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. [7]

Estimates of the mare’s weight consistently suggested she was overweight, although the owner noted that the hay belly likely skewed interpretation of her condition, and that she was also rather under muscled.

In addition, pictures provided of the mare one year and five months prior to submission suggested that she was gradually losing weight despite the persistence of her hay belly.


A combination of factors made managing body condition difficult for this mare, including:

  • Apparent digestive and metabolic dysfunction
  • Limited hay availability in the area
  • Difficulty estimating actual weight due to persistent hay belly

Hoof, Mane, Tail, and Coat Health

Deficiencies in nutrients such as zinc and copper are associated with reduced hoof and coat quality. [8][9] Other nutrients such as biotin, amino acids, and vitamin E are also important for supporting hoof, skin, coat, and hair health as they contribute to keratin and collagen synthesis, and may protect from UV damage to hair and skin. [10][11][12]

Before dietary changes were made, the mare was noted to have issues with hoof health such as weakness and brittleness, and fluctuations in shape and strength.

The mare’s owner mentioned that the mare looked to be a dark chestnut color. However, in the summer while she had access to pasture, she noted dark marks over each of her eyes. Upon closer inspection, the owner realized that she was in fact a red dun with a very faded coat pattern.

In addition, the mare struggled with mane and tail health. Her tail had never been longer than hock-length, and her mane was easily tangled and rough in texture.

Initial Diet

At the time of the nutrition consultation, the horse’s daily ration consisted only of free-choice low-quality grass hay. This diet was put in place to minimize calorie intake due to metabolic concerns.

No forage sample was available, so the diet evaluation conducted was based on an average low-quality hay profile, which suggested deficiencies in several key nutrients such as:

  • Zinc
  • Copper
  • Selenium
  • Vitamin E
  • Sodium

In addition, the diet was likely lacking in biotin, providing significantly less than the recommended 15 – 20 mg per day. [13]

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As part of the consultation, an updated diet plan was formulated to address the specific concerns of the horse.


Table 1. Summary of Diet Intervention

Horse Issue Nutrition Goal Intervention Notes
Slightly overweight Weight Loss Decrease caloric intake by rationing hay intake to 24 lbs (11 kg) per day Improves body condition
Persistent hay belly Digestive support Added Optimum Digestive Health Targeted support for hindgut health
Low hoof and coat quality Meet vitamin and mineral requirements Added AminoTrace+ and salt Provide highly available trace minerals and natural vitamin E


Due to limited hay availability in the region, the mare’s forage source was not changed, but hay was rationed to reduce available calories and encourage weight loss.

Forages are typically a good source of fiber, energy, and protein, but they do not fully meet a horse’s requirements for micronutrients including copper, zinc and vitamin E. [14] To balance the diet, Mad Barn’s AminoTrace+ was added as a concentrated source of vitamins and minerals.

In addition to balancing the vitamin and mineral profile of the diet, AminoTrace+ provides a rich source of antioxidants and amino acids to support horses with metabolic issues such as insulin resistance.

One tablespoon of salt was also added to the diet to meet the mare’s sodium requirement and encourage hydration.


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  • Complete mineral balance
  • Supports metabolic health
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  • Hoof growth

Gut Health

To support hindgut health and forage fermentation, Mad Barn’s Optimum Digestive Health is a source of beneficial probiotics, prebiotics, yeast and digestive enzymes.

Poor digestibility of forage can contribute to the development of a hay belly. In addition to impaired fiber breakdown, low-quality hay may lead to reduced absorption of other nutrients such as protein.

In this case, low-quality forage likely contributed to the horse’s digestive symptoms and difficulty maintaining muscle mass.

Adding Optimum Digestive Health to the diet helped to support the mare’s hindgut function maintain a healthy gut microbiome, improve feed efficiency and support nutrient absorption.

Optimum Probiotic

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  • 20 billion CFUs per serving
  • Pure probiotic with no fillers
  • Blend of 5 beneficial strains
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Balancing the Diet

While the primary focus was the mare’s weight and digestive issues, it was equally important to rebalance the diet to supply adequate vitamins and minerals for muscle, hoof, coat, and overall health.

Feeding AminoTrace+ helped to ensure the mare’s vitamin and mineral requirements were met and address concerns related to nutritional deficiencies.

