ADAPTATION TO A FAT-SUPPLEMENTED DIET BY CUTTING HORSES

In a crossover experiment, eight mature Quarter Horses were exercised by simulated cutting-horse training and fed either a control concentra te (C) or a 10% fat-supplemented concentrate (F) with Bermuda grass ha y in a 60:40 ratio. The experiment consisted of two 28-day experimenta l periods with a 28-day standardization period between treatments. Dig estion trials and standardized exercise tests (SET) were conducted eve ry 7 days during experimental periods, Dietary fat had no detrimental effect on digestion of diet constituents, and all digestion coefficien ts were within expected ranges. Likewise, there was no significant dif ference in heart rates between treatments or SET days. Plasma lactic a cid concentrations did not differ (P > .05) between treatments, howeve r, there was a decline (P < .05) with advancing SET day. When horses w ere fed fat, there was an increase (P < .05) in muscle glycogen storag e from days 0 to 28, but there was no increase (P > .05) in muscle gly cogen over time when horses were fed C. On days 7, 14, and 28, muscle glycogen utilization increased (P < .05) from day 0 when horses were f ed fat but not C. Pre-exercise data were normalized such that day 0 va lues equaled zero, due to higher (P < .05) glycogen concentrations for C than F on day 0. Subsequently, muscle glycogen concentrations on da y 28 before exercise were higher (P < .05) when horses were fed F than C. The results of this study indicate that Quarter Horses in simulate d cutting-horse training can adapt to digestion of a fat-supplemented diet by day 14. However, it may take up to 28 days of adaptation to a fat-supplemented diet to observe increases in glycogen storage and use .