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CABI Book Chapter

Nutrient digestion and utilization in farm animals: modelling approaches.

Book cover for Nutrient digestion and utilization in farm animals: modelling approaches.

Description

This book contains 34 chapters on nutrition physiology and presents scientific research in modelling nutrient digestion and utilization in domestic animals, including cattle, sheep, pigs, poultry and fishes. It is divided into 6 parts that cover fermentation, absorption and passage; growth and development; mineral metabolism; methodology and model development; environmental impacts and animal prod...

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Chapter 29 (Page no: 328)

An ingredient-based input scheme for Molly.

The model described by Baldwin and co-workers (Baldwin et al., 1987; Baldwin, 1995) known as Molly utilizes a nutrient-based input scheme, where each nutrient is generally treated as a homogeneous substrate regardless of the source of that nutrient. The exception is a limited, discrete accommodation for fibre derived from grass versus legume. There are several limitations to such an input scheme: (i) failure to consider unique aspects of the varying input ingredients may result in prediction errors to the extent that the sum of individual ingredients deviate in character from the homogeneous nutrient assumed in the model; (ii) ingredient inputs are not specified and thus cannot be optimized directly; and (iii) it is rare to find a full listing of nutrient profiles in the published literature. Therefore, evaluations of model accuracy require reconstruction of the dietary nutrients from ingredients using other sources such as the National Research Council (NRC, 2001) as an approximation of the original ingredients. At the same time., an automated scheme for switching diet and animal inputs was needed to ensure data integrity of inputs and to allow consideration of varying animal and diet inputs when simulating multiple animals within and across experiments. The latter is required for parameter estimation. To address these issues, an input scheme was devised and incorporated into Molly that allowed ingredient-based diet specifications by an experimental unit with the ability to change diets within a run and across runs based on pre-specified criteria. The scheme utilized NRC ingredient values to generate the needed nutrient inputs for the model. Subsequent to these changes a large data-set was assembled from the literature and used to test the model. Prediction errors for most digestive parameters were found to be greater than 20% of the observed mean values. In most cases, mean bias was the major contributing factor to the prediction errors suggesting that reparameterization of the model was needed. However, in some cases, significant slope bias was observed suggesting that there may be some underlying model structure problems.

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Chapter details

  • Author Affiliation
  • Longview Nutrition Center, Land O'Lakes, 100 Danforth Dr., Gray Summit, MO 63039, USA.
  • Year of Publication
  • 2006
  • ISBN
  • 9781845930059
  • Record Number
  • 20063093915