Nitrogen Efficiency and Amino Acid Requirements in Dairy Cattle

摘要

For more than 40 years, protein nutrition and metabolism in livestock animals has been a major subject for research. The beneficial effect of dietary protein on livestock performance and the relatively high value of protein-rich ingredients were mainreasons to assess the optimum dietary protein level. Scientists have long been aware of the high manure nitrogen (N) excretion and relatively low N use efficiency of livestock and the impact of manure N on the environment. In more recent years, public concerns over the impact of land use changes for feed protein production in combination with predicted increase in the demand for animal protein have become another stimulus to assess the optimum dietary protein level balancing animal performance and the ecological footprint of livestock production.Although ruminants are less efficient in feed protein use than monogastric livestock, the human edible protein efficiency is substantially higher than for monogastrics and is usually greater than 1.0, indicating that ruminants add to the total human foodsupply (Dijkstra et al., 2013b). This protein gain by ruminants results from the nature of plant proteins consumed by ruminants. Plant proteins for ruminants are often embedded in high-fibre forages (e.g. grass, clover) and high-fibre, inedible residues of the food industry (e.g. expellers, brewer's grains, gluten feeds) that are not potential foods for humans.