Grass silage: factors affecting efficiency of N utilisation in milk production

Key points Low efficiency of N utilisation for milk production in cows fed grass silage-based diets is mainly due to excessive N losses in the rumen. The type and extent of in silo fermentation can alter the balance of absorbed nutrients. There is very little experimental evidence that the capture of N in the rumen can be improved by a better synchrony between energy and N release in the rumen. Nitrogen losses in the rumen can be reduced by decreasing the ratio between rumen degradable N and fermentable energy. Rapeseed meal has increased milk protein output more than isonitrogenous soybean meal supplementation, probably due to higher concentration of histidine in rapeseed protein. Efficiency of N utilisation for milk production is not necessarily lower for the grass silage based diets compared to other diets.