dogs licking

Question
i have a 3 year old jack russell and an 18 month old labrador. Recently i've noticed the jack russell licking the labradors penis and anal area all the time. He always tries to hump him too. i even found him licking the labradors poo. why is he suddenly behaving like this? is their somthing medically wrong with either of them, is it hormonal

Answer
While most likely it is hormonal, it wouldn't hurt to have them both checked.  Dogs' personalities keep changing until they mature at 3 years old.  Exactly why the JRT is reacting to that as he is is hard to say.  I am sure if they aren't neutered, doing so would reduce it.  It is no cure all, but makes a big difference.