@tanza I agree, smaller isn't a runt. Abnormally small is a runt.
I have never seen stats on runts in basenjis. But I do know they've done research on runts and conception times.
Bitches release eggs once. So yes, you could have fertilization 24 hrs difference, but not much more. Research shows that it has very little impact.
Runts often are ones with genetic/health issues, or placement issues, and sometimes failure to get colostrum in the critical first 4 hrs or even 12, making them open to infections that can slow growth (and is a part of many fading puppies).
"Why do litters have runts?
A dog’s uterus is Y-shaped, and the puppy that develops in the middle of the uterus is normally the farthest from the mothers blood supply and receives fewer nutrients.
So, in a sense, the puppy in the middle is “eating” less than the others, which leads to smaller size, less strength, and in some cases, even health problems."
"Was the Runt Conceived Later Than His Littermates?
Probably not. Runt puppies most likely are the same age as their littermates but had poor placentation. Bitches release all their eggs over a 24-hour span. Even if the conception of that small pup occurred later than conception of the other puppies, all pups float around free for 17 days before implantation and formation of the placenta."
Margaret V. Root Kustritz, DVM, Ph.D, DACT, professor of small animal reproduction at the University of Minnesota
"here’s a common misconception that runts are conceived later than their full-sized litter mates, so effectively they’re born prematurely.
Whilst it is possible for puppies within a litter to be sired by more than one father, the eggs fertilized later catch up with the other embryos quickly in the very earliest stages of pregnancy....A runt puppy might have failed to develop quickly enough because of a congenital defect which impeded their growth.
Or their placenta might have embedded in an unfavorable spot on their mum’s uterus, so they didn’t get quite as many nutrients as they needed from her."