What type of animals can use Miracle Vet weight gainer? Matthew Kinneman February 17, 2018 14:25 Updated Follow Miracle Vet weight gainer isn't just for dogs. It's also suitable for cats and livestock. You can start using Miracle Vet at 4 weeks of age. It's also safe to use year round. Related articles Do Miracle Vet results last? What age does my dog need to be in order to use Miracle Vet? How much weight will my dog gain when using Miracle Vet? Is Miracle Vet safe? Comments 0 comments Please sign in to leave a comment.