No commercially made supplement marketed for increasing fertility in dogs or bitches has ever been tested and proven effective in increasing fertility. Individual ingredients that have been shown to support sperm function include fish oil, Vitamin E, Zinc, L-carnitine, and Perna mussel. For both bitch and dog, your best strategy is to feed an appropriate, well-balanced diet, such as those made by Hill’s, Purina, or Royal Canin. Each of these companies conducts research into their diets, including feed trials.