The number you are referring to is the pedigree, which is simply the total of all the possible traits pet can manifest. Each trait is scored according to rarity (1-4). When you breed pets it's random what traits you'll get from each parent's pet pool so you may get a higher or lower pedigree.
The pedigree is slightly misleading in terms of the value of the pet. You could hatch a pet that has better talents than the parents in spite of a lower pedigree.
All this did was make me not want to mix pets anymore, not like I was hoping or wanting to. What is the point of mixing pets, spending the gold to do it, spending the time to train up pets and so on if there isn't any reward or improvement for doing so. I thought the obtained stats would be averaged together, not the initial points. I never expected to have a lower pedigreed pet than my lowest pedigree pet that I mixed. Once again, what is the point?
The Pedigree number is the total number of Rarity Points. If mostly low-RP slots transfer from both parents, the Pedigree could drop below that of either parent. If mostly high-RP slots transfer from both parents, the Pedigree could jump above that of either parent. But, Pedigree number isn't as important as getting the specific abilities you want for the offspring to transfer and manifest.
A Pedigree-55 (22) pet isn't really any better than a Pedigree-52 (22) pet. And a Pedigree-52 (20) pet could be a more useful pet than a Pedigree-55 (22) pet. It depends on the specific abilities that actually manifest.