Abstract
ABSTRACTThis study examined the effect of altered body weight (BW) and body fat content on exercise performance and recovery. Nine horses were divided into two groups, and changes in BW and fat content were induced by feeding a high (HA) or restricted (RA) energy allowance for 36 days in a cross‐over design. In the last week of each treatment, BW and body condition score (BCS) were recorded, body fat percentage was estimated using ultrasound, and a standardized incremental treadmill exercise test (SET) and competition‐like field test were performed (scored by judges blinded to treatments). Blood samples were collected, and heart rate (HR), rectal temperature (RT), and respiratory rate (RR) were also recorded. Objective locomotion analyses were performed before and after the field test. Body weight, body fat percentage, and BCS were higher (5–8%) in HA than in RA horses (p < 0.05). In SET, HA horses showed higher HR, plasma lactate concentration, RR, and RT than RA horses (p < 0.05), and lower VLa4, hematocrit (Hct), plasma glucose, and plasma NEFA concentrations (p < 0.05). Hct was also lower in HA horses in the field test, while RA horses showed higher scores (p < 0.05). After both tests, resting plasma lactate concentrations were reached faster in RA than in HA horses (p < 0.05). Objective locomotion asymmetry was higher in HA than in RA (p < 0.05). These results clearly show that increased BW and body fat content in horses lower physiological fitness in terms of VLa4, plasma lactate removal, Hct levels, plasma glucose availability and reduce true performance evaluated by blinded judges.
Highlights
In human athletes, it is generally accepted that body fat content can have marked effects on exercise performance, even in non-overweight people (Lewis et al, 1986; Poortvliet et al, 2001)
There is a lack of controlled studies using e.g., a cross-over design, but field studies have examined the relationship between body condition, body composition, and performance in endurance horses (Garlinghouse & Burrill, 1999; Lawrence et al, 1992), Standardbred trotters (Kearns et al, 2002; Leleu & Cotrel, 2006), and Thoroughbred racehorses (Fonseca et al, 2013)
Other studies have shown a positive correlation between race time and body fat content in Standardbred horses (Kearns, McKeever, Kumagai, et al, 2002), a negative correlation between VO2max and body fat percentage in Standardbred horses (Kearns et al, 2002), and a negative correlation between lactate threshold (VLa4) and body fat percentage in French Trotters (Leleu & Cotrel, 2006)
Summary
It is generally accepted that body fat content can have marked effects on exercise performance, even in non-overweight people (Lewis et al, 1986; Poortvliet et al, 2001). A recent study on training responses by Klein et al, (2020) showed lower body fat percentage and improved performance (run time to fatigue) in geldings compared to mares subjected to the same training program and ad libitum feeding. Whether these effects are due solely to altered weight-b earing or partly to altered metabolism has not yet been clarified.
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