Abstract

Four experiments, involving 62 animals, were undertaken to establish the effects of variations in Persian clover (Trifolium resupinaturn) and maize (Zea mays) silage consumption on the productivity of dairy cows at various stages of lactation. The research was specifically designed to exclude the effects of the substitution of one feed for another on the responses obtained. Feeding maize silage to cows fed 7-8 kg DM day-1 of Persian clover in early lactation resulted in marginal responses of 1.3-1.4 kg of milk per kg DM of supplement. As level of feeding increased, whether due to additional Persian clover or maize silage, returns to maize silage diminished. In late lactation, 0.9 kg of extra milk was produced from each additional kg DM of maize silage eaten. All of these responses were greater than expected and approached those reported for the use of high energy concentrates. However, there were two exceptions to this general conclusion. Firstly, at very low levels of Persian clover (4.0 kg DM/cow day-1), a protein deficiency prevented responses in milk as more maize silage was offered. Secondly, it was demonstrated that maize silage starch was also important to achieving good responses in milk yield. With only 5% grain in the maize silage in one experiment in mid lactation, the return to extra feeding was only 0.7 kg of milk/kg DM, which was below that obtained in both early and late lactation. The relationships of rumen parameters to differential feeding were variable. Ammonia concentration and acetate proportion both decreased as maize silage intake increased. Of the faecal variables measured, nitrogen concentrations were variable while lignin concentrations were negatively related to maize silage intake, and starch contents showed strong positive correlations.