Hi team… how’s your grass looking?
I’m guessing many of you who have had all the rain over the last week have watched your paddocks go from brown to bright green almost overnight!
If that’s happening in your horse’s paddock, have you also noticed your normally sensible horse suddenly becoming a bit… extra? 
So what’s actually happening inside your horse?
After weeks of heat and dry conditions, the grass has gone from being stressed to absolutely loving the warm, wet weather. It responds by growing rapidly and ramping up photosynthesis, producing and storing more sugars.
And guess who gets to eat all that lush, sugary grass?
Yep… your usually sensible little unicorn! 
What happens next?
That sugar-rich pasture enters your horse’s foregut, where it moves through much more quickly than the older, mature, high-fibre pasture your horse was eating just a week ago.
As a result, more rapidly fermentable carbohydrates reach the hindgut sooner than usual.
The microbes living in the hindgut are adapted to a relatively stable, fibre-based diet. When a sudden flush of sugars arrives, the balance of those microbes changes rapidly. This can lower hindgut pH and disrupt the normal microbial population—a condition known as hindgut dysbiosis.
Here’s an easy way to picture it…
Imagine the hindgut is a sports field.
Most of the time, the Blue Team is playing. They’re the fibre-fermenting microbes—steady, reliable and happy working on hay and mature pasture.
Then suddenly, a huge load of sugar arrives = aka Red Team.
The Blue Team can’t keep up, as the aggressive Red Team rushes onto the field. They love sugars and multiply quickly. They take over from the Blue Team and push them off the field! Before long, the whole game has turned into complete chaos!
Okay… maybe I’ve pushed the analogy a little far… 
But hopefully you get the idea.
A sudden increase in lush pasture can upset the delicate microbial balance in the hindgut, and because the gut communicates with the brain through the gut-brain axis, these changes may influence behaviour as well as digestive health.
So if you’re wondering, “Where did my lovely, sensible pony disappear to?”… this could be part of the answer.
What can you do?
Increase fibre intake with low sugar hay, chaff and soyhulls or beet pulp. Avoid letting horses gorge on lush pasture. Strip graze or limit access to rapidly growing pasture where appropriate. Use fats rather than grain if additional calories are needed. Consider adding a quality prebiotic to support hindgut microbes. Ensure the diet is balanced for vitamins and minerals, as nutritional deficiencies can compound these issues.
Remember, not every horse will react the same way. Horses prone to laminitis, Equine Metabolic Syndrome (EMS), PPID (Cushing’s disease), or those that are naturally “good doers” are often the most sensitive to these rapid pasture changes.
If you’re unsure whether your horse’s diet is appropriate for the current pasture conditions, now is a great time to have it assessed by an independent equine nutritionist.
For more information see:
Feed Terminology – Fructans, Fibre, Sugar, NSC – What do they all mean???
Dale Logan
BSc, Post Grad Dip, Equine Nutrition, Massey University.
Equine Nutrition Advanced Uni of Guelph, Cert Equine Herbal Medicine, Cert NZ Animal Welfare Legislation
