Unfortunately, not all changes have been positive. The incidence of obesity in the equine population has dramatically increased. Currently around 70% of leisure horses are overweight or obese. Obesity and insulin resistance (IR) are major risk factors for laminitis, a systemic condition that presents as extreme foot pain and often warrants euthanasia. These conditions are recognised as the major welfare challenges facing domestic horses and ponies.
However, not all animals sharing a common pasture become obese and/or insulin resistant and some ponies develop laminitis in the absence of either factor. Horse and pony owners are acutely aware of the challenges of both maintaining body weight in elderly animals and minimizing the risk of laminitis in obese ponies. These concerns have been matched by an ‘owner-led’ demand for improved nutritional management of senior (older than 20 years) and obese (body condition score more than 7/9) animals.
The situation is complex and ‘simple solutions’ such as ‘feeding the horse more or less’ are far from simple to effect under domestic conditions, without causing further negative impacts on health.
Our research groups are working to understand why some animals are more susceptible to obesity and laminitis, in order to find practical solutions to minimise risk and to provide veterinary surgeons with evidence-based advice, with which to direct animal owners and managers. Local horse and pony owners, motivated to help find solutions to these issues, have been highly supportive of our work.
When we began, we understood very little about equine fat biology and its association with health in horses. We have developed robust, stable-isotope methods for evaluating ‘fatness’ and metabolic rate in horses and ponies and have improved our understanding of how fat deposited at specific anatomical sites can vary in function. With this knowledge we have been able to develop clinically-safe, nutritional protocols to promote controlled weight loss and decrease IR in obese animals.
These studies identified that not all animals respond in the same manner to the same weight loss diet. Some animals are relatively weight loss resistant and may require severe ‘dieting’ under veterinary supervision in order to lose weight. Linked studies have allowed us to explore variation in the glycaemic response of ponies to different feedstuffs.
Furthermore, horses depend on the bacteria which populate their guts to convert forage-foods to substrates they can use as energy sources. This ‘microbiome’ is altered in obese and old horses in a way that can leave them susceptible to metabolic disease when challenged with ‘energy-rich’ but commonly used foods, including grass and cereals. We have learned that the bacteria in spontaneously passed faeces are representative of the gastrointestinal microbiome.
Maintaining ponies of a common breed (Welsh Mountain ponies) and gender (mares), under normal but carefully standardised husbandry and nutritional conditions, allows us to minimise sources of variation between animals. These controlled conditions allow us to better understand the impact of age, body fat content and weight loss on the microbiome. This is important as the microbiome can be readily altered by changes in nutrition and it is possible that this work could lead to nutritional interventions which could help to reduce disease risk.
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