Fetuses will normally only be resorbed if they die during the first 1/2 of the pregnancy. It is possible for a bitch to resorb only some fetuses while others go on to be born.
The most common causes of fetal resorption are inadequate progesterone levels in the bitch, maternal infectious disease (such as brucellosis and canine herpesvirus), endometrial disorders, developmental defects in the fetus (unlikely to affect a whole litter).
Testing progesterone levels in the bitch can be done after estrus even if she isn't bred, due to the persistance of the corpus luteum in bitches. This is convenient, since you don't have to breed her in order to test for this problem. A complete physical exam with a general blood panel is a good idea. Testing for brucellosis and canine herpesvirus might be useful, although most bitches who lose litters to herpesvirus will have normal subsequent litters. Bacterial cultures of the vagina may be useful and in some cases uterine biopsy will be necessary to diagnose a problem.
There are reproductive specialists in veterinary medicine, known as theriogenologists. They can usually be found at veterinary schools.
Mike Richards, DVM


