Case Study: Topline and Metabolic Health Improvement in a 12-Year-Old Mare

In December 2024, a diet evaluation was requested for a 12-year-old Morgan mare named Kelta. She weighed approximately 800 lb (363 kg) and was located in Alaska, USA. The initial concerns reported included topline loss, metabolic health, and weight issues.

The owner’s primary goal was to support her topline health, as Kelta had experienced a significant decline in muscle mass in recent months.

Presentation Prior to Diet Intervention

Kelta was listed at an ideal weight and in light exercise at the time of her diet evaluation. She presented with the following special care needs:

• Loss of topline muscling
• Risk of metabolic health issues
• History of obesity

The following photo was provided of Kelta in December 2024, prior to her diet evaluation:

Kelta, Dec 2024

Horse History

At the time of her diet evaluation, Kelta was lightly exercised once or twice a week, consistent with her typical reduced workload during the winter months. However, unlike in previous years, her owner observed a noticeable and unusually rapid loss of muscle along her topline as her workload decreased.

The decline was most evident around her withers and the top of her croup, raising concern that her current diet might not adequately support muscle maintenance.

In Kelta’s case, her mixed brome hay appeared to provide sufficient protein for muscle maintenance. Key antioxidants, including vitamin E and selenium, were also present at appropriate levels in her diet.

Topline Loss

Muscle tissue, including the muscles along the topline, is composed primarily of proteins. For horses to build and maintain muscle, their diet must supply enough protein along with the right balance of amino acids.

Even though crude protein levels in Kelta’s diet appeared sufficient, supplementing essential amino acids was recommended to help optimize muscle maintenance and restore topline health.

Proteins are chains of amino acids, which the body requires to effectively build and repair muscle tissue. For most horses, forage is the primary source of dietary protein and amino acids. However, not all forages provide an optimal balance of essential amino acids, which horses cannot synthesize on their own. ^[1][2]

The most critical limiting amino acids for horses are lysine, methionine, and threonine. These must be supplied in sufficient amounts for the horse to effectively synthesize muscle proteins. If any are deficient, the body’s ability to utilize dietary protein is reduced, hindering muscle maintenance and development regardless of total protein intake. ^[3][4]

In horses, lysine is the first limiting amino acid, meaning it is most commonly deficient in typical diets. Methionine deficiency is also an emerging concern, as low sulfur levels in soil can reduce methionine content in some forages. ^[5]

Metabolic Health

Morgan horses, like Kelta, are prone to metabolic concerns and issues with weight management. Since Kelta had a history of obesity, her owner was proactive in supporting her metabolic health by feeding a low-hydrolyzable carbohydrate (HC; sugar + starch) diet and carefully maintaining an appropriate body weight.

Equine Metabolic Syndrome (EMS) is a metabolic disorder that affects how horses process dietary sugars and convert them into energy. It is especially common in easy keeper breeds, who are naturally predisposed to weight gain. ^[6]

EMS is characterized by insulin dysregulation, which means the horse’s body becomes less responsive to insulin. In horses with EMS, excess body fat can lead to increased fat accumulation in the liver, which can interfere with insulin signaling and contribute to insulin resistance. ^[7]

Common signs of EMS include: ^[8]

• Generalized obesity or difficulty losing weight
• Abnormal fat deposits, such as a cresty neck or fat pads around the tailhead
• Increased risk of laminitis

Management of EMS focuses on improving insulin sensitivity and reducing the risk of laminitis. This typically includes: ^[9]

• Feeding a diet low in hydrolyzable carbohydrates (HC; starches and sugars)
• Reducing total caloric intake to promote weight loss
• Encouraging regular exercise
• In some cases, using medication to improve insulin regulation

For horses with EMS, forage should be analyzed to determine its hydrolyzable carbohydrate content. Diets high in HC can worsen insulin resistance and contribute to metabolic complications. To reduce this risk, forage should contain less than 10% HC on a dry matter basis. ^[10]

Horses with EMS should also be evaluated for Pituitary Pars Intermedia Dysfunction (PPID), also known as Cushing’s disease. PPID can worsen insulin resistance and often presents with symptoms like muscle wasting, topline loss, and a long, curly coat.

While PPID is more common in horses over 15, this condition can occur in younger horses as well. ^[11]

Weight Issues

Given Kelta’s history of obesity and her breed’s predisposition to weight gain, it was important to support topline and muscle maintenance while carefully managing calorie intake.

