UAP Mutilations, Why Humans and Cattle ?

I believe Col. Phillip Corso gave the answer to it in the interview that was released on Weaponized .

Cattle are noted in biomedical research for their remarkably similar reproductive cycle to humans and are therefore very useful in research in the female reproductive system.

The use of cattle in reproductive biology is especially popular, in fact, they are considered the best model for studying human reproduction. They have particularly similar reproductive cycles to humans which make them ideal models.

Source : https://www.understandinganimalresearch.org.uk/what-is-animal-research/a-z-animals/cattle