What Your Horse's Feed Is Actually Doing Inside Them
KEY TAKEAWAYS
- Every feeding chart is built for an average horse that doesn't exist. Workload, temperament, age, and environment all change the equation.
- Fiber, fat, and starch behave completely differently in the body. The fuel type matters as much as the calorie count.
- Your horse's gut was designed for 16 to 18 hours of continuous grazing. Most modern feeding schedules work against that design.
- Fat provides 2.25 times more energy per pound than starch and doesn't spike blood sugar. Research shows it reduces reactivity and excitability.
- True fat adaptation takes 4 to 6 weeks. What you see in week one tells you very little about what week six will look like.
Your horse had a good session last week. Today she's stiff, a little resistant, and not quite herself. You haven't changed anything. Same hay, same grain, same schedule.
Or maybe it goes the other direction: she's electric in warm-up, sharp in a way that doesn't settle, and by the third canter transition something has switched and now she's flat and checked out.
Both of those are feed stories. They just don't look like it.
The gap between what goes in the bucket and what actually happens in the body is where most feeding frustrations live. This guide covers what happens after the lid goes back on. How the gut was designed to work. Why the type of fuel you're feeding matters as much as the amount. And why fat, specifically, changes both stamina and behavior in ways most horse owners don't expect.
Everything here comes from four sessions of ScoopRx Office Hours. No outside research. Just the science behind what Shana covers every week.
WHY EVERY FEEDING CHART IS BUILT FOR A HORSE THAT DOESN'T EXIST
Every recommendation you find starts in the same place: the National Research Council (NRC) maintenance requirements. For a 1,100-pound adult horse in a temperate controlled climate doing no work, that baseline is roughly 16 Mcal of digestible energy per day, with forage at 1.5 to 2.5 percent of body weight daily.
That horse does not exist at your barn.
Real horses work, age, live through seasons, and carry different metabolic tendencies. The NRC values are minimums. Many equine nutritionists recommend going 25 to 50 percent above those values for vitamins and minerals alone. And that's before any of the individual factors that actually describe your horse.
Workload is the first variable most people get wrong
Light work, which means trail riding, early training, and basic arena work, requires about 20 percent more energy than maintenance. Moderate work, including school horses and working ranch horses, requires 40 percent more. Heavy work, eventing and race training, adds 60 percent. Elite competition horses may need as much as 80 percent above baseline.
Most pleasure horses fall into the light work category. Most of them are being fed for moderate. The gap shows up as a horse that's a little heavier than ideal, a little less sharp than expected, or reactive in ways that don't track with their training.
Temperament tells you which fuel to reach for
Easy keepers and hard keepers don't just need different amounts. They need different types of fuel. Easy keepers do best with low-NSC hay (under 12 percent combined sugar and starch), a ration balancer instead of a full concentrate, and slow feeders to extend forage time without adding calories.
Hard keepers often need added fat as a source of what's called cool calories. Hot and cool aren't about temperature. They describe how different fuel sources affect the horse's energy and behavior. Starch and sugar release fast. Blood sugar spikes. The horse is suddenly wired. Fat and fiber release slowly and steadily. The horse stays consistent.
Age changes the whole picture
Growing horses up to age three need 14 to 16 percent crude protein and a calcium-to-phosphorus ratio of 1.5 to 2 to 1. Excess energy in young horses increases the risk of developmental orthopedic disease. Mature horses do well on 8 to 10 percent crude protein matched to actual workload. Senior horses, generally 18 and older, often need 12 to 14 percent crude protein in easily digestible forms, and may need soaked feeds when dental changes become a factor.
Environment is the layer most feeding programs ignore
Cold weather increases energy needs by roughly 2.5 percent for each degree below the horse's lower critical temperature, around 5 degrees Fahrenheit. More forage, not more grain, is the right response. Fiber fermentation in the hindgut generates internal body heat. Hot weather drives electrolyte losses through sweat: sodium, potassium, and chloride all need to be replenished. Spring pasture can carry nearly double the sugar of late summer grass, which matters significantly for easy keepers and metabolically sensitive horses.
Body condition scoring gives you an objective baseline
The Henneke Body Condition Score (BCS) scale runs from 1 to 9. The ideal range for most horses is 4 to 6. You score in six areas: neck, behind the shoulder, withers, ribs, loin, and tailhead. Always palpate. A thick winter coat or a naturally round breed will fool your eyes. Track the trend over multiple months rather than reacting to a single moment.
THE SAME CALORIE IS NOT THE SAME FUEL
Two horses can eat the same amount and perform completely differently. One holds weight, stays consistent under saddle, and recovers well between rides. The other gains and loses weight in cycles, spooks at things that didn't used to bother her, and runs out of engine by the middle of every session.
The difference is usually not how much they're eating. It's what kind of fuel they're running on.
Fiber: the base fuel
Roughly 70 percent of a horse's usable energy comes from fiber fermentation in the hindgut. Microorganisms in the cecum and colon break fiber into volatile fatty acids, specifically acetate, propionate, and butyrate, which are absorbed and converted to energy. This is a slow, steady process. A horse running on fiber has a consistent energy supply and a calm, even baseline.
