Shifts in seasonal temperatures and increased precipitation and varying rainfall patterns in the UK have largely been attributed to rising global temperatures. While many of us enjoy distinctly hotter summers than we have had in previous years, sporadic heavy rainfall, combined with warmer temperatures, subsequently result in greater grass flushes and extended growing periods than may be expected over the spring, summer and autumn months in the UK.

A recent review highlights the implications of excess adiposity on exercise performance in the sports horse. Writing in the journal Animals, Shannon Pratt-Phillips and Ahmad Muniizun described how owners of horse and pony breeds more susceptible to obesity, and those with existing or history of metabolic issues, may already be considering how best to manage their horses with consideration to changing grass growth.

The authors highlight that, for sports and performance horses with access to grazing, the situation may be more complex. For many top level performance horses who require a much higher feed energy content to match energy output when ridden, increased likelihood of lush grazing may be financially and logistically more of a help than a hindrance. But what about performance horses who may be more prone to weight gain, have reduced exercise levels either from injury or increasing age, or those who are working at a moderate level but may not require high levels of energy from feed?

Altered back dimensions from seasonal fluctuations in weight have been shown to significantly affect saddle fit, and excess adipose [AB1] tissue is known to result in a low-grade systemic inflammatory state in both humans and horses. Whilst levels of obesity in leisure horses are known to be high, performance discipline is also recognised as a risk factor for obesity – with show and dressage horses typically presenting with higher body condition scores than show jumpers.

A recent review article from researchers at the North Carolina State University, published in Animals, summarised the existing literature concerning the impacts of adiposity on exercise performance in horses. The review highlights the potential implications and risks of excessive weight gain on health and performance measures of sports horses, and particularly highlights research pertaining to owner’s opinions on body condition and the composition of a ‘healthy’ horse. Whilst the ethical and welfare implications of a severely undernourished and underweight horse are clear, it is concerning that many owners do not perceive obesity to also compromise welfare.

But what about the risks to our top level performance horses? The review highlights the increased risk of orthopaedic disorders in overweight horses, predominantly osteoarthritis, resulting from increased load-bearing on limbs and circulating pro-inflammatory compounds from adipose tissue, which gives credence to maintaining a leaner body condition for a longer athletic career. Altered stride kinematics on the flat, and jumping kinematics, have additionally been shown to be affected by additional weight carriage. Increased extension of the carpal and fetlock joints of the forelimb on landing, and higher mechanical force on the limbs when on the flat or jumping, are all factors which require consideration in the heavier horse.

Multiple areas of research have identified body weight having a negative influence on racing performance, with higher body weight associated with lower race times and increased oxygen consumption resulting in decreased time before reaching fatigue. Similar responses were identified in Dutch Warmblood horses, where riders and tack were weighted down – a proxy which we could use to estimate the impact of excess body weight on performance measures. It is therefore clear that the implication of excess adiposity on athleticism is relevant to not only racing speeds, but also performance on the flat.

Heat loss in exercising horses is reliant on blood transport and widening of capillary networks underneath the surface of the skin, production of sweat, and then loss of heat via evaporative cooling from sweating. The insulting properties of subcutaneous fat therefore poses negative implications for heat loss when exercising, and may be a compromising factor in exercise performance, particularly when exercising to sub-maximal levels in hotter conditions. The increased daily temperatures we have seen in the UK over May and June of this year may have posed challenges to heat dissipation in exercising horses, particularly those who are in higher body condition, a challenge which is likely to continue to occur given seasonal temperature shifts.

Given increasing levels of obesity across humans, horses and other domestic animals, it is clear the ‘obesity epidemic’ is showing minimal signs of receding. Whilst certain sporting disciplines may favour, or not penalise, horses in excess body condition, some owners will be hesitant to change their management and feeding practices. The maintenance of a healthy body condition is ultimately the owner’s responsibility, but until the equine industry and competition judges take a firm stance on penalising overweight and obese animals within athletic equine events, we may fail to see significant changes in horse body composition within certain disciplines.

There is a wealth of literature surrounding the negative health implications of long-term adiposity on humans, horses and other domestic animals, potentially resulting in cumulative health implications over the individuals’ lifespan. Whilst those competing in top level disciplines may be less likely to struggle with horse weight due to the level of exercise the horse is in, those of us with retired, hacking, unaffiliated or affiliated low- to moderate-level performance horses should take extra consideration when assessing body condition throughout the year. Encourage seasonal weight loss in the winter, base feeding regimes on the level of work the horse is in, utilise measurements for assessing weight and body condition, and implement weight-loss strategies where required. Considering the rising seasonal temperatures and increased rainfall, and the subsequent impacts on grazing quality and quantity, weight management strategies and monitoring may become the norm for many owners.

To read the full publication, click here.