I still cringe thinking about my first high-altitude pack trip in Colorado's San Juan Mountains. I'd spent 3 months training my 12-year-old Quarter Horse mare Lila on low-elevation (5,000-foot) trails, perfecting her packing skills and building up to 15-mile days, and was convinced we were ready for our 5-day trip to 10,200 feet. She was perfect on day one. By day three, she was dragging on climbs, refused to eat her hay, and had a respiratory rate 10 beats higher than her normal resting rate. We turned back two days early, and I spent $800 on a vet house call to confirm she was severely dehydrated and had mild digestive upset from the altitude and low-quality alpine forage. That humbling (and expensive) wake-up call taught me a hard lesson: high-altitude trail riding isn't just "regular trail riding with thinner air." The combination of reduced oxygen, dry climate, unpredictable high-elevation forage, and increased energy demands requires specialized nutrition planning that no standard low-elevation trail prep can cover. Over the next two years, I tested dozens of adjustments with Lila and our large animal vet, and we've now completed 8 successful high-altitude expeditions, including a 7-day ride to 13,000 feet in the Wind River Range. These are the rules that kept her strong, well-fed, and eager to keep climbing when the air got thin.
Pre-acclimate her metabolism 2--3 weeks before you even leave for the trail
Most riders focus exclusively on physical conditioning for high-altitude trips, but your horse's metabolic system needs time to adjust to lower oxygen levels long before you hit the trail. At elevation, her body burns energy 20--30% faster to compensate for reduced oxygen in the blood, and she processes simple carbs far less efficiently than at low elevation, making her prone to energy crashes and muscle fatigue. Start 3 weeks out: shift 2 of her weekly training sessions to a higher elevation site (8,000--9,000 feet if you live at sea level, or 1,000--2,000 feet higher than your home elevation if you already live in the mountains) so her body adjusts gradually. Swap 10% of her regular grain ration for a high-fat, low-sugar supplement like rice bran or stabilized flaxseed 2 weeks pre-trip: fat delivers 2.25x more energy per pound than carbs, and requires less oxygen to metabolize, making it the most efficient fuel source for altitude. For our Wind River trip, we cut Lila's sweet feed (high in corn and molasses) by a quarter and added a cup of rice bran to her morning and evening meals, and she had steady, consistent energy the entire 7 days, no mid-trip crashes.
Prioritize consistent, high-quality forage over grazing alone
Alpine and desert high-altitude forage is notoriously unpredictable: it can be coarse, low in digestible fiber, or even toxic depending on the region and time of year, and many horses lose their appetite for rough, wild grasses once they're at elevation. Relying solely on grazing is a fast track to weight loss, impaction colic, or sudden energy crashes. Pack 1.5x the amount of hay you'd normally feed for a low-elevation trip of the same length, and store it in waterproof, airtight bags to keep it from getting damp or moldy in your pack. Offer small, frequent forage meals (every 2--3 hours on long climb days) instead of 2 large meals a day, to keep her gut moving and encourage consistent eating even if she's not hungry for larger portions. If you do let her graze, scout the area first for toxic plants (locoweed, larkspur, and tall larkspur grow in abundance at high altitude) and limit grazing to 30 minutes at a time for the first 2 days to let her digestive system adjust to the new forage. Pro hack: Soak dry hay in warm water for 10 minutes before feeding if she's reluctant to eat coarse mountain hay---this makes it easier to chew and more palatable, and adds extra hydration to boot.
Adjust your hydration and electrolyte routine for dry, thin air
You might not see your horse sweating as much at altitude as you would at low elevation, but she's losing far more water through respiration thanks to the dry, thin air---up to 30% more than she would on a similar ride at sea level. Dehydration hits twice as fast at altitude, and even mild dehydration will kill her appetite, slow her gut, and increase her risk of colic. Offer water every hour on the trail, even if she doesn't seem thirsty, and keep a thermos of warm water handy if she refuses to drink ice-cold mountain stream water (a super common issue, since cold water can slow digestion and make horses reluctant to drink enough). Skip generic "sweat" electrolytes that are loaded with sugar, and opt for a low-sugar, high-sodium/potassium formula designed for endurance riding---add it to her water and feed every 4 hours on long days. Avoid over-supplementing magnesium, which can cause diarrhea and digestive upset at altitude, where gut motility is already slower than normal. Quick dehydration check: Pinch the skin on the side of her neck (it's thinner and more reliable than the shoulder skin at altitude) and hold for 2 seconds---if it takes more than 3 seconds to snap back, she's dehydrated, and you need to stop for a 15-minute water break immediately.
