The 15N-leucine single-injection method allows for determining endogenous losses and true digestibility of amino acids in cecectomized roosters.

Rujiu Hu,Jing Li,Fei Wang,Rab Nawaz Soomro,Xiaojun Yang,Junhu Yao,Yan Feng,Gotthard Kunze

doi:10.1371/journal.pone.0188525

Abstract

This study was conducted to assess the influence of dietary protein content in poultry when using the 15N-leucine single-injection method to determine endogenous amino acid losses (EAALs) in poultry. Forty-eight cecectomized roosters (2.39 ± 0.23 kg) were randomly allocated to eight dietary treatments containing protein levels of 0, 3%, 6%, 9%, 12%, 15%, 18% and 21%. Each bird was precisely fed an experimental diet of 25 g/kg of body weight. After feeding, all roosters were subcutaneously injected with a 15N-leucine solution at a dose of 20 mg/kg of body weight. Blood was sampled 23 h after the injection, and excreta samples were continuously collected during the course of the 48-h experiment. The ratio of 15N-enrichment of leucine in crude mucin to free leucine in plasma ranged from 0.664 to 0.763 and remained relatively consistent (P > 0.05) across all treatments. The amino acid (AA) profiles of total endogenous AAs, except isoleucine, alanine, aspartic acid, cysteine, proline and serine, were not influenced (P > 0.05) by dietary protein contents. The predominant endogenous AAs in the excreta were glutamic acid, aspartic acid, threonine, serine and proline. The order of the relative proportions of these predominant AAs also remained relatively constant (P > 0.05). The endogenous losses of total AAs determined with the 15N-leucine single-injection method increased curvilinearly with the dietary protein contents. The true digestibility of most AAs and total AAs was independent of their respective dietary protein levels. Collectively, the 15N-leucine single-injection method is appropriate for determining EAALs and the true digestibility of AAs in poultry fed varying levels of protein-containing ingredients.

Highlights

The accurate quantification of endogenous amino acids losses (EAALs) in the intestines of animals is crucial for determining amino acid (AA) requirements and for calculating the true AA digestibility of feedstuffs
The results showed that the 15N-enrichment of leucine in crude mucin (NLcm)/15N-enrichment of endogenous leucine in deproteinized plasma (NLp) ratios were not influenced by dietary crude protein (CP) levels
The contributions of endogenous leucine to total leucine in the excreta calculated as NLe0/NLp0 and NLcm/NLp were similar at the same dietary CP level

Summary

Introduction

The accurate quantification of endogenous amino acids losses (EAALs) in the intestines of animals is crucial for determining amino acid (AA) requirements and for calculating the true AA digestibility of feedstuffs. Cecectomized rooster method, linear regression and the nitrogen-free diet method [1] These methods can only be used to determine basal (or diet-independent) EAALs. Some dietary ingredients associated with “diet-specific” losses induce higher than basal losses [2]. Compared with the traditional 15N-isotope infusion method that involves the continuous infusion of a15Nlabeled AA [4,5,6], our method has advantages such as low cost and simplicity This method mainly relies on the assumption that the ratio of 15N-enrichment of endogenous leucine in excreta (NLe) to leucine in deproteinized plasma (NLp) remains relatively constant (i.e., the NLe/NLp ratio is a constant value) after the injection of a single bolus of 15N-leucine into birds fed different protein-containing diets. Because the value of NLe cannot be determined directly due to interference from undigested dietary leucine, obtaining an alternative technique that reflects the value of NLe is the key to evaluating the method

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Conclusion