Effect of age, live weight and dry matter intake on total tract nutrient digestibility in adult mares

The effects of age, live weight (LW) and dry matter intake (DMI) on the total tract digestibility of dry matter (DDM), organic matter (DOM), energy (DE), nitrogen (DN), neutral detergent fibre (DNDF), acid detergent fibre (DADF) and minerals (DCa, DK, DMg, DNa, DP and DS) were investigated in adult thoroughbred mares. Twenty mares, aged between 7 and 16 years (mean = 11.9; standard deviation ± 3.1) and weighing 508 to 650 kg (559.5 ± 36.7 kg) were offered 13 kg of feed per day consisting of 9 kg meadow hay, 3 kg barley and 1 kg lucerne chaff. Total faeces were collected over six days following a 20 day adaptation period. The average digestibility values were DDM: 0.59 ± 0.04; DOM: 0.63 ± 0.03; DN: 0.54 ± 0.08; DNDF: 0.44 ± 0.04, DADF: 0.38 ± 0.06, DE: 0.59 ± 0.04; DCa: 0.48 ± 0.08; DK: 0.68 ± 0.07; DMg: 0.27 ± 0.11; DNa: 0.63 ± 0.13 DP: 0.17 ± 0.11; and DS: 0.59 ± 0.05. Age was only related to DS. DMI (9.16 kg ± 1.1 kg) was negatively correlated (P <0.05) with DDM, DOM and DE while LW was positively correlated (P <0.05) with DDM, OM, DN, DNDF, DADF and DE. Mineral digestibility was not affected by LW or DMI. It is concluded that feed allowances should be adjusted for LW and/or DMI when a given amount of digestible nutrients are provided.