Rapeseed meal as a supplementary protein for dairy cows on grass silage-based diet, with the emphasis on the Nordic AAT-PBV feed protein evaluation system
The effect of rapeseed meal (RSM) supplementation on the performance of dairy cows on direct cut grass silage based diets was studied in five feeding trials. The proportion of RSM varied from 0% to 33% in the concentrate mixture (the grain was an oat-barley mixture of 1:1). In one experiment the treatments were RSM and soybean meal (SBM), while in another experiment forage was either grass silage or bam dried hay cut at the same maturity. In addition, this was compared to the data of other trials in Finland during the last ten years, in which RSM supplementation had been used. Using this data the response in terms of milk yield to RSM supplementation was estimated. The utilization of protein in milk production was estimated by the Nordic AAT-PBV protein evaluation system. During the experiments (1983-1990) the varieties of turnip rape were changed from high glucosinolate, containing single-zero, to low glucosinolate containing doublezero varieties, while the glucosinolate content was reduced from 40-50 μmoles to 14 μmoles per g of defatted meal. Heat-moisture treatment (™Öpex) further reduced the glucosinolate content by half. By replacing grain with RSM in the concentratemixture with ad libitum silage feeding, the silage intake increased by 0.43 kg per kg increase in RSM on the basis of dry matter (DM) (non significant). The response in increased milk production was 0.77 kg in milk or 0.70 kg in energy corrected milk (ECM) yield (P