Effects of altered body weight and body fat content on performance, recovery response and locomotion asymmetry in the Icelandic horse

Abstract: The objective of this thesis was to investigate the effects of altered body weight and body condition score on physiological response to exercise in terms of performance, recovery and locomotion asymmetry in Icelandic horses. Obesity is a commonly rising problem in modern horse management. Related health disorders include laminitis and even impaired locomotion. The Icelandic horse is considered an easy keeper, with low energy requirements. It is therefore prone to obesity. The study was in a change-over arrangement, where nine horses were submitted to two different forage-only feeding strategies, a high energy allowance (HA, 64 MJ ME/day) and a restricted energy allowance (RA, 32 MJ ME/day), for a 28-day adaptation period followed by a week of data collection. The horses were trained five times a week. For data collection, the horses performed a standardized exercise test (SET) and a simulated breed evaluation field test (BEFT) together with locomotion asymmetry analysis. Blood samples were collected together with measurements of rectal temperature, respiratory rate and heart rate. The main results were that horses adapted to the high energy allowance had significantly higher body weight, body condition score and fat percentage. Altered body weight and body condition score affected the physiological response to exercise. Horses adapted to HA had lower judges´ scores in a BEFT for total score, gallop and for form under rider. Horses adapted to RA had higher plasma lactate. The RA horses moreover had higher mean speed and maximum speed during a BEFT, thus able to perform under higher exercise intensity. In the SET and BEFT, RA horses had higher haematocrit. In both exercise test, the recovery pattern of respiratory rate and rectal temperature was altered, indicating a decreased capacity to cope with exercise for the HA horses. The horses adapted to HA had higher front limb asymmetry compared to RA horses. With all the results combined, it is concluded that horses with higher body weight and body condition score have a decreased performance capacity at high exercise intensities.