Growth and plant development of tropical forages is vari- able throughout the year and affected by several environmental factors. Cool temperatures, low levels of solar radiation and low rainfall are among the environmental constraints that have been associated with lower production during the winter months. Simulations of forage growth in tropical locations (Sinclair et al., 2005) indicated that daylength may play a major role in the observed decreases in forage production during the short- daylength period of the year.