Well if you want an explanation about the kidney failure, here it is.
When introducing a foreign body into a new one, there's always a chance of an allergy as a reaction. A common allergy that can develop is a semen/vaginal fluid allergy for either the human or the animal. Even saliva can cause this, any bodily fluid really. Severe enough reactions can cause anaphylaxis. It may not be detectable outside just by looking at an animal, but allergies for animals tend to attack the internal organs. I had a cat allergic to beef and chicken and we didn't discover how much damage it was doing until she had an xray done at a vet visit. We would have never known if it weren't for that.
Kero, forcing himself on his dog more than likely put the dog in anaphylaxis. From what I understand, the dog died young for his breed due to kidney failure. Kidneys, along with the stomach and liver are often the targets of allergens and are damaged the most due to being in contact with the digestive system. Anaphylaxis doesn't always result in the throat closing and seizures, it can lurk in the background, slowly poisoning a person over time. Getting worse and worse the more the allergen in introduced.
In other words, Kero gave his dog an allergy, and by constantly fucking the dog it allowed an allergy to elevate into anaphylaxis and destroy the dog's kidneys during the poor thing's short life.
