10/29/2026
👉 Littermate Syndrome 👈
Littermate syndrome is not an officially recognized scientific or medical diagnosis, and there is no single documented date or scientific paper that established its "creation." No single animal behavior school "owns" or exclusively teaches littermate syndrome, because it is not an official, clinical medical diagnosis recognized by veterinary boards like the American College of Veterinary Behaviorists (ACVB).
Instead, it is an anecdotal, informal term popularized by uncertified dog trainers, breeders, and pet owners over several decades to describe a cluster of behavioral issues-such as extreme co-dependence, separation anxiety, and sibling aggression-that can happen when two puppies of the same age are raised together.
“Informal term”
** An informal term is a word or phrase used in relaxed, casual, or everyday speech rather than in serious, official, or academic writing according to the Merriam-Webster Thesaurus. **
🚨 Friendly Reminder 🚨
The “dog training” industry is not regulated and anyone can claim to be one!