In May 2024, a diet evaluation was requested for Phix, an eleven-month-old appaloosa gelding in Nova Scotia, Canada. At the time of the submission, he weighed approximately 550 lb (250 kg). Phix was reported to be healthy but slightly underweight.

The horse owner’s primary goal was to encourage weight gain to achieve a healthy body condition score.

Presentation Prior to Diet Intervention

Phix was described as slightly underweight in his submission, a description which the owner and the horse’s veterinarian agreed on.

He also had other environmental changes worth considering. At the time of submission, he had been recently castrated and was being hand walked often to minimize swelling and encourage drainage while he recovered from this routine surgery. .

The following photos were provided of the gelding from May 2024:

Horse History

At the time of submission, Phix measured 14.5 hh tall, and was estimated to have a body condition score of 3.75 on the 9-point Henneke scale.

He was provided free choice access to hay and pasture. In addition, he was fed sixteen cups of Purina Evolution Juvenile spread over three meals throughout the day.

Forage analyses were not available, so nutrient intake estimates were made using average quality grass hay and pasture for his geographic region.

Feeding Growing Horses

Growing horses typically reach around 60% of their mature body weight by 11 months old. [1] While their growth rate is declining at this stage, they still require an energy- and protein-dense diet to support healthy growth and development.

In addition to meeting protein and energy requirements, growing horses also require sufficient mineral and vitamin intake from the diet.

The ideal body condition score for a growing horse is 4 to 5 on the Henneke Scale. This can be achieved by providing high-quality forage and protein sources, as well as vitamin and mineral supplementation.

Complete feeds designed for growing horses are commonly used to achieve these goals, although energy and protein sources such as alfalfa, soybean meal, and oil can also be fed alongside a complete vitamin and mineral supplement to meet growing horses’ dietary needs.

Once basic nutrient requirements are met, there are additional aspects to consider when balancing the diet for a growing horse. Avoiding excessive energy, sugar, and starch intakes can help prevent issues with normal musculoskeletal development and growth.

Developmental orthopedic diseases (DODs) are a group of conditions related to abnormal cartilage, bone, or soft tissue development. Genetics, growth rate, and nutrition can impact the likelihood of DOD development. While each of these factors alone may not lead to the development of DODs on their own, it is likely that a combination of factors leads to disease development.

For example, some horses may tolerate a relatively high energy intake without developing DODs, while those with a genetic predisposition to DODs may not fare as well.

Additionally, while some horses may tolerate a high-calorie intake when the calories come from protein or fat, an excess intake of sugar and starch (hydrolyzable carbohydrates or HC) can have a more negative impact.

Feeding excess energy may contribute to rapid growth that predisposes foals to DODs. Several studies have shown an association between excess energy intake and the presence of osteochondrosis dissecans lesions, conformation abnormalities, and disturbances in growth plates. [2]

In addition, high sugar and starch intakes can affect hormonal balance, which can in turn affect the development of bone and cartilage. Thus, high sugar and starch intakes may contribute to hormonal alterations that increase the risk of DODs. [3]

In Phix’s case, there were no indications of developmental orthopedic disease at the time of dietary intervention. However, when reformulating the diet to encourage weight gain, it was important to provide a moderate energy intake while limiting sugar and starch consumption.

Feeding Underweight Horses

Weight loss can occur in horses due to a number of health and dietary factors, including:

  • Lack of forage availability
  • Low quality forage
  • Digestive disorders
  • Other underlying medical conditions

Horses are continuous grazers, so increasing their forage quantity or quality is often the easiest and most affordable way to encourage weight gain. In cases where forage intake is already maximized and quality is sufficient, additional calories can be added in the form of energy-dense feeds.

Diets with excessive sugar and starch should be avoided, as these diets can cause digestive issues that further hinder weight gain. [4][5][6]

For most horses, it’s recommended to keep the HC content under 12% of the diet on a dry matter basis. In some cases, feeding higher HC intake may be appropriate, such as for horses that need more energy to fuel performance. Conversely, some horses benefit from having HC further restricted to 10% or less of the diet to support metabolic health.

As an alternative to sugar and starch, calories from fiber- and fat-rich sources are recommended to increase calorie intake. Fiber-based feeds such as beet pulp and alfalfa, or fat sources like oils or flax provide highly digestible fiber and fat to increase calorie intake.

When adjusting the calorie intake of growing horses, ensure that protein requirements are still met. If concentrate feeds are reduced to control HC levels, alfalfa can be added to maintain protein intake and supply calories from highly digestible fiber.

In the present case, Phix had been evaluated thoroughly by a veterinarian with no indication that digestive or other health issues were contributing to his condition. However, the HC content of his diet was slightly elevated.