Fat: the most energy-dense option available
Gram for gram, fat provides 2.25 times more energy than starch or carbohydrates, with an 88 to 98 percent digestibility rate. It doesn't trigger insulin release. It doesn't spike blood sugar. The energy it delivers is sustained and even, and the horse burns it through a completely different metabolic pathway than starch.
A horse who runs on fat for aerobic work looks different under saddle. Steadier. More consistent. In possession of their energy instead of fighting it.
Starch: the quick burst with a real cost
Starch from grain breaks down to glucose in the small intestine, triggering a rapid insulin response and a blood sugar spike. The horse is suddenly very forward, very alert. Then the spike passes. That's the horse who feels electric in warm-up and flat by the third canter.
What makes starch genuinely problematic at high volumes isn't the spike itself. It's what happens when the small intestine gets overwhelmed and excess starch spills into the hindgut. The hindgut wasn't designed for starch. When starch arrives there, it disrupts the microbial population, acidifies the environment, and can set off a cascade that includes colic and laminitis. Keeping grain meals under 5 pounds (2.25 kilograms) per feeding keeps starch in the small intestine where it belongs. For horses who need lower sugar, soaking hay for 30 to 60 minutes reduces its sugar content by up to 50 percent.
YOUR HORSE'S GUT WAS BUILT FOR A LIFE YOUR HORSE DOESN'T LIVE
The horse's digestive system evolved for one thing: continuous grazing. Sixteen to eighteen hours a day. Small bites of forage, steady and constant, across open land.
What we've built instead is two meals a day, significant grain, and several hours of nothing in between. The anatomy hasn't changed. The schedule has.
The stomach is smaller than you think, and it never stops making acid
The horse's stomach makes up only 10 percent of the total gastrointestinal tract. It wasn't built to hold large volumes at once. What it does do, without stopping, is produce acid. Twenty-four hours a day, whether the horse has eaten or not.
Natural grazing generates up to 40,000 chews per day and roughly 36 liters of alkaline saliva, which buffers that acid constantly. A horse eating two meals a day with long gaps in between has the continuous acid production without the continuous buffer.
One part of the stomach has no protection
The lower glandular region produces acid and has a mucus lining to protect itself. The upper squamous region has nothing. When the stomach is empty or when the horse moves at speed, acid splashes onto that unprotected surface. This is where approximately 80 percent of gastric ulcers form.
Forage changes this. A horse with hay in their stomach has a physical fiber mat that blocks acid from reaching the squamous region. Feeding as little as 300 grams of hay before exercise has been shown to protect against squamous ulcers. A horse exercising on an empty stomach has nothing blocking that acid splash.
Ninety percent of racehorses develop gastric ulcers during active training. Roughly 60 percent of pleasure horses experience them at some point. The signs usually don't look like stomach pain. They look like poor performance, girthiness, reluctance to work, and behavioral changes that don't have an obvious explanation.
The hindgut needs consistency more than anything
The cecum and colon convert fiber into volatile fatty acids that provide 60 to 70 percent of the horse's total energy. The microorganisms doing that work are diet-dependent. An abrupt feed change can shift the microbial population within 24 hours, disrupting fermentation, dropping the pH, and triggering inflammation that shows up as diarrhea, colic, or worse.
Colic is the leading cause of premature death in horses. A significant number of those cases trace back to digestive management decisions: abrupt feed changes, long fasting gaps, large grain meals. Transitions between feeds should always happen over 10 to 14 days. Slow feeders double the time a horse spends eating, reduce hay waste by about 50 percent, and better match how the gut was actually designed to work.
The rules that follow from the anatomy
- Feed hay before grain, every time. The fiber mat forms first.
- No fasting gaps longer than four hours. Acid is working the entire time.
- Grain meals under 5 pounds (2.25 kg). Larger amounts overflow the small intestine.
- At least 300 grams of hay before any exercise. It protects the squamous region from acid splash.
- Ten to fourteen days minimum for any feed change. The microbiome shifts within 24 hours of a change.
WHY FAT MAKES HORSES CALMER, NOT HOTTER
This is the part that surprises most people.
Adding fat to a horse's diet does not make them more energetic, more reactive, or harder to handle. It does the opposite. Research from Virginia Tech found that horses on high-fat diets showed measurably reduced reactivity to startling stimuli, lower excitability scores, and lower anxiety scores compared to horses on grain-based diets. The mechanism isn't sedation. It's the removal of the blood sugar roller coaster that starch creates.
No spike means no surge of cortisol and adrenaline. No glucose crash means no flatness or sourness on the back end of a ride. The horse who used to feel like a powder keg in warm-up starts to settle. The one who ran out of engine has a fourth and fifth canter.
