Guest contribution by Juliet M. Getty, Ph.D.

If you’ve noticed your horse feeling a bit “off” after their vaccinations, you’re not alone. Perhaps they’ve seemed more subdued, sensitive to touch, or just not their usual selves. It’s a reaction that can make even the most experienced horse owner uneasy. But what’s really going on?

It all comes down to inflammation - a natural response triggered by vaccines as the immune system gears up to protect your horse. While inflammation serves an important purpose, it can also create short-term discomfort or, in some cases, stress the body, especially if the immune system is already compromised.

Dr. Juliet Getty, a revered equine nutritionist who’s taught me much over the years, recently shared some insights into the science behind vaccine-induced inflammation. Here’s what we know and, more importantly, what we can do to support our horses through it.

What the research tells us

A study conducted by Kansas State University’s College of Veterinary Medicine explored how routine vaccinations affect inflammation in horses. The researchers monitored a biomarker called Serum Amyloid A (SAA), a protein that rapidly increases in response to infection, stress, or injury. Think of SAA as your horse’s internal alert system - when levels rise, it signals that the immune system is reacting to something.

Here’s what they found:

• SAA levels spiked after vaccination, with most horses (85.7%) returning to normal levels within 10 days.
• Fevers were common, with 78.6% of vaccinated horses showing body temperatures above 38.4°c.

These findings confirm that vaccines temporarily increase inflammation. For most horses, this response resolves within a week or so. However, horses with underlying health issues, such as PPID (Cushing’s), metabolic syndrome, or those under chronic stress - may experience longer recovery periods.

Understanding inflammation in horses

Inflammation is the body’s way of defending itself, whether it’s from infection, injury, or, in this case, a vaccine. The immune system recognises the vaccine as a foreign invader and launches a controlled response to fight it. This is how immunity develops, but it’s also why you might notice symptoms such as:

• Lethargy or depression
• Loss of appetite
• Increased sensitivity to touch
• A general sense of “not quite right”

While these symptoms can be unsettling, they’re usually short-lived. However, chronic or excessive inflammation is where the real risks lie. Left unchecked, it can weaken the immune system, disrupt gut health, and even contribute to conditions like laminitis or metabolic flare-ups.

Why vaccination plans should be individualized

Not all horses need the same vaccines - or the same schedule. Older horses, for example, may experience immunosenescence, a gradual weakening of the immune system that makes them more vulnerable to stressors like vaccines. Spacing out vaccinations for these horses can help prevent overwhelming their systems.

Similarly, if your horse is already dealing with health challenges like PPID, metabolic syndrome, or a history of laminitis, it’s worth discussing their vaccination needs with your vet. The goal is to balance protection against disease with minimising unnecessary strain on the body.

The role of diet in managing inflammation

Here’s where we as horse owners can make a huge difference. Nutrition plays a central role in supporting the immune system and keeping inflammation in check - before and after vaccinations.

1. Balance omega fatty acids

Omega-3s are nature’s anti-inflammatory superheroes. Found in chia seeds and flaxseed, omega-3s help regulate the immune response and counteract the inflammatory effects of omega-6s. Horses grazing on lush pasture for more than 8 hours a day generally get enough omega-3s, but during winter or dry spells, supplementation is a must.

On the flip side, many commercial feeds are loaded with omega-6s from soya, corn, or sunflower seed oils which can tip the scales toward inflammation. Avoid these oils where possible, and opt for balanced, natural fat sources.

2. Reduce sugar and starch

Refined sugars and starchy grains break down into glucose, spiking insulin levels, insulin being an inflammatory hormone. The lower the sugar and starch content in your horse’s diet, the better their overall health and resilience.

3. Avoid glyphosate contamination

Glyphosate, a known carcinogenic herbicide found in many non-organic feeds, has been linked to gut health issues and immune dysfunction. Soya, beet pulp, and alfalfa are common culprits unless certified organic or non-GMO, which is rare. Choosing clean, chemical-free feeds and supplements is one of the simplest ways to support your horse’s health.

4. Fill nutritional gaps

While hay is a diet staple, it’s not a complete source of all essential nutrients. Pair it with a well-rounded mineral balancer (like EquiVita) and consider high-quality protein sources like hemp seeds, which also offer anti-inflammatory benefits.

Stress: the inflammation trigger

Stress is a sneaky contributor to chronic inflammation, making your horse more vulnerable to infections, allergies, and exaggerated inflammatory responses.

Where possible, let your horse live as naturally as they can. Allowing for movement, social interaction, and consistent access to forage can make a world of difference. Even small changes - like placing hay in multiple locations to encourage movement - help reduce stress and support overall health.

The bottom line

Vaccines are considered a necessary part of equine care, but they’re not without their challenges. Understanding the inflammatory response and taking proactive steps to support your horse’s recovery can make the process smoother for everyone involved.

Every horse is different, so work with your vet to tailor a vaccination plan that suits your horse’s age, lifestyle, and health. And remember, a balanced diet and a stress-free routine are your horse’s best allies in maintaining a strong immune system - not just after vaccines, but all year round.

A word of thanks

A huge thank you to Dr. Juliet Getty for sharing her expertise. Dr. Getty’s work has inspired countless horse owners (myself included – you’ll see her quoted many times throughout our website) to approach equine care with curiosity and confidence. For more of her insights, visit her Equine Nutrition Resource Library.