We are not the only ones that can feel under the weather, especially during the winter period. Dogs also catch colds and feel unwell. They also happen to be good at not showing that something is wrong, too, until something is really wrong. Don’t be surprised if you hear your dog sneezing or being unhappy to play today compared to yesterday, for example. But is there a way to help them? In other words, how do you strengthen a dog’s immune system?