Feeding high energy supplements to pasture-fed dairy cows. Effects of stage of lactation and level of supplement

Abstract

Five experiments were done in which stall-fed dairy cows were provided with a basal ration of pasture (6-7 kg DM) which was supplemented with varying amounts of a pelleted, high energy supplement (0-10 kg DM). Forty-seven cows at various stages of lactation were fed in this manner for up to 5 weeks. Responses to feeding the supplement depended on the stage of lactation at which the supplement was fed, and the amount of the supplement consumed. Marginal responses in milk production fell from 1.6 to 0.7 kg milk per kg supplement as lactation progressed, and as the level of feeding increased. Although responses in milk fat yield also decreased as lactation advanced, there was also a reduction in milk fat production when more than about 6 kg DM of supplement were fed. This was due to a severe depression in the fat content of the milk, which was found to be associated with intakes of diets with less than 250 g kg DM-1 neutral detergent fibre; diets with less than this level of fibre resulted in ratios of lipogenic to glucogenic volatile fatty acids in the rumen below 4:1. This occurred when the supplement constituted 0.4-0.5 of the diet on a dry matter basis. In addition, rumen ammonia levels were low when large amounts of supplement were fed. With all rumen characteristics, stage of lactation had no influence on values.