Metabolic effects of altered body fat content in the Icelandic horse : responses to feeding and exercise

Abstract: Obesity is one of the most common welfare problems affecting domesticated horses and is believed to stimulate the development of other metabolic syndromes, i.e. insulin resistance and laminitis. The Icelandic horse is considered to be an „easy keeper“, indicating that it requires lower amount of feed compared to many other horse breeds to maintain its body condition. However, obesity and its effect is an unexplored subject in the breed. The aim of the thesis was to evaluate how altered body fat content affects metabolic- and physiological responses to feeding and exercise, respectively, in the Icelandic horse. The experiment was designed as a change-over study comprising of two experiments and two experimental periods. Ten Icelandic geldings, at the age of 6-8 years were used and equally divided into two groups and fed on different energy allowance over each period, restricted energy allowance diet vs. high energy allowance diet. The metabolic plasma profile was compared at the end of each treatment period by using a meal feeding trial and a standardised exercise treadmill test (SET). In the feeding trial collected blood samples were analysed for plasma insulin, glucose and non-esterified fatty acids (NEFA) and from the SET, blood samples were analysed for plasma glucose, NEFA and lactate. The results from the study showed that body condition (BCS) and body weight were positively correlated to each other as well as other assessed body parameters, indicating that greater number of assessed body parameters increases the accuracy of the estimated BCS. In the meal feeding trial, all horses irrespective of treatment showed normal metabolic responses. However, horses adapted to the high energy allowance diet had significantly higher plasma insulin concentration, but significantly lower plasma glucose and NEFA concentrations. In the standardised exercise treadmill test horses adapted to restricted energy allowance showed significantly higher plasma glucose and NEFA concentration and significantly lower plasma lactate concentration. They also reached significantly higher VLa2 and VLa4 implying a greater aerobic capacity. It was concluded that altered body condition and fat content affects the metabolic response to feeding and metabolic- and physiological responses to exercise. Keeping horses in a moderate body condition and physically active is of great importance. Feeding strategy and physical activity should be adapted to each other and maintained at a fine balance to positively affect the horse athletic abilities, enabling it to reach and maintain higher performance capacity in a healthy and sound state.