Life has returned to normal to a greater or lesser extent and most equine practices seem to be busier than ever. During lockdown there were concerns that there would be widespread abandonment of horses which thankfully does not appear to have happened. Further job losses and an economic recession may yet adversely affect equine welfare if owners are unable to afford the costs of feeding and caring for their horses. However, it is likely that the excesses of domestication will continue to be a greater threat to equine welfare than neglect. The perpetual tendency to overfeed our horses coupled with a year of reduced activity increases the risk of metabolic changes that in turn increases the risk of laminitis next year, if not before. Many horses had a summer of increased turn-out and reduced exercise, and have gained weight as a result (Figure 1).
Obesity and laminitis are already considered the greatest threat to equine welfare in the UK, with around half the horses in the UK being overweight or obese (Rendle et al, 2018). In the natural situation it is normal for horses and ponies to gain weight through the summer and lose in over the winter. This year, the extra weight gained over the summer may require some extra effort in ensuring weight is lost over the winter. Most horses will be stabled for a greater proportion of the day through the winter, giving owners a better opportunity to control and limit feed intake. This will ensure horses are lean going into next spring when sugar intake from grazing, and consequently laminitis risk, increases.
The increased attention around the association between human obesity and mortality from COVID-19 infection may provide an opportunity to discuss the adverse health impacts of equine obesity. In this strange new normal there cannot be many human interactions where COVID-19 does not come up as a point of discussion. There are parallels to be drawn between human and equine obesity as the latter is not only associated with laminitis but may also adversely affect health through the increased risks of hyperlipaemia, strangulating intestinal lesions, hastened inflam-ageing, osteochondrosis dissecans, increased blood pressure, perpetuating orthopaedic disease, preputial, mammary and/or ventral oedema and dermatitis. Obesity may also reduce athletic potential by increasing body mass, compromising respiratory function and prompting pharyngeal collapse (Rendle et al, 2018).
At the end of summer horses should be at peak condition and it is a logical time for veterinary surgeon and owner to work together to make plans for weight to be lost through the winter. By planning now, weight loss can be better controlled, more gradual, and should be possible without the need for crash dieting and adjunctive pharmaceuticals next spring.
Plans should focus on appropriate dietary restriction through the winter months but should also incorporate advice on rugging (or lack of it). They should include a means of monitoring progress such that non-compliant owners or truly weight loss-resistant horses can be identified in a timely manner and appropriate changes made to the plan.
For weight loss, a typical practical starting recommendation for a horse undertaking leisure or no exercise would be to feed a mature grass-based hay at 1.5% bodyweight (BW) unsoaked (assuming 90% dry matter (DM)) or 1.8% if it is to be soaked (assuming 20% loss of DM with soaking) to promote weight loss. Soaking is preferable as it allows a greater volume to be fed. It should be remembered that the effects of soaking are variable — any estimate is simply a starting point and will have to be adjusted according to the patient's response. There will be large variation in rates of weight loss in responses to dietary restriction. Some animals exhibit ‘weight loss resistance’ and may require repeated re-evaluation, further reduction in their feed intake and potentially the use of short-term levothyroxine as an adjunctive therapy. In addition to reducing sugar content, soaking hay will also reduce its DM, soluble protein, vitamin and mineral content so a protein, vitamin and mineral balancer should be fed. It is imperative that forage is weighed to ensure compliance (Figure 2).
In horses and ponies, up to 30% of the hay ration can be replaced by straw, to reduce calorie intake further while maintaining fibre intake. Donkeys will manage well on a 100% straw diet. Straw should be introduced gradually to help avoid gastrointestinal complications (and needs to be of high hygienic quality with the seed heads shaken free before feeding). If weight loss is not achieved having reduced feed to 1% of bodyweight as DM of low sugar (<10–12% water soluble carbohydrates) forage, and there are no doubts over compliance, treatment with levothyroxine might be considered.
Few horses need rugs when they are kept indoors out of wind and rain, even in very low or sub-zero temperatures, yet owners tend to assume their horse needs as many layers as they do. Adult horses are able to control their body temperature without any additional measures (e.g. rugs) at temperatures as low as 5°C (McBride et al, 1985). Native types that are acclimatised are capable of thermoregulating at temperatures well below freezing. As they become geriatric, horses may be less able to thermoregulate at lower temperatures and may require a rug when their younger stable mates do not. The need for rugging needs to be assessed on an individual horse basis based on age, type and bodyweight. Unnecessary rugging is a greater welfare concern than under-rugging, both by inhibiting the ability to thermoregulate in warmer weather and by perpetuating excess adiposity.
Exercise can be more challenging in the winter so every effort should be made to increase levels of exercise before the weather becomes more inclement. Even relatively short periods of exercise (20–30 minutes) will increase insulin sensitivity (Rendle et al, 2018). Exercise is not a substitute for an appropriate diet and without dietary restriction weight loss is unlikely even in the face of moderate exercise.
Pharmaceuticals should not be an excuse for poor compliance with weight loss protocols. However, levothyroxine is an effective means of inducing weight loss and increasing insulin sensitivity. Its use to augment weight loss through winter to reduce subsequent laminitis the following spring is logical. Induction of a hyperthyroid state wiThexogenous levothyroxine is safe even when horses are over-dosed 10-fold (Bertin et al, 2019). Treatment at a dosage of 0.1 mg/kg PO SID is recommended short-term until the desired level of weight loss is achieved. Once the target bodyweight is reached, the dose is decreased by 50% to 0.05 mg/kg for 2 weeks before being reduced by 50% again to 0.025 mg/kg for a further 2 weeks before discontinuing treatment.
Conclusions
As the evenings draw in, we should try to assess the body condition of all the horses we are examining and plan ahead to reduce the risk of laminitis and other obesity-related problems next year (assuming that these problems are not already present). Using a weigh tape should become as instinctive as donning a face mask in this strange new normal (Figure 3). This year more than previous years we need to be on high alert as horses have had a lazy summer of less exercise and increased grazing. The discussion around higher fatality rates in obese patients with COVID-19 and the current focus on tackling the human obesity crisis may be helpful in raising awareness of the harmful effects of equine obesity.