Updated Diet

Following consultation, the horse’s updated daily diet consisted of:

  • 24 lbs (11 kg) of hay
  • 2.25 scoops (225 grams) of AminoTrace+
  • 1.5 scoops (120 grams) of Optimum Digestive Health
  • 1 tablespoon of plain loose salt


Overall, the dietary adjustments led to significant improvements: the mare continued to lose weight, developed a healthier, shinier coat, exhibited improved energy levels, and saw improvement with her hay belly.

Very detailed evaluation for both of my horses. I have followed the recommended diet and have noticed an improvement in body condition and overall health.
- Review Provided by Horse Owner

Within two months of implementing the dietary changes, the mare’s hay belly began to lessen, and her owner noted that she was less gassy, less sensitive around the flanks, and more energetic.

Additional reported improvements included the following:

  • Her body condition continued to improve at a healthy rate
  • Her hooves improved in shape and strength, and she was better able to stand on three feet for farrier care
  • Her coat color changed from a dull, dark chestnut color to reveal that she was a red dun
  • Her mane and tail growth increased substantially, with her tail finally growing below the level of the hocks

The following photos show side, dorsal and tail views of the horse after diet evaluation:


Many horses have difficulty maintaining a healthy body condition. Given that the mare in this case study was a Quarter Horse with insulin resistance issues, her difficulty losing weight and maintaining a normal body condition was not out of the ordinary.

Since the horse was overweight, maintaining a low caloric intake while meeting vitamin and mineral requirements was a priority for the updated feeding program. However, due to the horse’s suspected digestive and metabolic issues, it was important to provide additional supportive care without significantly increasing calories.

The rationing of hay, addition of AminoTrace+ and salt to meet vitamin and mineral requirements, and addition of Optimum Digestive Health helped to strike a balance between managing weight, meeting nutrient needs, and supporting digestive health while on a low-quality hay.

Addressing nutritional deficiencies led to noticeable improvements in hoof, coat, mane, and tail health, and ultimately improved soundness. This allowed the potential to return to light work to further support weight loss and muscle development.

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  1. Patterson-Kane, J. C. et al., Paradigm Shifts in Understanding Equine Laminitis. The Veterinary Journal. 2018. View Summary
  2. van Eps, A., Sepsis-Related Laminitis: Prevention in the Horse at Risk and Treatment of the Ongoing Case. American Association of Equine Practitioners. 2017.
  3. Belknap, J. K. and Geor, R. J., Eds., Equine Laminitis. 1st ed. Wiley Blackwell, Ames, Iowa. 2017.
  4. Santos, A. S. et al., Understanding the Equine Cecum-Colon Ecosystem: Current Knowledge and Future Perspectives. Animal. 2011. View Summary
  5. Kohn, R. A. and Allen, M. S., Effect of Plant Maturity and Preservation Method on In Vitro Protein Degradation of Forages. Journal of Dairy Science. 1995.
  6. Giles, S. L. et al., Obesity Prevalence and Associated Risk Factors in Outdoor Living Domestic Horses and Ponies. PeerJ. 2014.
  7. Pratt-Phillips, S. E. et al., Assessment of Resting Insulin and Leptin Concentrations and Their Association With Managerial and Innate Factors in Horses. Journal of Equine Veterinary Science. 2010.
  8. Marycz, K. et al., The Correlation of Elemental Composition and Morphological Properties of the Horse’s Hair after 110 Days of Feeding with High Quality Commercial Food Enriched with Zn and Cu Organic Forms. Electronic Journal of Polish Agricultural Universities. 2009.
  9. Higami, A., Occurrence of White Line Disease in Performance Horses Fed on Low-Zinc and Low-Copper Diets. Journal of Equine Science. 1999.
  10. Buffa, E. A. et al., Effect of Dietary Biotin Supplement on Equine Hoof Horn Growth Rate and Hardness. Equine Veterinary Journal. 1992. View Summary
  11. McKittrick, J. et al., The Structure, Functions, and Mechanical Properties of Keratin. JOM. 2012.
  12. Keen, M. and Hassan, I., Vitamin E in Dermatology. Indian Dermatology Online Journal. 2016.
  13. National Research Council, Nutrient Requirements of Horses: Sixth Revised Edition. The National Academies Press, Washington, DC.
  14. Richards, N. et al., Nutritional and Non-Nutritional Aspects of Forage. Veterinary Clinics of North America: Equine Practice. 2021. [MB-REF URL=””]