477 - 2009 Poultry Science Association, Inc. Impact of...

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© 2009 Poultry Science Association, Inc. 2009 J. Appl. Poult. Res. 18 :477–486 doi: 10.3382/japr.2008-00105 Impact of dietary amino acid and crude protein levels in broiler feeds on biological performance G. M. Pesti 1 Department of Poultry Science, The University of Georgia, Athens 30602-2772 Primary Audience: Nutritionists, Researchers, Executives SUMMARY The concept of a requirement for dietary protein has been controversial since it was discov- ered that proteins are composed of amino acids and that some amino acids are dietary essentials for maximum growth and performance. In addition to the 10 essential amino acids and 3 that can be accreted only from limited substrates, poultry need a quantity of amino acids to synthe- size the other 8 that are needed to synthesize body proteins. Adding purified amino acids or amino acid precursors has been known for more than 50 yr to allow for reduced levels of intact proteins to provide adequate levels of essential and nonessential amino acids (CP). It has been recognized that individual essential amino acid requirements are functions of the total CP level. Increasing the total CP level while maintaining ideal ratios of essential amino acids increases growth, feed utilization efficiency, and carcass yields (i.e., decreases carcass fat). A published data set is used here to demonstrate 1) that potential problems arise from analyzing combined data sets inappropriately; 2) that in the overwhelming majority of studies, there is a positive response in growth ( P < 0.0002) and feed utilization efficiency ( P < 0.0002) to increasing di- etary protein levels; 3) that the relationships are much stronger in faster growing broiler strain birds; and 4) that there is no clear break point or “requirement” for CP in the range of dietary protein levels typically studied. Regardless of whether it is called “CP level” or “essential + nonessential amino acid level,” there is no clear requirement, only a smooth response curve that approaches maxima at lower levels for growth, and then feed utilization efficiency, and then lean meat yield, and finally the minimum for carcass fat. As a result, decisions on feeding levels for essential and nonessential amino acids should depend on the input-output relationships and costs. Key words: broiler , amino acid , crude protein , requirement , model DESCRIPTION OF PROBLEM The use of dietary CP level in feed formula- tion has been controversial since it was recog- nized that protein is merely the sum of amino acids in the feed ingredient, which may or may not be essential themselves. Before purified methionine was available, a typical corn- and soybean meal-based broiler starter feed had to contain approximately 71% soybean meal and 14% corn to supply minimal levels of the essen- tial amino acids. The feed had to contain 35.6% CP to supply all the essential amino acids at rec- ommended levels [1]. When synthetic D L -meth- 1 Corresponding author: gpesti@uga.edu , gpesti@bellsouth.net
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ionine became available, adding merely 0.23%
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477 - 2009 Poultry Science Association, Inc. Impact of...

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