Response of Milk Synthesis to the Supply of Ammonia and Amino Acids

Milk protein content of cows in subtropical Queensland declines from the beginning of winter to the end summer and is a repeatable consistent observation across years. The genesis of such an event is hypothesised to lie in the nutritional and environmental changes that occur over this period with a change in forage type from the temperate species to the tropical species, a change in cereal grain supplementation and a reduction in intake associated with heat stress causing a change in the nutritional supply to the animal. A series of experiments examined the effect of high levels of ammonia absorption on milk production and milk components in dairy cows. The experiments used extensive, grazing trials with supplements of urea to increase ammonia absorption, and intensive, infusion of ammonia into cows indoors. Feeding urea in the supplement of cows grazing ryegrass increased milk protein significantly by 0.05 percentage units but had no effect on milk volume. Infusing ammonia intra-venously reduced milk volume (~ 20%) and milk protein content