Evaluation of ADL, AIA and TiO₂ as markers to determine apparent digestibility in ponies fed increasing proportions of concentrate

Abstract

Apparent digestibilities of feedstuffs can be estimated using either total faecal collection (TFC) or digestibility markers. However, it is still debatable whether the use of markers results in a reliable prediction of digestibility. Four adult ponies were fed four iso-energetic rations for 24 days with increasing proportions of pelleted concentrate (C) in relation to haylage (H), 100% haylage (100H); 75% haylage, 25% concentrate (75H:25C); 50% haylage, 50% concentrate (50H:50C); 25% haylage, 75% concentrate (25H:75C), respectively. The markers used were acid detergent lignin (ADL), acid insoluble ash (AIA) and titanium dioxide (TiO₂). The mean digestibilities of the organic matter based on TFC were found to be 56.9, 59.9, 64.9 and 69.8% for 100H, 75H:25C, 50H:50C and 25H:75C. Mean faecal recovery of markers as percentage of intake was 107.9 (SE 1.588), 118.9 (SE 1.726) and 97.1% (SE 0.927) for ADL, AIA and Ti, respectively. In this study digestibility values obtained using ADL and TiO2 did not significantly differ from those obtained with TFC. The coefficient of variance in faecal TiO2 and ADL excretion were 3.97 and 5.38%, respectively. Therefore, TiO2 seemed to be a suitable alternative to the TFC method in order to estimate apparent organic matter digestibility of diets differing in haylage to concentrate ratios.