ENERGY-UTILIZATION OF 12 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 animal s per treatment). The diets were composed of 5 types of forages fed al one or in combination with pelleted concentrate feeds (barley, maize, compound feed or dehydrated beet pulp). Diet digestibility (D) was mea sured over 6 day periods and energy expenditure (EE) by indirect calor imetry using two large open-circuit respiration chambers during 4 cons ecutive 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 productio n 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 fr om differences in ME requirements for maintenance (ME,) or maintenance plus 63 kJ gain per kg metabolic body weight (MEW) (ME 63). ME, and M E 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, re spectively. The results were discussed on the basis of differences in the energy cost of eating and the proportions of energy supplied by th e absorbed nutrients from the various feeds. (C) 1997 Published by Els evier Science B.V.