Not only do I (and other people at my barn so I don't think I'm just barn blind LOL) notice a difference in my 13 year old ex-racer but I know a gentleman who started using it on his aged mastiff and he said he noticed a difference after just two injections. I personally feel it's very effective as well as affordable. Good, good stuff.
'10 Dolce Latte G - Thoroughbred Mare (chestnut at that!)
'12 Genever - KWPN/Thoroughbred Mare
There are lots of people using Pentosen that frequent the board...There is actually a thread on this forum right now if you scroll down a bit...or some others from before if you search for them...Lots of people seem to be happy with it...Good luck with your horse.