The effect of duodenal ammonia infusions on milk production and nitrogen balance of the dairy cow

We hypothesized that an increased uptake of ammonia from the gut of dairy c ows would increase the use of amino acids for urea synthesis and decrease t he availability of amino acids for milk protein production, leading to a re duction in milk protein output. To test this hypothesis, four multiparous H olstein-Friesian dairy cows offered a constant diet based on grass silage w ere continuously infused with ammonium acetate (ammonia) or acetic acid (co ntrol) into the duodenum for 5 d in each period of a changeover design expe riment. Silage intake, rumen ammonia, pH and volatile fatty acid concentrat ions, and feces N excretion and whole body N balance were all unaffected by treatment, although urinary N excretion increased. Similarly, there was no effect of treatment on milk yields or on milk constituent yields. We concl uded that ammonia absorption represents a loss of protein to the animal, bu t that it is unlikely to result in reduced amino acid availability for prod uctive purposes such as lactation.