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In November 2024, a diet evaluation was requested for a two-and-a-half year old Dutch Warmblood gelding named Apollo from Michigan, USA.
At the time of his diet evaluation, Apollo was still growing and expected to reach a mature height of at least 17 hh and body weight of approximately 1,300–1,400 lb (590–658 kg).
Apollo’s owner was concerned that his current diet was not fully supporting the demands of growth. He was having difficulty maintaining weight, showed poor muscle development for his age and size, and appeared to have compromised immune function.
The owner’s primary goals were to improve body condition, support healthy muscle growth, and enhance immune health while maintaining a forage-based diet.
Presentation Prior to Diet Intervention
Apollo was described as having difficulty maintaining condition and gaining weight, likely due in part to his large frame and ongoing growth. His owner expressed concerns about his overall body condition, muscle mass, and sensitivity to insect bites and allergies.
The following photo was provided of Apollo from November 2024, prior to his diet evaluation:
Apollo, BeforeHorse History
While it’s normal for young horses to go through lean phases during growth, Apollo’s owner noted he consistently appeared on the leaner side and did not seem to fill out between growth spurts as expected.
Apollo was also described as a very sensitive horse, with noticeable reactions to insect bites and seasonal allergies. His owner shared concerns that his immune health may have been impacted by the loss of his dam at two months of age, as he was raised as an orphan foal.
Prior to the diet evaluation, his owner had tried bovine colostrum and AniMed’s AniHist H for additional immune support, but did not see a noticeable improvement in Apollo’s sensitivity.
What's your top priority with your horse's health?
What's your top priority with your horse's health?
Feeding Growing Horses
At 2.5 years of age, horses are nearing maturity but are still undergoing important growth and development. [1] While their growth rate has slowed, their diet needs to provide adequate energy, high-quality protein, and balanced vitamins and minerals to support continued musculoskeletal development.
A body condition score of 4–5 on the Henneke Scale is recommended during this age. This is typically achieved with good-quality forage, appropriate protein sources, and a well-balanced vitamin and mineral supplement. Owners can build diets around forage with targeted supplementation, rather than relying solely on complete feeds.
In addition to meeting basic nutrient requirements, it’s important to manage total energy intake, particularly from sugar and starch (hydrolyzable carbohydrates; HC). Studies show excess energy intake is associated with with increased risk of developmental orthopedic diseases (DOD), including osteochondrosis lesions and abnormalities in growth plates. [2]
Higher intakes of sugar and starch may also influence hormonal balance, which can affect normal bone and cartilage development and potentially increase DOD risk. [3] It’s important to note that multiple factors influence DOD risk, including genetics, growth rate, and nutrition. Some horses may tolerate higher energy intake without issue, while others may be more sensitive.
In Apollo’s case, there were no signs of developmental orthopedic disease at the time of dietary intervention. However, because he was still in ongoing musculoskeletal development, dietary changes to support weight gain were made conservatively.
The goal was to increase calorie intake in a controlled manner while limiting excess sugar and starch, helping support healthy weight gain without unnecessarily increasing nutritional risk factors associated with DOD.
Weight Issues
Difficulty maintaining weight in growing horses can result from a variety of health and dietary factors, including:
- Limited forage availability
- Poor-quality forage
- Insufficient energy (calories) or protein
- Digestive disorders
- Underlying medical conditions
As continuous grazers, horses benefit from consistent access to forage. Increasing forage quantity or improving forage quality is often the most effective and economical way to support weight gain. When forage intake is already optimized, owners can introduce additional calories through energy-dense feeds.
Owners should avoid feeding diets high in sugar and starch, as they can negatively impact digestive health and further hinder weight gain. [4][5][6]
For most horses, nutritionists recommended keeping hydrolyzable carbohydrates (HC; sugar and starch) below 12% of the total diet on a dry matter basis. In some cases, such as performance horses, higher HC levels may be appropriate to meet energy demands.
Conversely, horses with metabolic concerns may benefit from further restricting HC to 10% or less.
Fiber- and fat-based energy sources are preferred to safely increase calorie intake in horses. Options such as beet pulp and alfalfa provide highly digestible fiber, while fat sources like oils or flaxseed offer concentrated calories without increasing sugar and starch intake.
When adjusting calorie intake in growing horses, it’s important to ensure the diet continues to meet protein requirements. In Apollo’s case, increasing his alfalfa intake helped boost his protein intake while also providing additional calories from highly digestible fiber.
