By: Dr Rosie Alcorn BVSc PG Cert VPS Cert AVP MRCVS
With the arrival of Storm Amy over the weekend, it feels like we’ve leapt straight from summer into autumn, and perhaps even edged into winter.
As the seasons change, so do our routines. Horses begin spending more time stabled, fields grow sparse, rugs come out of storage, and feeding plans change.
You’ve probably heard that dietary changes should be made gradually in horses, but have you ever stopped to ask why? What’s really happening inside your horse’s digestive system when you swap their feed or hay?
The answer lies deep within the horse’s gastrointestinal tract, in a hidden world known as the microbiome.
The equine microbiome refers to the vast community of bacteria, protozoa, fungi and viruses that inhabit your horse’s gastrointestinal (GI) tract.
These microbes play a crucial role in digestion, fermentation, nutrient absorption, immune function, and overall health.
In horses, the most important microbial activity occurs in the hindgut - specifically the cecum and large colon - where microbes assist in fermentation.
This is particularly significant for horses because they are hindgut fermenters, meaning they rely on microbial fermentation to extract energy from the fibrous forages that make up most of their diet.
The microbes in the hindgut ferment dietary fibre and convert it into volatile fatty acids (VFAs) - primarily:
Acetate
Propionate
Butyrate
These VFAs are then absorbed through the gut wall and into the bloodstream, where they serve as the horse’s primary energy source.
Different microbes specialise in digesting different components of the diet. Some thrive on fibre, others on starch or sugar.
When you suddenly change what your horse eats, the microbial population can’t keep up. This disrupts fermentation, leading to reduced energy production, poor nutrient absorption, and potentially serious conditions such as colic.
The microbiome is highly sensitive. It has evolved to remain stable under a consistent diet.
When the feed changes, whether it’s a new bag of hard feed, a switch from grass to hay, or even moving from one hay type to another, the microbial population must adapt to the new nutrient profile.
This adjustment doesn’t happen overnight.
It takes around 10–14 days for the microbiome to fully adjust to a new diet.
If the change happens too quickly, the “old” microbes begin to die off before the “new” ones have had time to multiply, leading to an imbalance called dysbiosis.
This imbalance can cause:
Diarrhoea
Reduced appetite
Weight loss
Colic
Inflammation of the GI tract
A weakened immune response
Think of it this way: in summer, if there’s a surprise cold and rainy day, you’re often caught off guard - no jacket, no umbrella - and you spend the day cold and uncomfortable.
However, in autumn, as the weather gradually changes, you’re prepared. You’ve swapped out your wardrobe, packed a raincoat, and have an umbrella ready. The change doesn’t catch you by surprise.
Changing a horse’s diet works the same way. A gradual transition gives the microbiome time to prepare, slowly phasing in the new feed while reducing the old, allowing the microbial community to adapt without shock or disruption.
Keyflow's Sensi-Care is a pre-digested palatable soothing muesli that is also cereal free making it gentle on the horses digestive tract and hind gut. Sensi-Care is a suitable product for a lot of horses at this time of year as it is high in oil and quality proteins which makes it perfect for building condition, muscle and topline when the grass quality drops and horses need an extra boost to keep them looking and feeling their best.
This gradual approach works not just for hard feed, but also when:
Switching forage types
Moving from pasture to stabled forage
Introducing new supplements
Changing feed brands
Our horses rely on us to manage their diet with care, especially as the seasons shift.
By understanding the delicate balance of the microbiome, we can make smarter choices that protect their health from the inside out.
So, as autumn arrives in full force, and with winter close behind, let’s make sure we’re not just digging out our raincoats, but also preparing our horses’ digestive systems for the months ahead: slowly, mindfully, and with science on our side.
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