I initially bought this for my older pet, but he sadly passed and since I had leftover, I started to give it to my 3 year old hound/pit mix. I was shocked to discover that suddenly he wanted to run hard for an extended period of time. I thought it was a fluke, so when it ran out, I didn't buy more. Within a couple of months, he went back to his fairly lazy play. I purchased more and his activity resumed. I am a true believer! He is 4.5 now and I will continue to give it to him as long as he lives.