Effects of exercise on voluntary intake, morphometric measurements, and oral sugar test response in horses on ad libitum forage

In a previous study, exercise resulted in weight loss and improvements in insulin and glucose metabolism, but horses on free-choice forage may increase feed intake in response to exercise, potentially negating the benefits. This study aimed to determine if light exercise increases intake in mature horses, and if horses on ad libitum forage achieve the benefits previously observed. Eight mature, stock-type geldings (594.3 +/- 50.5 kg; 12.0 +/- 1.7 yr) were adapted to a diet of ad libitum grass hay. Baseline dry matter intake (DMI) was measured for 7 d. Horses then remained idle (CON, n=4) or entered an exercise program (EX, n=4) for 3 weeks. Voluntary DMI was quantified daily. Body weight (BW), heart girth (HG), girth to height ratio (G:H), neck circumference (NC), neck circumference to height ratio (NC:H), rump fat thickness (RF), percent body fat (BF), serum insulin, plasma ghrelin, and plasma leptin were quantified weekly. An oral sugar test was conducted on day 0 and 21, and insulin to glucose ratio (Ins:glc) and 60-min insulin sensitivity index (ISI60) were calculated. Statistical analysis was performed using repeated measures. Insulin, ghrelin, Ins:glc, and ISI60 were not normally distributed, so they were log-transformed for analysis. P <= 0.05 was considered significant. The EX group showed no difference in DMI or (log) ghrelin compared to the CON group. The CON group showed increases in BW, RF, and BF, while the EX group showed decreases in HG, G:H, NC, NC:H, (log) insulin, and leptin. EX showed lower (log) Ins:glc than CON after treatment. Overall, light exercise did not alter DMI in mature horses on ad libitum forage, but resulted in improvements in morphometric measurements, (log) Ins:glc, and plasma leptin concentrations, and avoided gains in BW and rump fat.