Effects of type and amount of rapeseed feed on milk production

Sixteen dairy cows were used in a 2 x 4 factorial experiment, where two rap eseed feeds (RSF) were compared at levels of 0, 1, 2 and 3 kg (fresh weight ) day(-1) replacing basal concentrate. The total amount of concentrate fed was 10 kg day(-1) and restrictively fermented grass silage was fed ad libit um. The experiment was arranged as a cyclic change-over design with four pe riods of 3 weeks each. The experimental feeds were rapeseed meal (RSM) and heat-moisture-treated rapeseed cake (RSC). Silage and total dry matter inta ke, milk production and milk constituent outputs were linearly increased as the proportion of RSF in the diet increased (at least P < 0.01). There wer e no differences between RSM and RSC. Increased RSF intake led to a linear increase (P < 0.001) in the concentrations of essential and branched-chain amino acids in the blood plasma of the cows. Feeding RSC resulted in higher concentrations of the essential amino acids histidine, isoleucine, leucine and valine (at least P < 0.05), but the concentration of methionine tended to be lower (P < 0.10) than on RSM diets. Utilization of amino acids absor bed from the small intestine (AAT) was not affected by dietary treatments, when feed table values, i.e. similar values for both RSFs, were used, but i t was progressively increased for RSM diets when AAT values based on rumina l and duodenal nylon bag incubations were used. This suggests that the nylo n bag method underestimated the protein value of RSM.