Not sure why you think birth defects on animals and children are so funny. Since I see animals everyday that have life affecting underbite, even a Brewer's Blackbird last week with a short upper bill, I don't find underbite or any other birth defect to be anything to laugh about. The populations of many of the wild species whose young are born with underbite or overbite are in decline. That isn't funny either.
A book was published in 2018 by a veterinarian in Mexico who found that a high prevalence of the Brahman cattle he saw on a regular basis were born with an underbite or an overbite. It was so common there, he even invented a tool to measure the bite on cattle and other ruminants. Interestingly, Mexico allows the use of imidacloprid, a neonicotinoid insecticide that was found by a study done in South Dakota on white-tailed deer and published in Nature to cause shortened jaw bones resulting in either underbite or overbite, depending on which jaw bones were underdeveloped.