Most important ingredients in a horse's joint supplements?

Your horse's diet probably provides the ingredients in the second supplement. There is no documented deficiency of biotin in equines, so it is a choice to feed it based on the belief that it may help something like the hooves. But nobody feeds it because a deficiency has been identified through testing, since horses are just not measurably deficient in biotin. If your horse is being reasonably well fed, then the fatty acids she needs are probably already in her diet.

I wouldn't spend one dime on anything other than what you are looking for in a joint supplement. I'd choose the Matrix. But, I will just mention that some of what is in it should not be fed to your horse if there is any question that she is insulin resistant, since glucosamine should not be fed if that is the case. If your girl is for certain not insulin resistant, the Matrix sounds like what I would choose. But my vet would be determining this with me.

Use Adequan injections if you really want to improve your horse's joint function. It is FDA approved and actually works because it is a fluid injection.