Over the past few decades, obesity has been of continuing cause for concern in the human population. Figures from a study conducted by the Health and Social Care Information Centre (Eastwood, 2013) reported a marked increase in obesity in the adult population from 13% in 1993 to 24% in 2011 for men and from 16% to 26% for women. In recent years an increase in obesity in both dogs and cats has been documented (German, 2010), and anecdotal evidence by equine veterinarians has suggested that obesity is a growing problem in leisure horses (Carter et al, 2009). Most of the literature published with regards to being overweight or obese focuses on the risk of health problems, such as diabetes and musculoskeletal problems (Thatcher et al, 2012), with little comment on how this affects the welfare of the animal.
Obesity in horses is a more complex issue; while it is comparatively easy to determine that a dog or cat is obese, the size of the horse makes recognition of excess bodyweight more difficult, particularly in larger framed horses (Owers and Chubbock, 2013). Another factor regarding recognition that obesity is both a health and welfare problem arises with the fact that owners must first recognise that their horse is obese, and secondly be prepared to do something about it. The matter is also further complicated by the problem that most of the health issues that arise secondary to obesity are not immediately life threatening to the animal and may not result in any obvious clinical signs of disease, thus owners can disassociate from the condition (Owers and Chubbock, 2013.
Definition and prevalence of obesity
Obesity is a qualitative term (Wyse et al, 2008), defined as the accumulation of excess fat (adipose tissue) within the body (Thatcher et al, 2012). It has also been defined as a disease in which excess fat has been deposited to such an extent that it has an adverse effect on general health; however, there is no accepted universal definition of obesity in horses and ponies (Geor and Harris, 2013). Within human research the definition is based upon epidemiologic data, which shows that with increasing body fat mass there is an increased risk of morbidity and mortality (German, 2013). While it is recognised that rare genetic defects (in humans), neutering (in dogs and cats) and some diseases such as hypothyroidism and hyperadrenocortism (in dogs) can be a risk factor for obesity, it is a positive mismatch between energy intake and energy expenditure that is the main reason why animals become obese (German, 2013).
It is estimated that one in five horses used for leisure in the UK are either overweight or obese (Stephenson et al, 2011). While it is recognised that this is a problem in the UK population of leisure horses, there have only been to date two published studies. A survey by Wyse et al (2008) and a pilot study by Stephenson et al (2011) looked at prevalence, owner perception of their horses' body condition score and owners' attitudes towards equine obesity. While it has been recognised that horse owners underestimate body condition and fatness, what is required is a UK-wide prospective study that uses standardised methods to assess body condition and fatness (Thatcher et al, 2012).
It is difficult to determine the exact number of horses that are owned for leisure purposes in the UK; the British Equestrian Trade Association (BETA) conducted a survey in 2011 and reported an estimate of 900 000 privately owned horses, not including the 88 000 horses owned by the professional sector. Wyse et al (2008) surveyed a population of leisure horses in the Glasgow area of Scotland (n=319), reporting a 45% prevalence of obesity. Likewise, the study by Stephenson et al (2011) reported a 54.1% prevalence of obesity in leisure horses surveyed in the counties of Leicestershire and Nottinghamshire. Both studies sampled a population of horses from a small geographical area, and yet within this small area the percentage of horses regarded as obese averages around 50%. This leads one to question the prevalence of obesity in the total population of leisure horses in the UK.
Obesity and welfare
Welfare is often seen by many to be a problem associated with neglect and cruelty to an animal (whether intentional or not), and for many the sight of a thin or emaciated horse would immediately raise welfare concerns. Why then is this not the situation for an obese horse? The problem is that subtle issues (such as obesity) are not always perceived as a problem by the public, and therefore affecting change is more difficult (Owers and Chubbock, 2013). There is, however, a ‘duty of care’ to feed horses correctly and to ensure that they are ‘free from pain and suffering’ (Argo, 2010).
Research has indicated that by using the Body Condition Scoring (BCS) system (Dugdale et al, 2012), a horse with a BCS >7 might constitute a useful welfare indicator of obesity, and might draw the attention of the public and veterinary staff to just how prevalent this problem is. In addition, this would also lead to veterinary staff being aware that obese horses were more at risk of secondary health problems. Veterinary practices are nowadays more likely to offer general health services to their clients and monitoring of body condition should be a routine part of a general health check as a means of determining whether the health and welfare of a horse is at risk.
Determining if a horse is obese
Body fat content in horses can vary widely, with figures of −3% to 45% being recorded by researchers (Argo, 2010). With an increasing number of horses being considered overweight or obese, a simple method by which changes in body fat content could be quantified and monitored is required (Dugdale et al, 2012). Figure 1 shows an image of a typical horse used for leisure riding. Could you advise an owner with regards to whether this horse is obese?
