🌾 High-Starch Diets and Horse Reactivity: What Vets Say in 2025 🐎

By Dr Duncan Houston, BVSc

It’s a common belief among horse owners: “Protein makes my horse hot!” But science tells a different story 🧪. In reality, it's not the protein, but energy density—especially from starches—that causes increased excitability and behavioral changes in horses.

🔥 What Do We Mean By “Hot” Horses?

“Hot” behavior in horses typically refers to excessive reactivity, heightened alertness, and sometimes spooky or jittery actions—especially during training or competitions. While this temperament may be desired in certain disciplines, it can pose safety issues and training challenges in others.

In most cases, owners notice these changes after increasing their horse’s grain or feed. But the real culprit isn't protein—it's starch, a high-energy carbohydrate.

🧪 Research: Starch vs. Fiber Diets

A groundbreaking study conducted in England tested the effect of high-starch diets on horse behavior. Eight mature horses were observed over a 28-day period on two different rations:

• 🍞 High-Starch Diet: Grain plus hay
• 🌿 High-Fiber Diet: Hay and alfalfa

After 28 days, the diets were switched and horses were re-evaluated weekly.

💡 The Results Were Striking:

• 📈 Horses on the high-starch diet had significantly higher heart rates during routine handling.
• ⚠️ They showed more disruptions while eating when exposed to unfamiliar stimuli—indicating anxiety or fear.

These findings support what many horse owners already suspect: high-starch meals may lead to overstimulation and anxiety, not simply increased performance or energy.

🌿 Why Horses Thrive on Forage

Horses evolved as continuous grazers, designed to consume small amounts of roughage like grass over 12–16 hours daily. Their digestive systems, particularly the cecum, rely on this slow, steady intake of forage to function optimally. When horses are instead fed large meals twice a day—especially high-starch ones—it disrupts this balance and can lead to:

• ⚡ Gastrointestinal upset
• ⚡ Behavioral swings (“hot” horses)
• ⚡ Colic and laminitis risks

🧈 Fat as a Safer Energy Source

Unlike starch, fat provides slow-release energy and has a calming effect on many horses. It delivers over twice the calories of carbohydrates without spiking insulin or causing digestive stress. Here’s why fat makes sense:

• ✅ No behavioral “highs” or crashes
• ✅ Easier on the gut (less colic risk)
• ✅ Ideal for endurance, dressage, and seniors

Good fat sources for horses include:

• 🥥 Stabilized rice bran
• 🌻 Flaxseed
• 🌽 Corn oil (in moderation)
• 🛢️ Commercial high-fat concentrates

Talk to your veterinarian before switching feeds—especially for insulin-resistant or performance horses. 🧑‍⚕️

🚫 Debunking the Protein Myth

Let’s be clear: protein doesn't make your horse hot. Protein is not a primary energy source. In fact, horses only use protein for energy when carbohydrates and fat are deficient—usually a sign of an unbalanced diet.

While protein is essential for muscle development, skin, and coat health, it won’t trigger anxiety or reactivity. So next time your horse is acting “hot,” take a look at the starch content—not the protein percentage.

💬 Final Thought: Balance Is Everything

In 2025 and beyond, smart equine nutrition isn’t just about feeding more—it’s about feeding right. Feed your horse for their job, body type, age, and temperament. Stick to high-quality forage, limit starch, and consider fat for clean, calm energy. 💪

When in doubt, consult your vet or try AskAVet.com for personalized support. 🩺 Download the Ask A Vet app for 24/7 access to trusted equine advice. 🐴💬

📌 Quick Tips Recap:

• 🌾 Avoid feeding over 5 lbs of grain per meal
• 🐎 Choose hay as the primary feed—fiber is king
• 🧈 Add fat for extra calories—not starch
• 📉 Reduce starch to lower reactivity and stress
• 📱 Use Ask A Vet for nutritional consultations

Article written by Dr Duncan Houston BVSc, equine veterinarian and founder of Ask A Vet.