Although not a new problem, equine obesity is becoming a globally recognised welfare issue. Through our work with The WALTHAM International Obesity Consortium which brings together world-leading veterinary, nutrition and research experts, we have been involved in equine obesity research for over 15 years. With the number of overweight horses and ponies seemingly on the rise, we wanted to share a few of the recent highlights with you…



  • Deuterium oxide dilution (a specialist blood test used to determine total body water and in turn calculate estimated fat mass) was recognised as the gold standard method for determining total body fat percentage in horses and ponies. As result, this method has since been used in a number of studies which has helped us to further our understanding of obesity.
  • Ponies were found to consume almost 1%* of their bodyweight when turned out for only 3 hours and almost 5% bodyweight* per day. This could equate to almost a whole bag of conditioning cubes for a 350kg pony living out at grass!

*dry matter

Horse at grass



  • It is recognised that horses and ponies with a body condition score of 7 or above on the 1-9 scale should be considered obese.
  • A study found weight loss to be highly individual with some horses and ponies identified as ‘weight loss resistant’, regardless of the type of diet used.




  • Insulin response was found to vary between breeds even in non-obese horses and ponies. This has helped us to understand that ‘insulin dysregulation’ does not only occur in overweight animals.
  • Prevalence of obesity in leisure horses was found to increase from 27.08% at the end of winter to 35.4% at the end of summer. Grass intake was found to be the major contributing factor in winter and summer, with supplementary feed and low intensity exercise having little or no effect.



  • A new ‘Body Condition Index’ (BCI) similar to the Body Mass Index (BMI) used in people was introduced. We continue to develop this tool to improve its accuracy across different breeds.
  • Feeding hay in a small-holed haylage net was found to slow eating time by only 5 minutes per kilogram – this would equate to just 30 minutes per night if feeding 6kg of hay!
  • Feeding 6kg of hay in 3, double layered, small holed haylage nets could extend eating time by 2 hours per night compared to feeding the same amount of hay in a single net.



  • Two studies confirm that obesity does not always result in insulin resistance and that importantly, the source of excess calories may have more of an effect on insulin response than obesity per se.
  • On average, grazing muzzles were found to reduce grass intake by 77% in spring, 78% in summer and 88% in autumn in ponies turned out for 3 hours.
  • On average, use of a grazing muzzle for 10 hours per day reduced the rate of weight gain in ponies living out at grass. However, results between individual horses and ponies vary.
  • Ever been on a crash diet and found that rapid weight loss is followed by further weight gain? A study in 2016 found that the severity of calorie restriction may affect the rate of future weight gain in horses too.



  • A new method for scoring internal fat in horses (EQUIFAT) was developed. It is hoped that this will help to improve our understanding of the role that internal fat plays in the development of conditions such as laminitis, insulin dysregulation and colic.
  • Can you spot an overweight horse? In one study, only 11% of horse owners or ‘managers’ correctly identified all overweight horses and ponies when asked to review a series of photographs.


EquiFat scoring system


Why is science important?

Obesity is associated with a number of health and welfare risks. In order to prevent and manage obesity successfully we must improve our understanding of why it occurs, the associated risks, and how best to manage individuals. We are far from having all of the of the answers but by continuing to invest in scientific research, we to hope collect as many pieces of the puzzle so that together, researchers, vets, nutritionists and horse owners alike can improve the health and welfare of horses and ponies throughout the world.


For more advice on feeding horses and ponies prone to weight gain contact the SPILLERS Care-Line



Argo  McC    ,   Curtis C ,   Grove-White D ,   Dugdale A,   Barfoot CF, Harris PA (2012) Weight loss resistance; a further consideration for the nutritional management of obese Equidae.  The Veterinary Journal 194 179–188


Bamford NJ, Potter SJ, Harris PA, Bailey SR. (2014). Breed differences in insulin sensitivity and insulinemic responses to oral glucose in horses and ponies of moderate body condition score. Domestic Animal Endocrinology Domest Anim Endocrinol 2014 Apr 9;47:101-107


Bamford, N. J., Potter, S. J., Harris, P. A. and Bailey, S. R. (2016), Effect of increased adiposity on insulin sensitivity and adipokine concentrations in horses and ponies fed a high fat diet, with or without a once daily high glycaemic meal. Equine Veterinary Journal, 48: 368–373


Bamford, N. J., Potter, S. J., Baskerville, C. L., Harris, P. A., & Bailey, S. R. (2016). Effect of increased adiposity on insulin sensitivity and adipokine concentrations in different equine breeds adapted to cereal-rich or fat-rich meals. The Veterinary Journal, 214, 14-20.


Bruynsteen L.  Moons C.P.H,  Janssens G. P. J., Harris P. A., Vandevelde K., Lefère L., Duchateau L. and Hesta  M. (2016)  Level of energy restriction alters body condition score and morphometric profile in obese Shetland ponies Vet J  2016 (1) 61- 66

Dugdale, A. H. A., G. C. Curtis, Milne E, Harris PA  & Argo C Mc (2011b). Assessment of body fat in the pony: Part II. Validation of the deuterium oxide dilution technique for the measurement of body fat. Equine Veterinary Journal 43(5): 562-570


Dugdale A,. Curtis GCCripps P. Harris PA.,  & Argo CMcG   (2011c)  Effects of season and body condition on appetite, body mass and body composition in ad libitum fed pony mares Vet J 190 p 329 -337.


Dugdale A,. Grove-white – D , CurtisGCCripps P. Harris PA.,  & Argo CMcG   (2012) Body condition scoring as a predictor of body fat in horses and ponies The Veterinary Journal 194   173–178


Ellis ADE, Fell M, Luck K, Gill L, Owen H, Briars H, Barfoot C & Harris PA (2015a) Effect of forage presentation on feed intake behaviour in stabled horses . Applied Animal behaviour Sciences 165 p 88 94


Ellis A. D., Redgate S., Zinchenko  S., Owen  H.  Barfoot  C.,  & Harris P. (2015b) The effect of presenting forage in multi-layered haynets and at multiple sites on night time budgets of stabled horses Applied Animal Behaviour Science 171 p 108-116


Giles, S.L., S.A. Rands, C.J. Nicol, et al. 2014. Obesity prevalence and associated risk factors in outdoor living domestic horses and ponies. PeerJ 2:e299.


Longland A, Barfoot C, Harris P (2016a) , Effects of grazing muzzles on  intakes of dry matter and water-soluble carbohydrates by ponies grazing spring, summer and autumn swards, as well as autumn swards of different heights Journal of Equine Veterinary Science  40 26-33.


Longland A, Barfoot C, Harris P (2016b) Efficacy of wearing grazing muzzles for 10 hours per day on controlling bodyweight in pastured ponies Journal of Equine Veterinary Science 45 22 – 27.


Morrison PK,  Harris PA,  Maltin CA,  Grove-White D  McG. Argo C McG (2017a)  Perceptions of obesity and management practices in a UK leisure-based population of horse owners and enthusiasts Journal of Equine Veterinary Science 53, June,   19–29


Morrison PK, Harris PA, Maltin CA, Grove-White D, Argo CM (2017b) EQUIFAT: A novel scoring system for the semi-quantitative evaluation of regional adipose tissues in Equidae. PLoS ONE 12(3): e0173753. doi:10.1371/journal.pone.0173753


Potter SJ, Harris PA, & Bailey SR (2015) Derivation of a new body condition index to estimate body fat percentage from morphometric measurements: comparison with body condition score. JEVS 35 p 410  - 411