There are a number of ways in which horses can be measured in order to determine if they are overweight or obese, which are outlined below.
Bodyweight
Humans are regarded as obese if their bodyweight is 20–25% above the ideal weight (Laflamme, 2012). While it is common practice to use live weight in dogs and cats, weighing horses is not commonly undertaken as it requires the use of large weigh scales that would only be available at commercial yards. In addition, the optimum weight of a horse or pony is based on height, and currently there are no universally accepted weight ranges in the literature for owners to use as a guide for weight management. This is made more complicated when the many different breeds of horses are considered and associated breed differences in body type.
Where weigh scales are not available, it is common practice to use one of the commercially available weigh tapes that are produced and marketed by food manufacturers. A study by Ellis and Hollands (2002) looked at the use of four commercially available weigh tapes to estimate the weight of 2000 horses of differing ages, breeds and height. They concluded that while the use of weigh tapes was useful to provide an estimate of bodyweight, in horses over 14.2 hands high there was considerable variance in the accuracy of the weigh tapes because of greater individual variances in breeds, age and body types of the horses.
Body condition scoring (BCS)
BCS has been used in horses for many years in order to aid evaluation of the condition of the horse; it is a subjective, semi-quantitative method of evaluating body composition (German, 2013). The Henneke BCS system, which uses a nine-point scale to assess adiposity, was originally developed for use in Quarter horse broodmares, and subsequently adapted for use in other breeds of horse (Carter et al, 2009). Using this system, a BCS of 7 would indicate that a horse was overweight, while those with a BCS of 8 or 9 would be considered obese (Geor and Harris, 2013).
While classification of external body condition is useful, the fat content of the ‘flesh’ itself is highly variable, and internal fat depots cannot be visually assessed (Argo, 2010; Dugdale et al, 2012). Thus although the BCS provides a measure of ‘superficial flesh’, it does not assess subcutaneous fat independent of muscle mass (Geor and Harris, 2013). In addition, the system does not allow for differences in regional adiposity that may indicate increased risk for specific disease; for example, in humans abdominal (visceral) adiposity is associated with an increased risk for diabetes and cardiovascular disease (Carter et al, 2009). The accurate determination of the BCS of a horse that is already overweight is also difficult, as the key anatomical landmarks that are commonly used have already been obscured by fat (Dugdale et al, 2011, 2012).
Is important to remember, however, that BCS is easily determined by the horse owner, and an illustrated BCS system can be a useful tool for owner education (Laflamme, 2012). A study by Carter et al (2009) also suggested that the use of a ‘cresty neck scoring system’ (Table 1; Figure 2) could be useful for further evaluating the relationship between adiposity, metabolism and disease risk in horses and ponies.
| Score | Description |
|---|---|
| 0 | No visual appearance of a crest (tissue apparent above the ligamentum nuchae). No palpable crest |
| 1 | No visual appearance of a crest, but slight filling felt with palpation |
| 2 | Noticeable appearance of a crest, but fat deposited fairly evenly from poll to withers. Crest easily cupped in one hand and bent from side to side |
| 3 | Crest enlarged and thickened, so fat is deposited more heavily in middle of the neck than towards the poll and withers, giving a mounded appearance. Crest fills cupped hand and begins losing side-to-side flexibility |
| 4 | Crest grossly enlarged and thickened and can no longer be cupped in one hand or easily bent from side to side. Crest may have wrinkles or creases perpendicular to topline |
| 5 | Crest is so large it permanently droops to one side |
Body mass index
Body mass index (BMI) is used as a measure of adiposity in human literature and is measured using the formula ‘weight (kg) divided by height (m)2’; from this formula people can be classified as ‘overweight’ or ‘obese’ (German, 2013). BMI does not, however, differentiate between elevated body fat content and increased lean mass, and therefore is not an accurate measurement for athletic individuals (Geor and Harris, 2013). The use of morphometric measurements such as BMI are clinically used in human medicine; however, this method has been shown to have little application for the evaluation of adiposity in horses (Carter et al, 2009).
