Missed breedings can be frustrating and disheartening, especially when they occur after months or even years of planning. Several factors play a role in a successful breeding, and understanding each can increase your chances of a litter of puppies in the future.

Semen Quality

Sometimes dogs have low-quality sperm, especially as they enter their senior years. Have the dog's sperm evaluated for quantity, motility and any abnormalities.

Ovulation

Females ovulate anytime from day five of their season to day 21. Progesterone testing can pinpoint the ovulation date, which will greatly increase the chances of a pregnancy.

Timing of Breeding

Once ovulation occurs, the eggs require 48 hours to mature before they can be fertilized. Breeding too early or too late will result in a missed breeding.

Fertilization

If the sperm doesn't reach the egg, fertilization will not occur. Outside ties, where the male is not "held" in place by the female, and improper artificial insemination procedures are a common culprit. Some females, especially older ones, may have cysts within the uterus that prevent the sperm from reaching the eggs.

Implantation

Fertilized eggs do not implant in the uterine wall until 17 to 18 days after ovulation. Bubbling or thickening of the uterine lining can prevent implantation.

Pregnancy Maintenance

Problems with the uterine lining can also prevent placental growth, which causes absorption of the embryos. Genetic defects, viruses and toxins may also cause absorption or spontaneous abortion.

Source:

VeterinaryPartner.com: Transcript: Canine Reproduction Seminar

More Information:

American Kennel Club: A Guide to Breeding Your Dog