Studies of apparent digestibility in horses and the use of internal markers

Abstract

The digestibility of horse feeds and rations can be determined by means of different techniques: calculations from the chemical composition of feeds, in vitro and in vivo methods. The aim of this research is to compare indigestible internal markers (acid-insoluble ash (AIA) and acid detergent lignin (ADL)) and total collection techniques for apparent digestibility estimation in horses. Analyses were carried out on two diets, different in concentrate quality, for dry matter, crude protein, crude fiber, ether extract, ash, fiber fractions NDF and ADF, AIA, nitrogen-free extract, organic matter and gross energy. Digestibility of all the parameters, excluding AIA and ash, were calculated on the basis of the total faeces collection and using alternatively AIA or ADL markers. Analysis of variance (ANOVA) was performed to study the different digestibility coefficients. The digestibility coefficients obtained using AIA are very close to those obtained with total collection. Both methods can then be used for digestibility trials in horses. The two diets involved different digestibility levels. Apparent digestibility cannot be estimated using ADL as an internal marker, because of the lack of recovery and consequent great underestimation of digestibility rates.