I think a good indicator would be how well the animal thrives and produces. A suffering animal will not thrive or produce well. Cow comfort can be the culprit and farmers will readily accommodate their cows when we point out the difference it can make. In the same vein, I have often seen ads looking to hire exclusively women to milk cows because the general perception is that women milkers handle the cows more gently and the cows thus have less stress and produce better. To briefly address some of the specific points Richard mentions.
Cows are funny.
The excrement of another dog. It is important not to be too anthropomorphic when trying to determine what is normal for animals. Where does it say that animals must be exposed to members of the opposite sex or have intercourse with them. AI sure cuts down on the incidence of venereally transmitted diseases. It also permits certain manipulation for the benefit of man and beast.