The size difference between the two breeds is not usually a problem, as the male pug's penis is long enough to reach the female Chihuahua's cervix. However, there are some potential risks associated with breeding a pug with a chihuahua, such as:
* Dystocia: This is the medical term for difficulty giving birth. Chihuahuas have a narrow pelvis, which can make it difficult for them to give birth to puppies that are too large.
* Stillbirth: Puppies that are born prematurely or that are too large for the female chihuahua's birth canal may be stillborn.
* Neonatal death: Puppies that are born prematurely or that have a low birth weight may be more likely to die in the first few weeks of life.
If you are considering breeding a pug with a chihuahua, it is important to talk to a veterinarian first to discuss the risks involved and to make sure that both dogs are healthy.