Methodologies for modelling energy and amino acid responses in poultry

Abstract

-The objective of this paper is to present some of the issues faced by those whose interest is to predict responses in poultry, concentrating mainly on those related to the prediction of voluntary food intake, as this should be the basis of models designed to optimise both performance and feeding programmes. The value of models designed to predict growth or reproductive performance has been improved inestimably by making food intake an output from, as opposed to an input to, such models. Predicting voluntary food intake requires the potential of the bird to be known, be this the growth of body protein or lipid, the growth of feather protein, or the rate at which yolk and albumen may be deposited daily in the form of an egg, and some of the issues relating to the description of potentials are discussed. This potential defines the nutrients that would be required by the bird on the day, which can be converted to a desired food intake by dividing each requirement by the content of that nutrient in the feed. There will be occasions when the bird will be unable to consume what is required, and predicting the magnitude of these constraints on intake and performance provides the greatest challenge for modellers. This paper concentrates on some issues raised in defining the nutrient requirements of an individual, on constraints such as high temperatures and the social and infectious environment on voluntary food intake, on some recent differences in the response to dietary protein that have been observed between the major broiler strains, and on the methodologies used to deal with populations of birds, and finally with broiler breeder hens, whose food intake is constrained by management, not by the environment.These issues suggest that there are still challenges that lie ahead for those wishing to predict responses to nutrients in poultry. It is imperative, however, that the methods used to measure the numbers that make theories work, and that the theories themselves, are robust and unambiguous such that the resultant models can be used to assist the poultry Industry to become more efficient especially when designing feeds and feeding programmes.

Lysine levels in diets for broilers from 8 to 21 days of age

“…The variations observed in the depositions of protein and fat in this study corroborate Leclercq (1998) and Gous (1998;2007), who state that increase in the limiting aminoacid concentration in the diet potentiates the deposition of protein and reduces fat deposition in broilers. Thus, reduction in the amount of fat in the carcass when higher lysine levels are used can be attributed to the increased energy expenditure for protein deposition and maintenance of greater muscle mass, providing a lower amount of energy for fat deposition (Leeson, 1995).…”

Maintenance requirements for methionine and cysteine, and threonine for poultry

“…Emmans (1981) suggested a 'maintenance unit' (BP m 0.73 .u) based on this theory. This scale has the added advantage of excluding body lipid from the unit of measurement: Expressing maintenance requirements on the basis of body weight or metabolic weight has been questioned because there is no demand for amino acids for the maintenance of lipid reserves (Emmans & Oldham, 1988;Burnham & Gous, 1992;Gous, 2007) which can vary considerably even among individuals with similar body weight (Emmans & Fisher, 1986;Emmans & Oldham, 1988;Burnham & Gous, 1992;Nonis & Gous, 2008). Thus, when comparing maintenance requirements between birds of different body weight and composition, body protein content of the bird at the time and in relation to its mature protein weight is preferred.…”

Effect of added dietary lysine and methionine above recommended levels, on growth performance, breast meat yield and financial returns in broilers

“…This causes the release of both amino and fatty acids from body reserves, leading to protein synthesis (Murray et al, 1998). If the above is true, then it can be speculated that in the current study, increases in dietary limiting amino acid concentrations may have increased protein synthesis and deposition (Gous, 2007) leading to improved yield in the breast meat and other carcass characteristics. Results from the present study agreed with the findings of Zhai et al (2016) who reported improved breast meat yield when the supplemental Lys and Met content of broiler diets were set at 120% and 140% of NRC requirements respectively.…”