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

Thankfully, a horse going into toxic shock following a vaccination is rare, but we've had our share of clients over the years whose horse hasn't had a great experience following a vax. For those of you who have been with us a few centuries you may remember the very gorgeous Zac who significantly crashed after a jab, and for a moment there it was serious touch and go. However, his lovely owner kept the faith, followed the detox programme, and Zac pulled through.

So what to do? You may have you’ve noticed your horse seeming a bit 'off' after a vax, maybe 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 your horse being '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 laminitis or metabolic flare-ups. Worse, a horse may go into toxic shock.

Why vaccination plans should be individualised

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, helping to regulate the immune response and counteract the inflammatory effects of omega-6s. Horses grazing on decent pasture for more than 8-hours a day generally get enough omega-3s, but during winter or dry spells, supplementation is a must. Micronised linseed fills this gap, providing the same omega-3 profile as fresh grass - perfect for year-round nutrition.A nutritional marvel, micronised linseed is a rich source of omega-3 fatty acids, soluble fibre, protein, and essential vitamins and minerals.

Top Tip - Horses on hay-only diets will have an omega-3 deficiency, as it's lost during the drying/curing process of grass to hay. Our VitaComplete balancer compensates for this loss.

On the flip side, many commercial feeds are loaded with omega-6s from soya or oils which can tip the scales toward inflammation.

• Think soya’s a superfood? Think again. Soya  is far from the nutritional silver bullet it’s claimed to be and poses serious risks to horses. Usually GM and heavily sprayed with chemicals, soya is nutritionally inappropriate for horses, causing digestive issues, hindgut acidosis, and blocking absorption of essential minerals like calcium and zinc. Its amino acid profile leads to water retention in muscles and not protein building, while its starch ferments in the hindgut, disrupting gut health. Soya’s inflammatory fats, anti-nutrients, and phytoestrogens contribute to allergies, infertility, and poor overall health.
  
  Soya's a nutritional No. More on our Soya page for the full picture.

• Fact - horses aren’t evolved to digest liquid oils, yet so many of us slosh a glug from a supermarket oil into the feedbowl, very often on the advice of our vet. Yet there's a very good reason why we shouldn't do this!
  
  The equine liver is designed to produce only a small trickle of bile - just enough to handle the minimal essential fatty acids (EFAs) found in forage. This matches a horse’s natural trickle-feeding process, whereas adding extra liquid oil to the diet overwhelms digestion, creating a physical blockage that disrupts digestive enzyme function. This prevents proper digestion of starch and protein, and throws off fibre fermentation in the hindgut. The result? A cascade of issues, including colic, laminitis, and leaky gut. And yes, this also includes linseed oil!
  
  Liquid oils do more harm than good, offering little real energy benefit while posing serious health risks. Discover more about why oils are a slippery slope for our horses in our Oils page.

2. Reduce sugar and starch

Refined sugars and starchy grains quickly break down into glucose, causing a rapid spike in insulin levels. Insulin, being an inflammatory fat-storage hormone, can trigger a cascade of negative effects throughout the body, especially when levels are consistently elevated. Over time, this will compromise your horse’s metabolic health, contributing to issues like insulin resistance, laminitis, and systemic inflammation. By minimising the sugar and starch content in your horse’s diet, you'll support a more stable metabolic state, promoting better overall health, improved gut function, and greater resilience against equine health challenges.

3. Avoid glyphosate contamination

Glyphosate, a widely used herbicide classified as a known carcinogen, is a hidden hazard lurking in many non-organic horse feeds. This chemical has been linked to significant health concerns, including gut biome disruption, immune system dysfunction, and long-term systemic issues. Ingredients like soya, beet pulp, and alfalfa are particularly prone to glyphosate contamination unless they are Certified Organic or guaranteed non-GMO - both of which are rare and hard to source.

Opting for clean, chemical-free feeds and supplements is one of the most impactful steps you can take to safeguard your horse’s health, ensuring they thrive without the burden of hidden toxins.

4. Plug the nutritional gaps

While grass and hay serve as the forage foundation of a horse’s diet, they don't provide all the essential nutrients needed to thrive - we know our UK grass is deficient in numerous minerals and amino acids, with hay also falling short in omega-3 EFAs and vitamin E. This means a well-rounded mineral balancer, such as our EquiVita (summer) or VitaComplete (winter or hay diets), is an essential to our horse's feeding routine.

To further support overall health, consider incorporating high-quality protein sources like hemp seeds, which not only help meet your horse’s protein requirements but also offer natural anti-inflammatory properties, promoting muscle development, recovery, and resilience. Together, these additions create a more balanced and nourishing diet for your horse.

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

If you're on a livery yard or competing, 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.