Alternative home-grown protein sources for ruminants in the United Kingdom

Improved sources of home-grown protein are required to substitute for animal proteins and soyabean meal in ruminant feeds. The present dominance of grassland feeds for protein supply in Britain is highlighted and possibilities for increasing microbial protein (MP) supply on grass-based diets are considered. There are particular opportunities for improving MP supply and animal performance from the use of grasses with increased content of water-soluble carbohydrates (WSC) and by the prevention of WSC and protein breakdown during ensiling through the use of bacterial inocula or chemical additives to restrict fermentation. Potential contributions from legumes and kale as alternative forages are reviewed. Whilst white clover and lucerne may give higher levels of MP than grass, this arises largely from high herbage protein concentration and high levels of feed intake, with large quantities of N being lost in excreta. There is evidence of natural protection of protein in red clover from polyphenol oxidase and in lotus and sainfoin by condensed tannins. These attributes may result in improved protein supply to the animal, but further research is required, particularly with silages. The grain legumes, peas and beans are not ideal protein supplements for grass silage because of their rapid degradation in the rumen, but are more suited as supplements to maize silage with low content of protein and good supply of readily available energy. Progress in plant breeding has opened up the possibility of increased use in Britain of lupins, which have much lower rates of degradation in the rumen than peas and beans and should form an effective complement to grass silage. (C) 2000 Elsevier Science B.V. All rights reserved.