I've worked with senior horses for a long time, and weight loss in older horses was one of the most frustrating things I dealt with early on. I kept throwing more feed at the problem and wondering why nothing stuck.
Eventually I stopped guessing and started actually diagnosing. Here's what I learned:
First, rule out the obvious culprits
Dental issues are the #1 thing people miss. An older horse can't properly chew hay or grain if their teeth are worn or sharp. Get a vet to do a float before changing anything else — it made a massive difference for one of my mares who I'd been struggling with for months.
Forage first, always
Grain won't fix a horse that isn't getting enough quality forage. For seniors who struggle with long-stem hay, soaked beet pulp and hay cubes or pellets are game-changers. They're easier to chew and digest.
Fat over sugar
Adding fat (rice bran, stabilized flaxseed, or a senior-formulated feed with higher fat content) is a much cleaner way to add calories than piling on grain. Less digestive stress, steadier weight gain.
Hindgut health matters more than people think
Older horses are more prone to hindgut issues that tank nutrient absorption. A good probiotic and limiting starch helped two of my horses more than any feed change.
Parasite load
Fecal egg counts are worth doing regularly — even horses on routine deworming schedules can carry surprising loads.
Happy to answer questions if anyone's dealing with a hard keeper senior.