Dietary threonine for broilers: dietary interactions and feed additive supplement use.
2006
Kidd, M. T. | Hackenhaar, L.
The bird needs amino acids for numerous metabolic functions other than protein synthesis. As nutritionists, we assume that the estimated need of the limiting amino acid, determined by dose-response measurements, reflects the quantitative need of the bird. The global competitiveness of broiler meat production and the variable, and sometimes narrow, profit margins have strengthened the need to feed birds well-balanced diets that meet rather than exceed amino acid needs. The commercial production of L-threonine at prices attractive to least-cost broiler diet formulation has given nutritionists flexibility to decrease crude protein and closer meet the bird's amino acid needs. Care must be taken, however, to ensure that dietary amino acid needs are met, as modern commercial broilers accrete more meat (protein) at earlier ages than previous strains, so any shortage will negatively affect performance. Today, more nutritionists are utilizing the ideal ratio method of formulation. This method assumes ratios of essential amino acids to lysine. Since threonine is generally third limiting after methionine and lysine, the next most limiting amino acid will determine the value of threonine to the nutritionist. Therefore, commercial acceptance of L-threonine emphasizes the importance of accurately defining the minimum amino acid levels of the next limiting amino acids after threonine. Since the relative contribution of amino acids varies by ingredient, it is mportant that we have accurate analyses of all the essential amino acids in the range of ingredients used in formulation. This review discusses key factors that impact threonine needs and our current knowledge of amino acids limiting after threonine.
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