Stick to slow-burning, low-sugar energy sources
It's tempting to load up on sweet feeds or high-carb treats to give your horse a quick energy boost for tough climbs, but simple sugars cause rapid spikes and crashes in blood sugar, and increase lactic acid buildup in muscles at altitude, leading to tying up, fatigue, and poor performance. Stick to high-fiber, high-fat feeds as her primary energy source: beet pulp, alfalfa pellets (if she tolerates them), or specialized high-fat trail pellets are all better options than sweet feeds or corn-based grains. If you do give treats, stick to low-sugar options like plain carrots, celery, or unflavored horse cookies, and limit treats to no more than 1 cup a day to avoid disrupting her gut bacteria. For summit push days, add an extra ½ cup of rice bran to her midday meal 2 days before the climb, not the day of, to give her body time to adjust to the extra fat and avoid digestive upset.
Proactively protect her gut to avoid colic
Colic risk is 3x higher on high-altitude trail trips, thanks to dehydration, lower forage quality, changes in routine, and cold water intake. A colic episode at 12,000 feet, where the nearest vet might be 2 hours away, can be fatal, so prevention is non-negotiable. Start an equine probiotic supplement 2 weeks before your trip, to build up healthy gut bacteria that will help her digest new forage and adjust to routine changes. If she's prone to impaction colic, add 1--2 tablespoons of psyllium husk to her daily feed for the 2 weeks leading up to the trip, to keep her gut moving smoothly even if she's drinking less water than normal. Never switch her feed abruptly on the trail---bring the exact same hay and grain she eats at home, and introduce any new supplements at home first to make sure she tolerates them. If you have to switch to local hay mid-trip, mix it with her regular hay for 3 days before switching fully, to let her gut adjust.
Adjust rations based on your trip phase, not just daily mileage
Your horse's energy and nutritional needs change drastically depending on whether you're ascending, summiting, or descending, so don't stick to the same feeding schedule the entire trip.
- Pre-ascent (first 2 days at elevation): Keep portions 10% smaller than you would at low elevation, and offer water and forage every hour. Her body is adjusting to the thin air, and overfeeding will increase her risk of digestive upset and altitude sickness.
- Summit/climb days: Increase her fat-based supplement (rice bran, flaxseed) by 10--15% for the 2 days leading up to the climb, not the day of. Offer small, frequent forage meals and electrolytes every 4 hours, and avoid long breaks where she's standing still in the cold, which can slow her gut and make her lose her appetite.
- Descent days: Taper the extra fat portions back to her normal home ration gradually over 2 days, as her oxygen levels return to normal and she doesn't need the extra energy-dense fuel. This prevents weight gain and digestive upset from too much rich feed once you're back at lower elevation.
What to Do If She Refuses to Eat Mid-Trip
Even with the best planning, some horses lose their appetite at altitude, especially on the first 2--3 days. Don't panic, and don't force her to eat: stress will only make the issue worse. Try these tricks first:
- Soak her hay in warm water with a splash of apple cider vinegar to make it more palatable.
- Add a small handful of her favorite treat (carrots, apple slices, unflavored horse cookies) to her feed ration.
- Offer warm water instead of cold, and add a splash of apple juice to the water if she's really reluctant to drink. If she goes more than 12 hours without eating any forage, or shows signs of severe lethargy, colic, or respiratory distress, descend to the lowest elevation possible immediately and call a vet.
After that first failed trip to the San Juans, I learned the hard way that high-altitude trail riding isn't just a test of your horse's fitness---it's a test of how well you can adjust her care to the unique conditions of thin, dry air and unpredictable forage. It takes a little extra planning and a few extra pounds of hay in your pack, but it's worth it to avoid cutting your trip short, or worse, dealing with a life-threatening colic or exhaustion episode miles from help. Last summer, Lila carried a 30lb pack and me 18 miles round-trip to a 13,000-foot alpine lake, ate every bite of her hay, and even nickered at me when I pulled out her post-ride rice bran treat. Trust me, that's way better than turning back early and explaining to your trail partners why you have to bail on the summit push.