By Juliet M. Getty, PhD

Researchers from the University of Melbourne, Australia, and the WALTHAM Centre for Pet Nutrition in the United Kingdom examined[i] 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: four Standardbreds, four mixed-breed ponies and four 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, although 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.[ii]

Juliet M. Getty, PhD, is an independent equine nutritionist with a wide U.S. and international following. Her research-based approach optimizes equine health by aligning physiology and instincts with correct feeding and nutrition practices.


[i] Study: 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.

[ii] Please read two articles in Dr. Juliet Getty’s library:

1) Restricting Forage is Incredibly Stressful – Choose a different method to help your horse lose weight

2) Can the Damaged Insulin Resistant Horse be Fixed?