Thank you for feeding on its belly upright, as it would be up against a nursing momcat, not on its back drinking from a bottle. Ir'a not the bottle that is the problem, but the kitten's position while drinking/nursing. Kittens ahould not be in the same position as a human baby on its back drinking from a bottle.
Its only common sense to learn how to take care of abandoned cats before you start taking them in, we work for many years together with a catsaving organization. 😻
