Abstract
This study will determine the optimal ratio of amino acids (AA) essential (lysine, methionine and cystine, threonine, tryptophan, isoleucine, leucine, histidine, phenylalanine + tyrosine, glycine + serine, valine and arginine) for laying hens in the growth (initial, raising, breeding) and production phases (peak egg production) by the deletion method. In the first stage, will be determined the requirement for maintenance of nitrogen (NMR) and the maximum nitrogen retention potential (NRmaxT). Will be conducted four nitrogen balance tests, one for each period, with 56 birds each. The trial design will be completely randomized with seven treatments and eight replicates of each bird. The treatments are diets with graded levels of nitrogen made by the technique of dilution. Trial periods will be five days of adaptation diets, and a total of 10 days of excreta collection in the growth phase and 20 days to collect excreta and eggs at the production phase. The tests will be measured the nitrogen intake (NI), excreted (NEX) and deposited (ND = NI-NEX). The production phase will also be determined nitrogen in egg mass (NEM). The nitrogen retention (NR) will be calculated by the sum of them (NR = ND + NMR in growth and NR = ND + NOR + NMR in production phases). The NMR will be obtained by exponential ratio between NI and NEX, being obtained when NMR NI = 0. The NRmaxT will be determined by an exponential function of NR and NI, being NRmaxT the maximum point of the function. In the second stage, will be determined the ideal ratio between the essential amino acids (IAAR) for laying hens in the same phases. Trial periods will be the same as defined previously. Will be conducted four trials, one for each period, with 96 birds each. The trial design will be a completely randomized with 12 treatments and eight replicates of each bird. The treatments are a diet positive control (PC) and 11 diets with 30% deficiency of AA test for birds growing and 55% for birds production. For the formulation of diets deficient, CP diet is diluted with starch to meet 70% and 45% of requirements and again supplemented to meet the same levels of CP diet, except for the AA to be tested will remain deficient. Will be obtained the same previously defined variables. Based on the information obtained in the two tests, the efficiency of use of each AA will be calculated (bc-1) and IAAR be obtained by bc-1 division of lysine and the bc-1 the other AA test.
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