Adaptations to standard approaches for measuring total tract apparent digestibility and gastro-intestinal retention time in horses in training

Abstract

Conventional methods to assess total tract apparent digestibility and total mean retention time (MRT) in horses are based on a total collection of faeces during 5 or 6 consecutive days. The objective of this study was to assess some adaptations to these methods when applied to athletic horses, in order to minimize disturbances in their management and training schedule. The impact of a reduction of the collection period on both total tract apparent digestibility coefficients and MRT was evaluated. The reliability of acid insoluble ash (AIA) and lignin(sa) as markers for digestibility measurements and of a partial collection for liquid and solid phase MRT measurements was also examined, in comparison with the results obtained from total faecal collection. Six Arabian horses in endurance training, fed 8.0 kg meadow hay and 5.2 kg pelleted feed daily, were used. The total tract apparent digestibility of dry matter (DM), organic matter (OM), neutral detergent fibre (aNDFom), acid detergent fibre (ADFom) and hemicelluloses was measured from a total collection and a partial collection of faeces using AIA and lignin(sa) as markers, for 3-, 4- and 5-day collection period. Total MRT of Cr-EDTA, Eu-labelled hay and Yb-labelled concentrate was calculated using two algebraic methods based on the quantity or the concentration of excreted markers, for 1, 1.5, 2, 3, 4 and 5 days collection periods. The digestibility coefficients obtained with a total faecal collection were not affected when the collection period was reduced to 4 or 3 days, for DM, OM and the different fibre fractions of the diet. When lignin(sa) was used as a marker, reducing the sampling period to 3 days did not affect the digestibility coefficients of any of the constituents, and total tract apparent digestibility coefficients were under-estimated ( P<0.001) in comparison to those obtained by total faecal collection. When AIA was the marker, total tract apparent digestibility coefficients were lower ( P<0.05) with a 3-day collection period, than with 4- or 5-day period and the digestibility coefficients were over-estimated ( P<0.01) in comparison to those obtained by total faecal collection. A spot sampling faecal collection of faeces vs. a total faecal collection led to the same MRT values for both solid and liquid phases. A 1.5-day faecal collection led to the same MRT values as a 5-day faecal collection, whatever phase (liquid or solid) was considered. However, due to horses reactions to experimental conditions, a minimum faecal collection period of 3 days is recommended for assessing total MRT.