A comparison of methods to estimate nutritional requirements from experimental data

Abstract

1. Research papers use a variety of methods for evaluating experiments designed to determine nutritional requirements of poultry. Growth trials result in a set of ordered pairs of data. Often, point-by-point comparisons are made between treatments using analysis of variance. This approach ignores that response variables (body weight, feed efficiency, bone ash, etc.) are continuous rather than discrete. Point-by-point analyses harvest much less than the total amount of information from the data. Regression models are more effective at gleaning information from data, but the concept of "requirements" is poorly defined by many regression models. 2. Response data from a study of the lysine requirements of young broilers was used to compare methods of determining requirements. In this study, multiple range tests were compared with quadratic polynomials (QP), broken line models with linear (BLL) or quadratic (BLQ) ascending portions, the saturation kinetics model (SK) a logistic model (LM) and a compartmental (CM) model. 3. The sum of total residuals squared was used to compare the models. The SK and LM were the best fit models, followed by the CM, BLL, BLQ, and QP models. A plot of the residuals versus nutrient intake showed clearly that the BLQ and SK models fitted the data best in the important region where the ascending portion meets the plateau. 4. The BLQ model clearly defines the technical concept of nutritional requirements as typically defined by nutritionists. However, the SK, LM and CM models better depict the relationship typically defined by economists as the "law of diminishing marginal productivity". The SK model was used to demonstrate how the law of diminishing marginal productivity can be applied to poultry nutrition, and how the "most economical feeding level" may replace the concept of "requirements".

Estimation of the optimal ratio of standardized ileal digestible tryptophan to lysine for finishing barrows fed low protein diets supplemented with crystalline amino acids

“…Quadratic models can effectively estimate increases and decreases, and the shape of the curve represents the response to graded concentrations of a nutrient up to the point when it becomes "safe" or "meets requirements" (Pesti et al, 2009). Their advantage over linear models consists in that they more accurately describe the physiological course (Robbins et al, 2006).…”

“…Their advantage over linear models consists in that they more accurately describe the physiological course (Robbins et al, 2006). However, these models may not be appropriate if the response criterion does not further respond to a higher level of nutrient, and their estimates are influenced by additional input levels below or above the requirement (Pesti et al, 2009). In addition, the quadratic estimation of the amount of AA to reach 100% of the maximum commonly overestimates the requirement (Baker, 1986).…”

Response of pullets to digestible lysine intake

“…The theoretical assumptions of each model can aid in the empirical interpretation of the responses to different nutrient intakes that directly affect the optimal intake (Pesti et al, 2009).…”

“…The responses obtained by this methodology are extrapolated to the population using mathematical functions (Pesti et al, 2009).…”

A hybrid model of uniform design and artificial neural network for the optimization of dietary metabolizable energy, digestible lysine, and methionine in quail chicks

“…from economic point of view, the values estimated as "requirements" may be different from those to obtain profit maximization (Pesti et al, 2009). The estimated values in this study may not be economical in practice as the most economical feeding level may replace the concept of "requirement" in the poultry industry.…”