older male chi with new lab puppy

Question
we recently purchased a female choc lab, and we have a male chi 5 yrs who is
not yet neutered, our lab is only 14 weeks old,-we have had them together
for 6 weeks- but our chi has within the last week taken a huge interest in her
anus, and will not leave her alone sniffing her constantly ...she can't be
coming into her heat yet she is only 3.5 months and i thought they can start
their heat at 6 mo....is this typical behavior because he is a male & she is a
female? thanks

Answer
This isn't a criticism, but I think that I would have neutered a dog that old before getting a puppy.  This is just a thought and I'm not alleging anything, but when many unethical breeders sell Chihuahuas, they try to pass them off as being younger than they are so as to secure more money for the (falsely called) "teacup" Chihuahuas.  While you say your Lab is 3.5 months old, technically, a dog can go into heat when younger than five months.  My experience is with Chihuahuas and they can go into heat at five months of age.  So, if your breeder (and I'm not saying this happened) happened to sell a litter kind of late and claimed that they were 10 weeks old when they were actually 14 weeks old (sometimes breeders of larger dogs will try to sell pups that look like they'll be larger for greater sums of money when the pups are actually older than said), then there's a possibility of a pup being older than thought and actually going into heat.

That being said, I also want you to consider something else.  When a puppy or dog defecates, there is a gland (anal gland) that empties when firm stools press against it.  You don't usually see problems with pups, but you can.  It depends on the pup, if it's been wormed and the type of food it has been on.  Has the pup been wormed?  What are you feeding it?  What are the stools like?  Your male Chihuahua could simply be interested in the smell of the anal gland that isn't expressing properly.

Get back to me with answers to the above questions and let's talk about this more.

Jo Ann