My first horse in his 20s was once every other year.
My second was annual.
My third horse was annual until about six years ago when I started having twice yearly touch ups. The vet always says he can wait, but he’s happier with a minor touch up and doesn’t need sedation for the hand float.
Youngest horse is annual hand float in the fall, and the vet usually says he could wait until spring.
The significant information is this:
Horse #1 a handful of grain when I went out, effectively no grain before I bought him.
Horse #2 regular grain throughout his life 1-4lbs per day.
Horse #3 almost no grain up until about seven years ago, then pretty regularly 4-6lbs per day.
Horse #4 very little grain - and it’s soaked pellets.
Why is that more significant than age, breed, discipline, dental professional, float method? Because horses use a smaller grinding circle motion with the lower jaw when chewing grain than when chewing long stem forage. This means they don’t get the same degree of coverage tooth to tooth and wear unevenly which in turn affects the grinding circle. I learned that from a magazine ages ago - someone had put marker dots on the horses, filmed them eating and analyzed the motion.
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I have always had my vet hand float without sedation (except for maybe three occasions) and they have always used a speculum.