Will Falconer, DVM Moderator
Hi Cathy,
I can't point you to it, but we've known this for a very long time. Mom passes on passive immunity in her colostrum to those things she's been exposed to. Passive means temporary, and not active, which would happen when the youngster is exposed and responds with his own immune system.
The passive immunity gets the youngster by for a few months, maybe up to 4, before it subsides and Junior is on his own. It's that same immunity that prevents vaccines from working if given too early to a youngster.
Good question. Glad you're thinking critically.