Immune Health
Allergies in horses are complex immune disorders influenced by both genetic and environmental factors. While not all horses respond to the same allergens, research suggests that genetics play a role in allergic sensitivity. [7]
Allergic reactions occur when the immune system overreacts to otherwise harmless substances such as insects, pollen, mold, dust, feed ingredients, or topical products. This response can lead to signs such as itching, skin irritation, coughing, or nasal discharge.
One of the most common allergic conditions in horses is insect bite hypersensitivity (IBH), also known as sweet itch or summer eczema. This condition is primarily caused by a type I hypersensitivity reaction to the saliva of biting insects, most commonly Culicoides midges, but also mosquitoes, black flies, and stable flies. [8][9][10][11]
The allergic response involves the production of allergen-specific IgE antibodies, which trigger the release of inflammatory compounds such as histamine from mast cells. This is what causes the intense itching associated with the condition. [12]
Sweet itch often follows a seasonal pattern, with flare-ups during warmer months when insect activity is highest, although symptoms may persist year-round in some climates. Affected horses may develop hair loss, skin lesions, and areas of irritation (most commonly along the mane, tail, and back). Horses with skin irritation often rub excessively, leading to further inflammation and potential secondary infections. [8][9]
There is no cure for sweet itch, but symptoms are typically managed through a combination of environmental control, medical support, and nutritional strategies. Reducing insect exposure is key, and may involve a combination of anti-fly apparel, topical insecticides, and turnout timing.
Nutritional support can also play a role in maintaining healthy skin and immune function. Key nutrients such as omega-3 fatty acids, zinc, and vitamin E help support skin integrity, antioxidant defenses, and normal immune responses. Certain functional ingredients may also help maintain a healthy inflammatory balance. [13][14]
In Apollo’s case, a more comprehensive vitamin and mineral supplement was recommended to help support optimal immune function and overall health.
Initial Diet
At the time of the nutrition consultation, Apollo’s daily ration consisted of:
- Free-choice access to locally grown hay & pasture
- 3 lb (1.4 kg) – CoolStance Copra
- 1 lb (0.5 kg) – Golden Ground Flax (Triple Crown)
- 5 lb (2.3 kg) – Alfalfa Pellets
- 6 g – MagRestore
- 4 oz (125 g) – Vermont Blend
- 2,000 IU (14 g) – Elevate Maintenance Powder
Overall, the diet appeared to provide adequate energy and protein, despite Apollo’s challenges with maintaining weight during growth. Vitamin and mineral levels were generally sufficient, except for iodine, vitamin A, and vitamin D. Based on estimated values, the hydrolyzable carbohydrate (HC; sugar and starch) content was approximately 9%.
Intervention
As part of the nutrition consultation, an updated diet plan was proposed to address the specific concerns of Apollo’s diet.
Table 1. Summary of Diet Intervention
| Horse Issue | Nutrition Goal | Intervention | Notes |
|---|---|---|---|
| Body Condition | Improve body condition | Increased alfalfa pellets | Increases calorie and protein intake |
| Muscle Health | Support muscle growth | Added AminoTrace+, removed VT blend | Provides additional amino acid support |
| Immune Issues | Support immune function | Added AminoTrace+ | Provides more comprehensive vitamin and mineral coverage |
The recommended dietary changes were intended to support Apollo’s body condition, muscle development, and overall health by increasing the calorie density of the diet and providing more comprehensive amino acid, vitamin, and mineral support.
These adjustments were designed to help address ongoing concerns with condition and growth while supporting long-term immune and metabolic function.
Balancing the Diet
The dietary adjustments were designed to increase the calorie density of Apollo’s diet to support improved body condition and promote healthy, sustained growth. While his initial diet met energy and protein requirements, muscle development and overall condition remained areas of concern.
To address these issues, the diet was modified to increase his energy and protein requirements by increasing the quantity of alfalfa pellets.
Replacing VT blend with AminoTrace+ provided enhanced levels of essential amino acids along with more comprehensive vitamin and mineral coverage, helping to better meet his nutritional needs and support immune function.
Updated Diet
After the consultation, Apollo’s owner implemented the following dietary adjustments. His updated daily diet consisted of:
- Free-choice access to locally grown hay & pasture
- 1 lb (0.5 kg) – Golden Ground Flax (Triple Crown)
- 10 lb (4.5 kg) – Alfalfa Pellets
- 250 g – AminoTrace+
- 1 tablespoon – salt
In addition, the owner elected to add 3 g of Magnesium glycinate, 2 scoops (130 g) Digestive HP (Poseidon), and 1 scoop (15 g) Lifespan (Equine Veterinary Essentials) at her own discretion.
