Although temperature pasture plants usually contain sufficient protein to potentially support most types of animal production, this protein is utilised for ruminant production with relatively low efficiency because of the losses that occur via microbial deamination in the rumen. These processes are well understood, yet procedures that should theoretically improve protein capture, such as the addition of soluble carbohydrate or protected protein to the diet, are frequently not effective. The paper considers reasons for this situation. It also examines several additional reasons why plant protein utilisation may be impaired, such as high rumen degradability, hepatic detoxification of absorbed ammonia and its associated costs in terms of amino acid catabolism, and the relationship between amino acid supply to the duodenum and tissue amino acid requirements. The paper evaluates whether an enhanced supply of individual amino acids, or mixtures of amino acids, to the tissues might increase the production of meat, milk and wool. It also considers whether we have enough information to be able to assess the likelihood of using specific enhanced amino acid supply or novel combinations to manipulate product quality. The efficacy of various mathematical models of protein digestion and metabolism are evaluated in relation to our current knowledge of the subject.
Proceedings of the New Zealand Society of Animal Production, Volume 57, , 4-8, 1997
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