However, it's important to note that:
* This is just an average. Some litters may have as few as 1 or 2 puppies, while others can have up to 10 or more.
* The number of pups can be influenced by several factors, such as the mother dog's age, health, and size, as well as the father dog's genetics.
* It's impossible to predict the exact number of puppies in a litter.
If you're interested in breeding Jack Russells, it's essential to consult with a veterinarian and a reputable breeder to ensure responsible breeding practices.