Effect of Different Processing Conditions on Amino Acid Digestibility of Feather Meal Determined by Chicken Assay

Abstract

An investigation was made of the effect of different processing conditions on feather meal (FM) by amino acid digestibility (AAD) determinations. Three processing times (30, 50, and 70 min) and three methods of treatments (without additions, .4% added NaOH, and .4% added proteolytic enzyme) were involved. The AAD of the test FM was measured by quantitative excreta collection over a period of 36 hr. All the test chicks were precision fed with 12 g of FM (dry matter), given in 2 doses with a 3-hr interval between feeds. Correction was made for metabolic plus endogenous excretions by using an N-free diet to distinguish apparent from true digestibility of amino acids (AA).The apparent and true digestibility of all individual AA were influenced by the processing conditions. There was a (linear-negative) time effect on the digestibility of all AA of the FM, with the exception of leucine. Significant differences in digestibility coefficients due to the method of treatment were found for cystine, tyrosine, phenylalanine, serine, and alanine. These AA values were lower in the chemically-treated FM. Comparison between the three methods of FM treatment revealed higher values for the enzymatically-treated samples and lower values for the chemically-treated ones, compared with samples treated without additions.Digestibility values for individual AA varied substantially. The values ranged in apparent digestibility values from 22.5% for lysine to 82.4% for isoleucinie and, in true digestibility values, from 36.3% for aspartic acid to 86.5% for isoleucine. The limiting essential AA, lysine, histidine, and methionine, in increasing order, were particularly low in digestibility. The unnatural AA lanthionine, present in all test FM, was not totally recovered in excreta and was found to be inversely proportional to its AAD.The results lead to the general conclusion that FM amino acids are affected in their biological digestibility by different processing conditions, time being the most significant one. Thus, FM protein should be used in poultry diets on the basis of the digested AA because of the large variations in digestibility between the individual AA.