Outcome
Overall, the dietary adjustments led to a notable improvement in body condition and muscle development. Apollo’s owner reported visible changes within one month of implementing the new plan, with continued progress observed at the three-month mark.
The following photos highlight the differences in his condition at one and three months post-intervention:
Apollo, One Month
Apollo, Three Month
Apollo, Three Month
Now, at nearly 4 years old, Apollo has made significant strides in his overall condition. However, he continues to show sensitivity to allergies and insects, which may benefit from further evaluation to explore more targeted support strategies.
Apollo, March 2026
Apollo, March 2026Discussion
Young, growing horses like Apollo have elevated nutrient requirements to support steady growth, muscle development, and immune function. It is not uncommon for horses with larger frames or rapid growth patterns to appear lean or have difficulty maintaining body condition, particularly if calorie intake does not fully meet their needs.
In Apollo’s case, his initial diet met energy and protein requirements on paper, but his body condition and muscle development suggested that nutrient utilization and overall dietary balance could be further optimized.
Additionally, his history as an orphan foal and ongoing sensitivity to insects and allergens highlighted the importance of supporting immune function alongside growth.
The updated feeding program focused on increasing calorie density while maintaining a forage-based approach and ensuring balanced vitamin and mineral intake. Increasing alfalfa intake helped provide additional calories from highly digestible fiber while also supporting protein intake for muscle development.
The switch to AminoTrace+ further supported essential amino acid intake and provided more comprehensive micronutrient coverage to promote immune health.
Care was also taken to avoid excessive sugar and starch intake, as higher hydrolyzable carbohydrate (HC) levels can negatively impact digestive health and are not necessary for supporting weight gain in most growing horses.
“Now that we have been using Mad Barn products for over a year, I feel they have made such a huge difference!”
— Feedback From OwnerFollowing these adjustments, Apollo showed notable improvements in body condition and topline within the first month, with continued progress over the following months.
This case highlights the importance of looking beyond basic nutrient adequacy and considering factors such as amino acid balance, calorie source, and micronutrient support when addressing growth, body condition, and overall health in young horses.
References
- Nutrient Requirements of Horses: Sixth Revised Edition. Washington, DC: The National Academies Press. 2007. View Summary
- Juliand. V. and Martin-Rosset. W. W., Eds. Nutrition of the Performance Horse. Wageningen Academic. 2004.
- Geor. R. J. et al. Equine Applied and Clinical Nutrition: Health, Welfare and Performance. Saunders Elsevier. 2013.
- Raspa. F. et al. A high-starch vs. high-fibre diet: effects on the gut environment of the different intestinal compartments of the horse digestive tract. BMC Veterinary Research. 2022. View Summary
- Colombino. E. et al. Gut health of horses: effects of high fibre vs high starch diet on histological and morphometrical parameters. MC Veterinary Research. 2022. View Summary
- Raspa. F. et al. Microbiota characterization throughout the digestive tract of horses fed a high-fiber vs. a high-starch diet. Frontiers in Veterinary Science. 2024. View Summary
- Meulenbroeks. C. et al. Allergen-Specific Cytokine Polarization Protects Shetland Ponies against Culicoides obsoletus-Induced Insect Bite Hypersensitivity. PLoS ONE. 2015. View Summary
- van den Boom. R. et al. The effect of a supplement containing sunflower oil, vitamins, amino acids, and peptides on the severity of symptoms in horses suffering insect bite hypersensitivity. Tijdschrift voor Diergeneeskunde. 2010. View Summary
- Cox. A. and Stewart. A. J. Insect Bite Hypersensitivity in Horses: Causes, Diagnosis, Scoring and New Therapies. Animals. 2023;13(15):2514. View Summary
- Lanz. S. et al. Insect Bite Hypersensitivity in Horses is Associated with Airway Hyperreactivity. Journal of Veterinary Internal Medicine. 2017;31(6):1877–1883. View Summary
- Jonsdottir. S. et al. Comparison of recombinant Culicoides allergens produced in different expression systems for IgE serology of insect bite hypersensitivity in horses of different origins. Veterinary Immunology and Immunopathology. 2021. View Summary
- Jonsdottir. S. et al. New Strategies for Prevention and Treatment of Insect Bite Hypersensitivity in Horses. Current Dermatology Reports. 2019.
- O'Neill. W. et al. Flaxseed (Linum usitatissimum) supplementation associated with reduced skin test lesional area in horses with Culicoides hypersensitivity. Can J Vet Res. 2002. View Summary
- Baalsrud. K. et al. Influence of vitamin E and selenium supplement on antibody production in horses. Equine Vet J. 1986. View Summary
