BMI is a number, it's calculated from height and weight (or mass if the physicists want to get fussy).
It is not, of course, dependent on race or even species. You can calculate it for a horse if you have nothing better to do. ( I suspect that a horse that was starving to death would end up with a BMI that indicated that it was grossly obese if you compared it to human "normal" values.)
What you do with that number is another matter. If you want to use it as some sort of proxy measure for health then you need to take a lot more things into account (like race, muscle mass, sex, age etc) or you can just accept that it isn't as good a measure as it might be.