In February 2024, a diet evaluation was requested for a 21-year-old Quarter Horse mare weighing 1700 lb (770 kg) in Alberta, Canada. Reported health concerns included weight gain, poor muscling, low hoof quality, a large hay belly, respiratory issues, insulin resistance, and a history of laminitis.

The horse owner’s primary goal was to support the horse’s digestive and hoof health, with an aim to improve soundness and comfort enough so that she could perform light exercise.

Presentation Prior to Diet Intervention

The mare was assessed and found to have a body condition score of 5.75 out of 9 on the Henneke Scale. She also presented with the following special care needs:

  • Mild insulin resistance
  • Hoof issues related to a previous bout of laminitis
  • Poor muscling
  • Hay belly

The following photo was provided of the mare at the time of evaluation:


Horse History

The mare was housed on limited pasture in the spring and free choice pasture during the summer and fall. Her hay was reported to be low-quality. Pictures of the mare from five months and one year prior to the owner’s request for diet evaluation demonstrated she was slowly losing weight.

Her owner used a weight tape to measure her heart girth and body length and calculated her body weight to be around 1,700 lbs (770 kg). However, the owner noted that this could be an overestimate due to a very large hay belly that she could not seem to resolve.

The owner also noted the mare had persistent hoof pain related to an ongoing laminitic issue that was proving difficult to remedy. This combined with joint and breathing issues limited her ability to exercise.


Laminitis is a painful hoof issue that impacts soundness and ultimately the horse’s ability to exercise. Cases of laminitis can be so severe and painful that horses are unable to walk.

Laminitis typically results from issues with the immune, digestive, and/or endocrine systems.

The three major types of laminitis are: [1][2][3]

  • Endocrinopathic laminitis: the most common form of laminitis is caused by abnormally high insulin in the blood, often due to metabolic dysregulation.
  • Sepsis-associated laminitis: a form a laminitis that occurs secondary to severe, systemic inflammation. It most often occurs due to life-threatening infections, like retained placenta, enterocolitis, and pleuropneumonia.
  • Supporting limb laminitis: the least common form of laminitis is caused by excessive weight bearing on a hoof for a prolonged period of time. Usually this happens because the horse is non-weight bearing on the opposite leg, such as due to an injury.

Combined with the other details of this case, the mare’s difficult history with laminitis suggests endocrinopathic factors were contributing to her overall health concerns.

Hay Belly

Hay bellies in horses are characterized by abdominal distention, giving the horse a rounded appearance that is not related to being overweight. The distention can be related to increased gut fill and gas production that are indicative of impaired digestive function. [4]

Hay bellies often stem from consuming low-quality hay that is difficult for horses to break down in the hindgut. In addition to being higher in fiber content, low-quality hay may also be lower in protein and energy content. [5]

Hay bellies are often accompanied by limited muscling or fat coverage. While the high fiber content of low-quality hay lends to abdominal distention, the low energy content can lead to weight loss and a low protein content can negatively impact muscle maintenance if protein requirements are not met.

The mare’s owner noted that she selected a low-quality hay due to the mare’s weight concerns and limited hay availability in her area.

Weight Issues

The prevalence of obesity in horses may be as high as 27 – 35%. [6] In addition, some breeds such as Quarter Horses may be predisposed to obesity compared to leaner breeds such as Thoroughbreds.