Submitted to: British Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2003
Publication Date: 2/1/2004
Citation: Kidd, M.T., Burnham, D.J., Kerr, B.J. 2004. Isoleucine needs of ross male broilers. British Poultry Science. 45:67-75. Interpretive Summary: Research conducted on the isoleucine requirement of broilers is extremely limited. In addition, validation of isoleucine-deficient assay diets were seldom carried out, the energy and protein levels of assay diets were different from the levels used in practice today, and the isoleucine digestibility of the basal diets was not known. Thus, estimates of the isoleucine requirement of broilers (National Research Council Subcommittee on Poultry Nutrition, 1994) were based on (calculated) factorial estimates rather than on empirical evidence. As environmental issues with nitrogen losses from livestock operations becomes more pressing and as the availability of crystalline amino acids becomes more economically viable, understanding amino acid limitations in low crude protein diets and their desired concentration in feeding programs for optimal production (performance and carcass composition) and minimal nitrogen excretion, is paramount to the broiler industry. Experimentation indicated that a red blood cell-based diet was determined to be markedly deficient in isoleucine, but fully efficacious when fortified with surfeit isoleucine. The results from this research suggest a requirement estimate range of 0.67 to 0.71% total isoleucine for birds from 18 to 30 days of age, 0.64 to 0.66% total isoleucine for birds from 30 to 42 days of age, and 0.55 to 0.66% for birds from 42 to 56 days of age. Research results described in this report provides nutritionists at universities, feed companies, and broiler production units vital data on how to clearly define the isoleucine needs of broilers to properly formulate their diets to optimize growth performance and ultimately to minimize nitrogen excretion.
Technical Abstract: Isoleucine (Ile) needs of growing and finishing Ross x Ross 308 male broilers were measured by evaluating growth performance and processing attributes in six floor pen experiments. The degree of deficiency of the mash Ile test diet (corn, soybean meal, and blood meal based) and the ability of it to support growth equal to that of a mash diet based on corn and soybean meal containing surfeit Ile was measured in Experiments 1, 2, and 3 from Days 18 to 30, 30 to 42, and 42 to 56, respectively. In all time periods, the Ile deficient test diets (31% lower than the 1994 NRC Ile recommendations) reduced (P < 0.05) growth and carcass weights of birds and the test diet containing surfeit Ile restored growth and carcass weights (P > 0.05) equal to that of birds receiving the corn and soybean meal diets. Because the Ile response was validated, the Ile need (95% of the asymptote from the quadratic model) was measured for growth and carcass needs from Days 18 to 30, 30 to 42, and 42 to 56 in Experiments 4, 5, and 6, respectively. Recommended needs for Ile are expressed as total percentage of diet and the digestible Ile coefficient is 90.4%. The Ile needs from Days 18 to 30 for BW gain and feed:gain were 0.68 and 0.71%, respectively. From Days 30 to 42, BW gain and feed:gain Ile needs were 0.64 and 0.66%, respectively. Significant, quadratic carcass responses for this period did not occur. From Days 42 to 56, Ile needs for BW gain, breast meat weight, and breast meat yield were 0.55, 0.60, and 0.63% of diet, respectively. Dietary Ile needs for live performance in Ross male broilers were well below published values (NRC, 1994). The Ile minimums can be used in feed formulation to reduce protein while taking advantage of commercially available feed grade amino acids and minimizing dietary amino acid excesses.