Potential causes of obesity
The role of adipose tissue is to provide a reservoir of fatty acids that can be used as an energy source during the postprandial fasting state; however, adipose tissue itself contributes little to basal energy expenditure as it uses little energy (Laflamme, 2012). As with many diseases, the cause of obesity is often multifactorial, with genetics and the environment being factors to be considered, in addition to overfeeding and limited exercise (Geor and Harris, 2013). Table 2 outlines some of the potential causes of obesity.
| Potential cause | Considerations |
|---|---|
| Overfeeding | Individual energy requirement affected by external factors, such as environmental conditions and level of exercise (including activity during turnout) |
| Use of high caloric density foodstuffs for horses or ponies spending much of the day in confinement and being used for occasional riding activities | |
| Horses or ponies kept permanently on pasture may have a greater caloric intake than required, especially during spring and early summer with an abundance of nutrient-rich forage | |
| Seasonal changes | In wild animals, appetite is highest during spring and summer to coincide with a plentiful supply of forage, and in winter appetite and metabolic rate decrease and energy stored in white adipose tissue is mobilised; these seasonal adaptations are also apparent in domesticated ponies |
| Horses and ponies nowadays have access to pastures with ‘improved’ forages, and across the seasons these have a much higher nutritional value | |
| Husbandry practices in winter months with additional hay and energy dense foodstuffs and provision of rugs and shelter will mitigate any winter-associated weight loss | |
| Genetics | While there is no published research in this area, it has been suggested that certain lines of horses and ponies have inherited genetic traits that allow them to better use poor or limited forage |
| Hormonal regulation | Two hormones, leptin and ghrelin, are recognised to have a major influence on energy balance: — ghrelin is primarily produced in the stomach and functions as an appetite-stimulatory signal and short-term mediator of energy balance (hunger hormone). It may play a role in appetite regulation in horses — leptin is primarily produced by adipocytes and provides information to the brain regarding availability of body fat stores. It regulates feeding behaviour by binding to the central nervous system (hypothalamus) and modulating neuronal activity in appetite control centres. It has been hypothesised that chronic overfeeding can lead to the development of leptin resistance, which may contribute to the maintenance of obesity |
| Lack of physical activity | The exact role of physical activity in the development of obesity in horses and ponies remains unknown |
Diseases and disorders associated with obesity
While it is outside the scope of this article to provide a detailed account of the diseases for which obesity has been proposed as a risk factor, Table 3 lists a number of diseases and disorders that have been associated with obesity in horses and ponies.
| Body system | Condition |
|---|---|
| Orthopaedic | Laminitis |
| Osteoarthritis | |
| Endocrine and metabolic | Equine metabolic syndrome |
| Insulin resistance | |
| Glucose intolerance | |
| Hyperinsulinaemia | |
| Dyslipidaemia | |
| Hyperlipaemia and hepatic | |
| Lipidosis | |
| Abdominal and intestinal disorders | Pedunculated lipomas |
| Miscellaneous | Heat intolerance |
| Exercise intolerance | |
| Exacerbation of an ageing-related proinflammatory state |
The veterinary nurse and client education
The veterinary nurse could play an important role with regards to improving the welfare of horses, as unlike many other welfare issues obesity can be addressed by educating owners with regards to husbandry practices (Wyse et al, 2008). Once obesity has been recognised as a problem by the owner, a management plan can be put into place; however, this must take into account the willingness and ability of the owner to control both the calorie intake of the horse and undertake a controlled exercise programme (Laflamme, 2012). It is also important to recognise that each horse is an individual and that there is no single programme that will be suitable for every horse; thus programmes must be tailored to suit the individual horse and owner, and in addition must be carefully monitored (Laflamme, 2012).
Weight management strategies and the role of the veterinary nurse
It is important that the horse is under the direct care of a veterinarian, and that the veterinary nurse is in communication with the veterinarian at all times. This article is not intended to provide an in-depth review of nutrition, and it would be advisable to consult with somebody qualified in this field. The following key points (Argo, 2010; Geor and Harris, 2013) are a starting point that could be used by veterinary nurses with regards to advising owners on this complex and often emotive issue.
Table 4 provides an outline of how the veterinary nurse could use the information below in order to develop a weight-loss programme. It is important to remember that the check list would need to be modified for the individual horse.
| Initial consultation | First follow up appointment |
|---|---|
| Appointment with veterinary nurse:
|
Determined by:
|
| History:
|
Initial goals from consultation:
|
| Clinical examination:
|
Initial goals from physical examination:
|
Conclusion
With current research suggesting that approximately half the population of horses used for leisure purposes in the UK is obese (Wyse et al, 2008; Stephenson et al, 2011), it is clear that more needs to be done by veterinary practices with regards to client education. The issue of equine obesity is complicated in that it is often either unrecognised, or not taken seriously, as a problem that affects the health and welfare of the horse. Determining whether a horse is obese or overweight is complicated as there are many ways in which this can be measured. In addition, horse husbandry and exercise is varied, and individual to each horse and owner. This means that devising a weight-loss programme can initially be a lengthy and time-consuming process.
The veterinary nurse is in an ideal position to provide a valuable addition to an equine veterinary practice with regards to the provision of a service aimed at educating the owner of the dangers of obesity in the horse, and also in the provision of both preventive programmes and specifically tailored equine weightloss programmes.