked increases in levels of beneficial n−3 PUFA. Legumes have often led to a reduction\nin methane production from the rumen and again, this relates to both physical and\nchemical differences between forage species. The high rates of release of soluble protein\nand of breakdown to small particles from clovers and lucerne is associated with susceptibility\nto bloat, which is a limitation to further exploitation in grazing systems. The high\nconcentration of rapidly degraded protein in legumes also leads to inefficient utilisation\nof dietary N and increased urinary N output. Research with tanniniferous forages, such\nas birdsfoot trefoil and sulla, demonstrates the potential for future legumes with reduced\nenvironmental and health effects, though these particular forage legumes are not well\nadapted to temperate regions of Western Europe that are the focus of this review.