Improving the nutritive value of timothy through management and breeding

Timothy (Phleum pratense L.) is a widely grown forage grass species in cool and humid regions of the world including northeastern and northwestern North America, Nordic countries, Russia, and Japan. The nutritive value of timothy decreases with time, phenological development, and increasing forage yield. This review paper summarizes methods of controlling or improving the nutritive value of timothy through management practices and genetic selection, while keeping in mind the importance of forage yield. Consequently, the nutritive value of timothy is considered in relation to the accumulation of forage yield. The ecophysiological basis for the decrease in nutritive value with increasing forage yield during a growth cycle is presented with the assumption that the forage is made of two components: metabolic and structural. The decrease in the proportion of the metabolic component with increasing forage yield reduces the nutritive value of timothy. The nutritive value is also affected by the N concentration of the metabolic component, and by the digestibility of the structural component. Harvest dates, growing seasons, N fertilization, and cultivars have an indirect effect on the nutritive value of timothy through increased forage yield and the change in the proportion of the metabolic and structural components, but they also have a direct effect on each component. The results presented demonstrate the possibility of dissociating yield and nutritive value by plant breeding and, therefore, to improve the nutritive value of timothy while maintaining forage yield.