A sows ability to deliver average and above litter size is one of the important criteria we use to determine her value in our herd. My most recent experience with our largest sow delivering only two piglets led me to inquire with my local vet and do a little research.
One explanation was found in research connecting colostrum intake to future fertility in offspring. Not only does colostrum provide a newborn piglet with additional nutrients needed to survive, it also contains a hormone called relaxin that supports development of the reproductive tract.