Perils of Overfeeding Beyond Obesity

An online survey was disseminated to 274 horse owners in the Netherlands to collect information on feeding practices. The survey revealed that many of the horses were overfed energy, protein, and some micronutrients.^* Not only does overfeeding contribute to the obesity epidemic plaguing domesticated horses, but it also influences nutrient leaching and environmental contamination.

Data collected from the survey revealed the following feeding practices:

• Grass (meadow) was the most commonly used preserved forage (77% of survey respondents), followed by alfalfa (43%) or a combination of hay, alfalfa, and haylage;
• Concentrates were offered to almost all horses (94%), and approximately half of those horses were offered more than one type of concentrate;
• Most horses (97%) were fed more than 110% of the crude protein recommended by Nutrient Requirements of Horses, published by the National Research Council;
• Multiple dietary supplements were frequently used (80%), including multivitamins, muscle support, joint protectants, and gastrointestinal aids; and
• Mean starch offered to horses was 2.4 g/kg body weight and sugar intake was 1.4 g/kg body weight, both of which exceed recommended limits for horses sensitive to soluble carbohydrates.

“Multiple feeds and supplements were offered by the owners, and this practice can lead to nutrient duplication and unintended nutrient excesses, as reported in this survey for crude protein and trace minerals,” said Catherine Whitehouse, M.S., a Kentucky Equine Research nutritionist.

For outputs, the calculated nitrogen excretion per horse was 228 g/day, equivalent to almost 8.5 kg of nitrogen per ton of manure. This survey also revealed that copper, zinc, manganese, and cobalt would be excreted in relatively high amounts based on the described diets.

“Oversupplementing beyond the horse’s nutrient requirements can lead to excess levels in the feces and urine that are introduced into the environment. Steps to reduce nutrient excesses include accurately assessing the horse’s activity level, feeding forage and concentrates based on weight not volume, and having forage analyzed for nutrient content, when possible,” advised Whitehouse.

According to the researchers, nutrient losses into the ground surface water cause water pollution and greenhouse gas emissions. They stated, “Precision feeding, which entails precisely meeting the nutrient requirements of animals without exceeding them, offers a viable means of curbing nitrogen inputs” and “to mitigate these concerns, it is crucial to promote sustainable feeding practices and better educate horse owners.”

In sum, the researchers found that horses are often offered too much energy, starch, crude protein, and micronutrients. Reasons for this may include owners overestimating how much forage and feed horses require and overestimating how much exercise horses perform.

“This survey highlighted the importance of proper feeding and manure management practices to support both horse and environmental health. Excess crude protein, phosphorus, and trace minerals can negatively affect the environment; however, these are essential nutrients for the horse and should be provided at adequate levels,” advised Whitehouse.

She added, “Forage-only diets often require supplementation for optimal nutrition, but type and amount of supplement differs based on forage type and amounts and horse class. Some horses may need a vitamin and mineral supplement, whereas other horses benefit from a ration balancer or fortified concentrate when additional calories are needed.”

Learn the differences between a vitamin and mineral supplement, a ration balancer, and a fortified feed.

^*Karasu, G.K., and C.W. Rogers. 2024. Analysis of current equine feeding practices in the Netherlands and identification of potential nutrient leaching and environmental contamination factors. Journal of Equine Veterinary Science 137:105071.