From Oregon State University
CORVALLIS, Ore. – A groundbreaking study of more than two dozen rescued dogs, some aggressive and some not, showed a clear link between aggressive 
behavior and the microbes that live in the dogs’ guts.
The findings, published today in PeerJ, stop short of saying the composition of a dog’s gut microbiome causes aggressiveness, or vice-versa – only that there are statistical associations between how an animal acts and the microbes it hosts.