Adaptation to a fat-supplemented diet by cutting horses

Abstract

Eight mature Quarter Horses were exercised by simulated cutting horse training in a repeated switchback experiment. Horses were fed a control (C) and a 10% fat-supplemented (F) concentrate with bermudagrass hay in a 60:40 ratio. A digestion trial was conducted prior to d 0, 7, 14, 21 and 28. Every 7 d a standardized exercise test (SET) was conducted utilizing a mechanical 'cow' device to stimulate anaerobic metabolism. Heart rate (HR), respiration rate (RR), rectal temperature (RT) and venous blood samples were taken prior to, during the SET and over recovery from the SET. Muscle biopsies were obtained from the biceps femoris before and after each SET. Body weight and condition were maintained on similar (P>.05) amounts of feed. (P>.05) amounts of feed. On d 7 the 'apparent digestibilities of energy, ether extract and neutral detergent fiber in F were higher (P<.05) than those in C. By d 14 apparent digestibility of crude protein was higher (P<.05) for F than C. There was no difference in HR between treatments or days. There were decreases (P<.Ol) in RR and RT over days, indicative of easier heat dissipation due to decreased ambient temperature (P<.06) and humidity (P<.Ol) because of seasonal changes. When horses were fed F, there was an increase (P<.05) in muscle glycogen storage from d 0 to d 28, however, values on a given d were not different from values when the horses were fed C. There was no increase in muscle glycogen over time when horses were fed C. On d 7, 14 and 28, muscle glycogen utilization increased (P<.05) from d 0 when horses were fed F, but values for glycogen utilization were not different between treatments on any d. Pre-exercise data was normalized to set d 0 values equal to zero, due to higher (P<.05) glycogen concentrations when horses were fed C than F. Consequently, d 28 pre-exercise muscle glycogen concentrations were higher (P<.05) when horses were fed F than C. Plasma lactate concentrations did not differ between treatments, however, there was a decline (P<.05) by days. Plasma glucose concentrations on d 28 when horses were fed F were lower than when fed C at numerous sampling times. Plasma oleate concentrations appeared to be higher when horses were fed F than C at all sampling times examined on d 14 and 28, and plasma linoleate concentrations increased on d 28 at rest and 30 min recovery when horses were fed F.