Published online by Cambridge University Press: 02 September 2010
Six sport horses were given 1·26 times the measured maintenance energy requirement (MEm) from each of the four following diets: H1, meadow hay in the long form (organic matter digestibility OMD = 0·541); HMI, 700g/kg the same hay and 300 g/kg pelleted maize; HSBPI, 600g/kg hay and 400g/kg pelleted dehydrated sugar-beet pulp; SCFI, 500g/kg wheat straw and 500g/kg pelleted compound food (experiment 1). In experiment 2, eight sport horses were equipped with a portable device for recording feeding behaviour and fed at 1·31 MEm diet HI (meadow hay in the long form: OMD = 0·574).Circadian energy expenditure (EE) of horses was determined by indirect calorimetry using two large open-circuit respiration chambers. Horses were continuously standing. Increase in metabolic rate (IMR) during eating was calculated from the difference between the mean EE obtained during each eatingperiod and the corresponding resting EE. The mean daily ingestion rate of hay H2 amounted to 148 (s.d. 27)mg dry matter per kg metabolic body weight per min. IMR during the two main meals averaged 0·388 (s.d. 0·059) and was not significantly different between diets H1, H2, HM1 and SCF1. Expressed per kg dry matter intake, energy cost of eating (ECE) was similar for diets H2, H1 and SCF1 but significantly lower for HSBP1 and HM1 (P<0·05). ECE of simple foods was calculated from those of the diets and of hay: proportionately 0·010, 0·042, 0·102 and 0·285 metabolizable energy intake for pelleted maize, pelleted SBP, long hay and wheat straw, respectively.