In North America, an estimated 51% of horses are overweight, with up to 8% classified as obese. ^[7][12][13]

Excess weight commonly develops when calorie intake exceeds energy expenditure, particularly in horses with limited exercise. Factors such as age and activity level influence a horse’s energy requirements, and some horses are naturally more prone to weight gain than others. ^[14]

Body Condition Scoring (BCS) is widely used to evaluate a horse’s weight status, with scores of 7 or higher indicating excess body fat. Effective weight management typically involves reducing caloric intake, increasing physical activity, and adjusting the diet to support long-term metabolic health.

Initial Diet

At the time of Kelta’s initial nutrition consultation in December, her daily ration consisted of:

• 20 lb of tested Brome mix hay
• 4 oz of California Trace Plus

The mixed brome hay fed to Kelta was analyzed for nutrient composition, with the results shown below:

Table 1. Nutrient analysis of original brome hay (dry matter basis)

Overall, the initial diet appeared to provide adequate energy, protein, and many essential vitamins and minerals. The main deficiency present in the diet was sodium.

The HC (sugar and starch) content of the diet was appropriate for a metabolic horse at 8.3% on a dry matter basis.

A month after the initial diet recommendations, Kelta’s owner requested a second diet evaluation. Based on the initial recommendations, she had implemented Mad Barn’s w-3 Oil, alfalfa pellets, an amino acid supplement, and salt.

Her owner also included an updated hay analysis for a new batch of hay, which supplied lower protein content than the previous brome mix.

Kelta’s daily ration at the time of her second diet evaluation consisted of:

• 20 lb of tested Brome mix hay
• 6 lb of Alfalfa pellets
• 4 oz of California Trace Plus
• 1 oz of salt
• 3 oz of w-3 Oil
• 2 oz of Regen-X

The hay analysis for the second batch of mixed brome hay fed to Kelta is shown below.

Table 2. Nutrient analysis of new brome hay (dry matter basis)

With these changes, the updated diet now met Kelta’s sodium requirements and supplied higher levels of essential amino acids, vitamin E, and omega-3 fatty acids.

Because the new hay tested at a lower protein content than the previous hay, her owner proactively added alfalfa pellets to help maintain protein levels in the diet.

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Intervention

Following both consultations, updated diets were proposed to address Kelta’s concerns related to her recent muscle loss.

Table 3. Summary of Diet Intervention

These additions were recommended to support Kelta’s topline muscles by ensuring adequate amino acid intake and by providing general muscle health support.

Balancing the Diet

The primary goal of the dietary adjustments was to address Kelta’s muscle wasting by supplying essential amino acids that are often deficient in forage.

To simplify her supplementation program, Kelta’s owner replaced California Trace Plus and Regen-X with Mad Barn’s AminoTrace+, an enhanced vitamin and mineral supplement.

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• Supports metabolic health
• Formulated for IR/Cushing's
• Supports hoof growth

AminoTrace+ helped ensure Kelta’s overall nutrient requirements were met while providing higher levels of amino acids compared to her previous supplements. It also offers continued support for her predisposition to metabolic disorders.

In addition, W-3 Oil was introduced to supply natural vitamin E and the omega-3 fatty acid DHA, both of which play key roles in muscle function and exercise recovery.

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Updated Diet

After implementing the recommended changes and seeing improvements in topline musculature, Kelta’s owner simplified her diet to maintain these results.

Kelta’s most recent daily ration consisted of:

• 20 lb of Brome Mix Hay
• 4 lb of Alfalfa pellets
• 200 g of AminoTrace+
• 1 oz of salt
• 3 oz of w-3 Oil

With these dietary adjustments, Kelta’s topline muscle was restored, and she continued to maintain a healthy weight and metabolic status.

Outcome

Within one month of the final dietary adjustments, Kelta showed noticeable improvement in her topline musculature. Despite the transition to hay with a lower crude protein content, her topline continued to develop.

By the two-month mark, her owner was able to simplify her feeding program while maintaining both muscle and overall body condition.

The following photos illustrate the changes in her condition two months after the diet adjustments:

Kelta, Jan 2025

Kelta, Feb 2025

Kelta, Feb 2025

Kelta, Feb 2025

Discussion

In Kelta’s case, adding essential amino acids resulted in a noticeable improvement in topline health within two months. This outcome highlights the importance of not only meeting overall protein requirements but also ensuring the diet supplies a balanced amino acid profile.

Even when crude protein intake appears sufficient, deficiencies in limiting amino acids such as lysine, methionine, and threonine can reduce a horse’s ability to maintain or rebuild muscle.

Targeted supplementation can therefore be a simple but highly effective strategy for supporting muscle development and overall condition, particularly during seasonal changes or shifts in forage quality.

Kelta’s owner says, “I couldn’t figure out why my mare — only 12 years old and never sickly in her life — was suddenly deteriorating. Thank you so much for helping me understand what she was lacking and how to feed her properly to restore her topline.”