Grass physiology and its relation to nutritive value in feeding horses

Abstract

Forage is the primary feed of the horse; it normally comprises more than 50% of the horse's diet on DM basis and it may supply 100% of the ration of many horse categories. Grasses are well adapted to frequent defoliation and to the presence of large herbivores, and consequently they cover, globally, large areas of natural and seminatural vegetation, and are also widely used in intensive forage production. As the Graminae is one of the largest plant families - over 600 genera - there is a large variation in the physiological mechanisms by which grasses react to environmental variables and management factors. In addition, humans utilize grass yield in several ways, i.e. as grazed grass, silage, haylage or hay. Consequently, crop physiology behind the grass yield is vast. In this paper we first describe on outline of plant physiology of grasses and main differences between C3 and C4 grasses as well as difference between forage legumes and grasses. Secondly, we focus on plant physiology of grasses that is of most relevance in the context of equine nutrition. We present an outline of key processes affecting the digestibility of grasses, since digestibility is the most important single feature of forage affecting the nutritive value. In addition, we cover fructan metabolism in grasses and its consequences in producing pasture, silage, haylage and hay. We also present a summary of effects of nitrogen on the production and nutritive value of grasses. We conclude that knowledge of plant physiology provides tools to understand the changes in forage quality and quantity. Based on this knowledge we have tools to choose the most proper management options in order to produce high quality forage for different types of horses.