A model for the description and prediction of the response of laying hens to amino acid intake

Abstract

A model which describes the response of groups of laying hens to different levels of amino acid intake is presented. The model is based on the assumption of simple linear relationships between amino acid intake and the output characteristics, egg production and maintenance, for individual birds. The response for a group of birds is then derived as the average of the individual responses. The shape of this flock-response curve depends on seven parameters, namely the mean maximum egg output (Ē max ), variation in E max, mean body weight (W), variation in W, the correlation between egg output and body weight, and two constants (a and b) representing respectively the quantities of amino acid required for unit egg output and for maintenance of unit body weight.Three methods of manipulating the model are described. These use (i) a computer simulation procedure; (it) the exact solution for the model and (iii) some reasonable approximations for practical application.The use of the model for describing experimental data and for predicting amino acid requirements is discussed, and the main limiting assumptions and some possible extensions of the principles involved are pointed out.

Predicting nutrient responses in poultry: future challenges

“…The method of interpreting these responses would depend on the reason for their measurement, but where the objective is to define the optimum intake of a nutrient, various methods of interpretation of such responses are still used in the literature in spite of the compelling review by Morris (1989) that concludes by pointing out the value of including marginal costs and revenues in such calculations. An integration of the responses of individuals making up a population results in a curved response, the so-called Reading Model of Fisher et al (1973), making it impossible to define a population 'requirement' for each nutrient no matter what form of equation is used to fit a curve to the data. It is always wrong to fit a broken stick model to a population response, as such a response applies only to an individual and not to a population, resulting in an underestimate of the optimum intake of the nutrient when applied to the population response.…”

“…Where marginal costs and revenues are included in the calculation, such responses may be used to determine the optimal economic intake of the nutrient by fitting the Reading Model (Fisher et al, 1973;Morris, 1989) to the data, and this may be of some value in laying hens whose requirements are relatively stable for long periods of time. However, in the case of growing birds the 'optimal economic intake' is meaningless, as, although it may apply to the period over which the trial was conducted, the requirements and hence responses of growing birds are changing continually over time.…”

“…Such responses are usually linear to the point where the genetic potential is reached (Fisher et al, 1973). Poultry nutritionists are interested in responses to nutrients in economically important outputs such as body weight (or protein) gain, breast meat yield, egg output, feed intake and conversion efficiency, numbers of chicks produced per hen, etc.…”

The response of weaned piglets to dietary valine and leucine

“…The response of pigs to VI at three Leu concentrations was analysed by fitting an exponential equation to the data and then comparing the responses at Valine and leucine in weaner pig diets each level of Leu using the Groups directive in Genstat (Version 12). In addition, the relationship between VI and carcass protein gain was determined using a statistical program that fits the Reading Model (Fisher et al, 1973) to the data for each Leu series (available from EFG Software, 2010). This program produces two coefficients that describe this relationship, namely, the amount of Val (mg) required per kg BW for maintenance, and the amount of Val (mg) required per g of protein gain.…”

Reading model to estimate optimum economic intakes of amino acids for poultry

“…II Animal and Poultry Science, University of KwaZulu-Natal (UKZN), Durban, South Africa. PRODUÇÃO ANIMAL aminoácido quando os modelos lineares, polinomiais e exponenciais eram ajustados aos dados de estudos dose resposta (CURNOW, 1973, FISHER et al, 1973, PILBROW & MORRIS, 1974. Em comum, os modelos lineares, polinomiais e exponenciais apresentavam boas estatísticas de ajuste e isso impossibilitava distinguir entre eles o melhor ou mais adequado por ferramentas estatísticas, disponíveis até então.…”