The support of immune development in animals is significant for the maintenance of animal health and production, which is of vital importance to the food industry. A balanced diet, a hygienic environment, health management strategies such as biosecurity and vaccination, and natural feed additives such as essential oils (EOs) can all contribute to the development and maintenance of a robust immune system in animals. Some EOs have antimicrobial activity, support respiratory and mucosal health and have an immunomodulatory effect that can help animals resist infection and disease and improve their overall health and well-being.