Energy utilization of twelve forages or mixed diets for maintenance by sport horses

Four experiments were performed to study the energy utilization of 12 diets fed near maintenance by adult standardbred horses (6 or 8 animals per treatment). The diets were composed of 5 types of forages fed alone or in combination with pelleted concentrate feeds (barley, maize, compound feed or dehydrated beet pulp). Diet digestibility (D) was measured over 6 day periods and energy expenditure (EE) by indirect calorimetry using two large open-circuit respiration chambers during 4 consecutive days. Organic matter (OM) digestibility ranged from 45.0 to 59.0% for bays and from 61.5 to 75.3% for mixed diets. Methane production averaged 2.0% and 3.5% of energy intake (EI) and digestible energy (DE), respectively. Metabolizable energy (ME) ranged from 84.6 to 90.5% of DE. Differences in efficiency of ME utilization were calculated from differences in ME requirements for maintenance (ME,) or maintenance plus 63 kJ gain per kg metabolic body weight (MEW) (ME 63). ME, and ME 63 were significantly lower with mixed diets than with hays: -11.8% and -10.2% when barley and maize supplied 61% or 45% of dietary ME, respectively. The results were discussed on the basis of differences in the energy cost of eating and the proportions of energy supplied by the absorbed nutrients from the various feeds. (C) 1997 Published by Elsevier Science B.V.