Vet Insights: Understanding Weight Loss in Foals 2025 🐴🍼

By Dr Duncan Houston, BVSc

Watching a foal grow should be a joyful experience—but when weight gain stalls or a young horse begins to lose condition, it’s a cause for concern. Many foals grow well for the first few months, only to show unexpected weight loss around three months of age. Understanding the reasons behind this trend is key to early intervention and long-term health. 🧠🐎

In this 2025 veterinary guide, Dr Duncan Houston explains the common causes of weight loss in foals, how to prevent and manage these problems, and how to accurately assess a foal’s body condition. 💡🩺

1. When and Why Weight Loss Happens in Foals 🕒

Most foals grow rapidly during the first few months of life. By 3 months of age, they may begin transitioning from milk to solid feed and forage. It’s during this transitional phase that weight gain may slow or even reverse. 📉

Key triggers include:

• 🪱 Parasites (especially roundworms)
• 🦠 Gastrointestinal infections
• 💨 Respiratory illness (e.g., Rhodococcus)
• 🍽️ Nutritional deficiencies or poor milk supply

2. Roundworms: The Most Common Cause 🪱

Roundworms (Parascaris equorum) are the #1 cause of weight loss in foals. These parasites can cause:

• 📉 Poor growth or sudden weight loss
• 💩 Pot-bellied appearance
• 🥱 Lethargy and dull coat
• ⚠️ Potential for colic if loads are heavy

🔄 Deworming Protocol

• Start at 2 months of age
• Repeat every month until 6 months
• Use fenbendazole or pyrantel—avoid ivermectin early on (not effective vs. roundworms)

Be cautious with high parasite loads—sudden deworming can cause impaction colic. Always consult your vet on best protocols. 🧪

3. Digestive Infections: Hidden Dangers 🦠

Foals are vulnerable to several gastrointestinal pathogens. These can cause diarrhea, colic, and malabsorption. Key culprits include:

• 💩 Clostridium spp. – often severe, sometimes bloody diarrhea
• 🦠 Salmonella – zoonotic, causes fever, diarrhea, lethargy
• 🧫 E. coli – can lead to sepsis in neonates
• 🔍 Lawsonia intracellularis – causes proliferative enteropathy

🔬 Lawsonia Insights

Lawsonia infections can be especially tricky. These foals may:

• ⚖️ Lose weight without diarrhea
• 🩹 Show fluid swelling in the lower legs
• 🤕 Appear intermittently colicky

Diagnosis is made via PCR, ultrasound, or bloodwork, and treatment involves specific antibiotics and nutritional support. 📈

4. Respiratory Infections & Rhodococcus equi 💨

Rhodococcus equi is a common cause of pneumonia in foals aged 1–6 months. Symptoms include:

• 🌡️ Fever and lethargy
• 😮‍💨 Coughing or nasal discharge
• 🍽️ Decreased appetite
• ⚖️ Progressive weight loss

This bacterium forms abscesses in the lungs, making it hard to detect early. Diagnostic imaging and a tracheal wash may be required. Treatment usually includes macrolide antibiotics + rifampin. 🩺

5. Nutritional Considerations & Mare Milk 🍶

Foals rely on their dam’s milk for the first few months, but not all mares produce enough. Risk factors for milk deficiency include:

• 🧓 Age or illness of the mare
• 💊 Use of certain medications
• ⚠️ Poor nutrition or stress

Watch for foals that:

• 🍼 Nurse constantly or become frustrated at the udder
• 🐴 Attempt to eat forage excessively early
• ⚖️ Appear thin or slow-growing

Provide a foal creep feed with 16–18% protein and balanced vitamins/minerals to support early transition. 🥣

6. Assessing Body Condition in Foals 🧠

Foals carry fat differently than adult horses. Key areas to assess include:

• 🟫 Withers and behind the elbows
• 🔲 Less so along the ribs and back

Note: Ribs may be visible in a healthy, lean foal. Don't rely solely on rib visibility—use a full-body evaluation and observe energy levels, coat condition, and behavior. 🧐

7. Other Causes of Weight Loss in Foals ⚠️

• 🔋 Nutrient malabsorption
• 🧬 Congenital disorders
• 🧪 Trace mineral or vitamin deficiencies
• 🧬 Genetic or metabolic diseases (rare)

If common causes have been ruled out, advanced diagnostics such as blood panels, fecal cultures, and imaging may be needed. 🧬🔬

8. Prevention Tips for Healthy Growth ✅

• 📆 Regular deworming starting at 2 months
• 🛡️ Vaccination per vet recommendations
• 🔬 Periodic fecal and blood testing
• 🍽️ High-quality mare and foal feed
• 💉 Early treatment of any illness or infection

Keep a growth chart to monitor weight, height, and condition monthly. Rapid changes or sudden slowdowns should prompt a vet exam. 📈

9. Summary Chart: Foal Weight Loss Causes & Clues 📋

10. Final Thoughts from Dr Duncan Houston 💬

Foals are incredibly resilient—but also vulnerable. Weight loss around three months of age is a red flag that should never be ignored. Whether the cause is parasites, infection, or nutrition, early intervention is key to restoring health and setting your foal on the right path. 🐴📈

If your foal isn’t thriving, schedule a veterinary checkup and consider testing for roundworms, respiratory infections, and intestinal disease. For customized feeding plans and health tracking tools, visit AskAVet.com or download the Ask A Vet app 📲 for expert guidance tailored to your young horse.

— Dr Duncan Houston, BVSc