Among certain mammals like deer, during the rutting season, female deer may be courted by multiple male deer. The males with larger antlers (which could be analogized to the 'huge cock' in a very different sense) may seem to have an advantage in attracting the female. However, the female may not be strictly monogamous and could mate with different males. This is more about the natural selection and reproductive success in their species rather than any human - like concept of cheating.
Well, take peacocks for instance. The female peacock may seem to be 'flirting' with multiple male peacocks. The male peacocks display their huge and colorful tails to attract the female. Sometimes the female might choose to mate with more than one male in a season. This could be seen as a form of behavior that might be related to a 'cheating' concept in a very loose way, as she is not being exclusive to one male, while the male's large and showy features play a role in this complex mating behavior.
In the animal kingdom, some species might seem to have behaviors that could be misconstrued as 'cheating'. For example, female birds may sometimes mate with multiple males. But this is often more about ensuring genetic diversity for their offspring rather than what we consider 'cheating' in a human moral sense. There are also some fish species where females may accept sperm from different males during spawning, which is a natural part of their reproductive strategy.