The performance case is just as clear
Forage contains only 2 to 4 percent fat. When you add fat beyond that baseline, the horse's body shifts toward using it as the primary fuel for aerobic work. Most of what horses do in training is aerobic. When fat fuels that work, muscle glycogen is preserved rather than burned early. Glycogen is what muscles reach for during hard efforts. A fat-adapted horse goes into the final fence, the last miles of a trail, or the demanding end of a lesson with more glycogen still in reserve.
Fat also produces less heat during digestion than either starch or fiber. Fat-fed horses lose approximately 12 percent less water during exercise, which reduces thermal stress and supports hydration through longer efforts.
The sweet spot is 5 to 10 percent of the total ration as fat. Going above 10 to 12 percent adds calories without adding any additional performance benefit.
Not all fat sources are the same
The omega-3 to omega-6 ratio is what separates them. Grain-heavy diets already skew heavily toward omega-6, which is pro-inflammatory. Fat sources that shift the balance toward omega-3 offer anti-inflammatory support on top of the caloric benefit.
| Fat Source | Omega-3:6 Ratio | Best For |
|
Corn oil |
2:28 | Palatability, coat shine (heavily omega-6) |
| Soybean oil | 1:6 | Widely available, moderate omega balance |
| Canola oil | 1:2 | Best calorie-to-omega trade-off of common oils |
| Flaxseed or flax oil | 4:1 | Anti-inflammatory support for joints, skin, and airways (ALA) |
| Stabilized rice bran | 1:20 | Weight gain; 20% fat plus fiber, easy to top-dress |
| Fish oil | 6:1 | Pre-formed EPA and DHA; potent anti-inflammatory in small doses |
One important pairing: added dietary fat can interfere with vitamin E absorption. The guidance is to add approximately 1 to 2 IU of vitamin E per milliliter of oil in the diet.
How to introduce fat without disrupting the gut
Start small. Roughly one-quarter cup of oil, one-quarter pound of rice bran, or one-half pound of an extruded high-fat feed per day. Double that amount weekly over 7 to 10 days to let the gut adapt. True fat adaptation, the metabolic shift where the horse reliably draws on fat for aerobic work, takes 4 to 6 weeks of consistent feeding. What you see in week one is not what you'll see in week six.
One note on easy keepers: fat is calorie-dense. Ponies, miniatures, donkeys, and mules gain weight quickly on high-fat diets. This approach is best suited to horses in regular work who need additional calories or behavioral support.
FAQ's
How do I know if my horse's current diet is working?
Body condition scoring is the most reliable objective tool. Use the Henneke Scale, score all six areas, and palpate rather than relying on visual assessment. A thick coat or a naturally round breed can hide more than you'd expect. Track the trend over multiple months, not a single weigh-in. A horse consistently sitting at BCS 4 to 6 with steady energy, a good coat, and consistent behavior is a horse whose diet is working.
How much forage does my horse actually need?
A minimum of 1.5 percent of body weight daily on a dry matter basis. Many horses in moderate work or with higher energy needs do better at 2 to 2.5 percent. Forage should never drop below 1 percent of body weight for any horse, regardless of weight management concerns. The digestive consequences of insufficient forage, including ulcers, hindgut acidosis, and colic risk, outweigh the caloric math.
What causes a horse to be hot or reactive under saddle?
Diet is one of the most underexamined contributors. High-starch meals create rapid blood sugar spikes that trigger cortisol and adrenaline responses. The horse who feels electric and hard to rate in warm-up is often responding to a metabolic surge, not a training problem. Replacing starchy calories with fat and fiber sources removes that blood sugar rollercoaster. The Virginia Tech research on high-fat diets showed significantly lower reactivity and excitability scores compared to grain-based controls.
What is the difference between gastric ulcers and hindgut issues?
Gastric ulcers form in the stomach, most commonly in the unprotected squamous region where acid splashes during exercise or extended fasting. They're addressed through feeding management (forage first, no fasting gaps longer than four hours) and sometimes medication. Hindgut issues, including acidosis, dysbiosis, and microbial imbalance, occur in the cecum and colon when starch overflows from the small intestine or when abrupt feed changes disrupt the microbial population. The two can co-occur. Both respond to better forage management, smaller grain meals, and gradual feed transitions.
How long does it take to see results from a dietary change?
It depends on what you're changing. Behavioral improvements from replacing starchy calories with fat often become visible within 2 to 4 weeks. Full fat adaptation, the metabolic shift toward fat as the primary aerobic fuel, takes 4 to 6 weeks of consistent feeding. Hindgut microbiome stabilization requires the same 10 to 14 day transition window. Body condition changes take weeks to months depending on how significant the adjustment is.
WHAT COMES NEXT
Feeding decisions compound. The horse you have in six months is shaped by what you do in the next six weeks: the hay you're offering, the fuel type in the bucket, how long you're letting gaps go between meals.
Most horses improve with a few targeted adjustments, not a complete overhaul. More forage, smaller grain meals, better fuel sources, and a consistent transition window for any change. The science is consistent once you understand how the gut works.
If you want to work through your specific horse's situation with Shana directly, Office Hours is where that happens. She covers the science live every week and takes questions in real time about your specific horse.