Dietary protein is used inefficiently by lactating dairy cows, with approximately 75% of nitrogen intake excreted in manure. There are clear benefits of feeding lower protein diets that reduce the proportion of dietary N excreted in manure, but this strategy will only be acceptable to dairy farmers if potential negative effects on milk production and cow health and fertility are minimized.
In recent years numerous strategies for minimising the negative effect of lower protein diets on milk and milk protein production have been investigated, including feeding higher energy diets, synchronizing supplies of rumen degradable protein and energy, and feeding rumen-protected proteins and essential amino acids. However, most of the published information on feeding lower protein diets has been obtained using experiments with relatively short treatment periods that have not assessed potential long-term effects of chronic reduced protein intake.
We will review some of the strategies that have been investigated, as well as results from an on-going long term study at the University of Reading’s Centre for Dairy Research. In addition, we will consider the opportunity legumes offer for improving nitrogen use efficiency at a systems level, as well as some of the practical implications of low protein ration formulation.