Obese Horses Lose Weight on Free Choice Hay - Research Reflection

By Juliet M. Getty, Ph.D.

Researchers from the University of Melbourne, Australia, and the WALTHAM Centre for Pet Nutrition in the United Kingdom examined how much weight obese ponies and horses lost when fed all the hay they wanted (ad-libitum). They also looked at weight loss when forage was restricted.

Twelve obese animals were used in this study: 4 Standardbreds, 4 mixed-breed ponies, and 4 Andalusian-cross horses. For the first 20 weeks, they were all fed hay, ad-libitum. During the next 12 weeks, their hay intake was restricted to 1.25% of body weight.


Obese Standardbred horses lost significant amounts of weight over 20 weeks when fed ad-libitum hay. Their average Henneke Body Condition Score (BCS) improved from 7.2 to 5.3. The pony and Andalusian groups also lost weight, though not as dramatically: average BCS decreased from 8.0 to 7.0. During the next phase when hay was restricted, all groups lost even more weight.  

Implications for your horses

The results of this study reveal that overweight horses and ponies, even breeds known for difficulty with insulin resistance, lose weight when allowed to eat hay ad-libitum (available all day and all night). However, it is likely that these animals would have experienced even more weight loss had several factors been addressed:

  • The study lasted only 20 weeks. There was weight loss, but more time is needed, especially for ponies and insulin resistant horse breeds.
  • The hay had not been analyzed for its sugar and starch content. Had it been confirmed that these horses were consuming hay with ESC + Starch levels less than 10%, the results would likely have been even more favorable.
  • There was no dietary supplementation to alleviate inflammation. Body fat releases inflammatory cytokines which promote more fat storage. Obese horses benefit from dietary addition of omega 3s and antioxidants.
  • The horses were housed and fed individually. The stress of confinement and isolation creates a hormonal response that promotes fat storage.  

During the second phase of the study, where hay was restricted to only 1.25% of body weight, there was greater weight loss. This is to be expected, but at great cost. Forage restriction damages the horse’s ability to maintain a normal weight and subjects him to oxidative stress, causing harm to many tissues and metabolic processes. The researchers do not have a sequel to this study. If they had, they may have found that the animals who endured forage restriction became more severely insulin resistant, as well as developed leptin resistance.


Potter, S.J., Bamford, N.J., Harris, P.A., and Bailey. S.R., 2013. Comparison of weight loss, with or without dietary restriction and exercise, in Standardbreds, Andalusians and mixed breed ponies.Journal of Equine Veterinary Science, 33(5), Abstract, 339.



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