Methodological review evaluates predictive models for feed energy in livestock diets, highlighting the superior precision of summative equations over empirical fiber formulas.
Accurate estimates of the available energy content of feeds are necessary to formulate diets and to evaluate the nutritional and economic value of different feedstuffs. Estimation methods must be rapid, inexpensive, and accurate before they are accepted widely by commercial feed testing laboratories. Currently, most laboratories use empirical equations based on ADF or NDF to estimate available energy content of feeds. Those equations are incorrect theoretically and lack adequate precision. Summative models that account for several sources of variation have been developed. These models are based on the composition of the fiber and nonfiber fractions. Adjustments are made to account for variations in digestibilities of fiber and protein and in the concentrations of fat and ash. Additional improvements are needed to ad- just for associative effects, feed intake effects, and physical characteristics of the feed.
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W.P. Weiss (1993) studied this question.
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