What type of animals can use Miracle Vet weight gainer? Matthew Kinneman January 17, 2019 22:27 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 How much weight will my dog gain when using Miracle Vet? How fast until I see results when using Miracle Vet? Is Miracle Vet safe? What are the ingredients in Miracle Vet? Do Miracle Vet results last? Comments 0 comments Please sign in to leave a comment.