When discussing pregnancies, and reproductive cycles, we need to understand that bitches are not humans in their physiology - with all respect to Vilma and her knowledge of human reproduction (hi there!). And bitches are not little cows, either. So much of the knowledge of animal husbandry we know from animals other than bitches, does not apply to bitches! We do know that the health and nutrition of any animal is important in reproduction. And we need to remember that it's the timing of the breeding, genetics, and the *health of the uterus* that determine litter size.
I plead ignorance about human ovulation. But a bitch is the only domestic animal whose ova are ovulated into a progesterone environment, not the estrogen environment of other animals. And a bitch ovulates an immature egg that requires further division before fertilization can occur. A fertilized egg implants in the uterus at Day 17-18. Whether or not a bitch is in fact bred and becomes pregnant, or not, when she goes through her cycle, her uterus acts exactly as if it is pregnant. The hormonal levels that change with a cycle change and apply regardless of whether there are puppies. The progesterone levels affecting the uterus each cycle are at the same level, and last as long in the bitch, whether she is bred or not. So the uterus is not "rested" or "spared" or "saved" by skipping a cycle. The only difference to the uterus is whether there are puppies in it. If we look at this from a non-anthopomorphic viewpoint, it is healthier for the bitch, and healthier for the uterus - if one wishes to have a bitch produce well - to breed her back to back until you no longer wish to have puppies from her. I know this sounds like heresy to some folks, and I am *not* advocating turning every breeding program in to a puppy mill, so let's not carried away here. If you look at the uterus of the bitch 12 weeks after she whelps a litter, it is usually totally healed, and ready to start the process over again. Actually, it usually does start the process all over again. By Day 16-17 of her cycle, if you didn't breed her, the process starts all over again. Bitches never go into menopause. And when 5 of them all living in the same house come in season in the same week - well, they don't call them bitches for nothing. Libby Kesner and the Berner girls of Maine Voorheesville NY USA
