Abnormalities in fertilization cover the factors that can prevent sperm from reaching the ova. The bitch is still not pregnant just after mating, since gestation has not yet started. In the great majority of cases, failure to fertilize is due to poor calculation of the date for mating, but there may be other causes as well.

Vaginitis

This is an inflammation of the vagina that can occur frequently, although it is rarely diagnosed because the symptoms induced are fairly sparse. The bitch may have a moderate genital discharge, lick her vulva, and be attractive to males even though she is not in heat, or else suffer from repeated urinary infections. Nothing here really points to the cause. Vaginitis, however, is a frequent cause of infertility in brood bitches and, because of this, they should be constantly screened and treated.

Diagnosis is difficult. Although examining the posterior area of the vagina using a speculum or taking vaginal smears can help (one often finds the presence of many white corpuscles or leucocytes), the best procedure consists of inserting a small endoscope into the vagina(vaginoscopy) to examine the exact state of this organ. Local or general treatment with antibiotics needs to be long-term, since these have difficulty in penetrating this organ.

Vaginal deformities

Anatomical deformities of the vagina, such as stenosis or the presence of vaginal hyperplasia during estrus, will generally prevent mating taking place correctly—and this is often how they are detected. Rarely, one can find non development of the deeper part of the vagina (uterine aplasia) or continued existence of the hymen. This might be suspected when a bitch has no discharge during estrus, because obviously the blood from the uterus cannot flow out.

Deformities in the fallopian tubes and uterus

The uterus or fallopian tubes may no longer be permeable to sperm as a result of congenital malformation (segmentation of the genital system, growth defect, etc). In this case, a bitch will be sterile from the start.

However, other deformities can also appear. In the uterus, this is the case, for example, with traumatisms suffered during whelping or with the formation of uterine adhesions due to an incorrectly performed cesarean section. Ultrasound or radiological examinations may help in making a diagnosis. Deformities in the fallopian tubes, whether congenital or resulting from infection, require a hysterosalpingography to be carried out in order to diagnose them correctly, i.e., injection of an opaque substance into the uterus followed by radiographs. In practice, such onerous and complicated procedures are never used on bitches, and the cause of such cases of infertility often remains unexplained.