Ruminants may absorb large quantities of ammonia resulting from microbial fermentation and incomplete capture of rumen degradable protein (Huntington, 1984, 1987). Detoxification of this ammonia by ureagenesis in the liver involves the use of aspartate, and although this can be derived from ammonia via glutamate, it may be drawn from the general body amino acid pool. If the latter occurs, the availability of amino acids for milk production may be reduced, leading to a reduction in the quantity and/or quality of milk produced. This experiment was designed to investigate the effect of infusing ammonia into the duodenum of dairy cows on the quantity and quality of milk produced.

Four multiparous Holstein-Friesian dairy cows fitted with duodenal cannulae were given one of two experimental treatments based on duodenal infusions in a changeover design with three periods (the last period of a four period design was not completed). Duodenal infusions were chosen to avoid direct effects on rumen parameters.