Evaluation of Two Equations for Prediction of Digestible Energy in Mixed Feeds and Diets for Horses

SIMPLE SUMMARY: Horses need energy from feeds consumed to maintain health and performance. Digestible energy is a common form to express the energy value of feeds for horses. Measurement of digestible energy in feeds requires animal assays that are difficult to conduct. Thus, several researchers have developed empirical equations to predict digestible energy in horse feeds from their chemical composition. In the present study, we evaluated two of those equations that predict digestible energy from the chemical composition declared on the label of commercial mixed feeds and diets in Europe. After testing both equations against 32 mixed feeds and diets of known digestible energy content, we found that one performed slightly better than the other although both provided acceptable predictions. Our results suggest that the effects of crude fiber on the digestibility of the other proximate components should be reexamined in both equations. ABSTRACT: Several authors have developed equations for estimating digestible energy in horse feeds as an alternative to the inconveniences of in vivo digestibility assays. We aimed to evaluate two of such equations. A dataset was constructed from the literature with 32 mixed feeds and diets of known proximate composition, whose digestibility was measured in in vivo assays. Then, the digestible energy of the mixed feeds and diets was predicted with both equations from their proximate components. Precision, accuracy, reproducibility, bias, and decomposition of total error of predictions were determined. Both equations performed almost equally well (R(2) = 0.89 vs. 0.87, root mean square error of prediction = 183 vs. 217 kcal/kg dry matter, concordance correlation coefficient = 0.91 vs. 0.86, and linear error = 24.6 vs. 33.6% of total error). Linear bias (p < 0.01 in both equations) resulted in overvaluation of low digestible energy feeds and, to a lesser extent, undervaluation of high digestible energy feeds and was significantly (p < 0.05) related to crude fiber. The obtained results indicate that the accuracy of both equations could be improved by reassessing the effects of crude fiber on the digestibility of the other proximate components.