CANINE REPRODUCTION
Estrous cycle
Dogs enter puberty anywhere from 6 months to 2 years of age. Larger dogs enter puberty later than do small breed dogs. Bitches cycle on average every 7 months.
The stages of the estrous cycle are defined below:
| Stage | Physical changes | Vaginal cytology | Behavior | Endocrinology |
| Proestrus | Vulvar swelling, serosanguinous vulvar discharge | Increasing cornification | Male interested but bitch will not stand | Estrogen high, progesterone rising |
| Estrus | Vulva less turgid, straw-colored vulvar discharge | 100% cornification with > 50% anuclear squames | Bitch will allow male to mount and breed - "standing heat" | LH peak occurs on average the second day of estrus, progesterone rises |
| Diestrus | No physical changes | Abrupt return to non-cornified smear | Bitch will no longer stand to be bred | Progesterone high regardless of pregnancy status |
| Anestrus | --- | --- | --- | --- |
Breeding management
Optimal breeding day is 2 days after ovulation. Breeding management is best performed by measurement of progesterone in serum, following the 2-2-2 rule = a progesterone concentration of 2 ng/ml indicates ovulation in 2 days and optimal breeding day (for litter size) is 2 days after that.
Pregnancy diagnosis
- Palpation - days 28-35 of pregnancy
- Ultrasound - days 25 to parturition - best technique for assessment of fetal
viability
- Relaxin assay - days 28 to parturition
- Radiography - day 42-45 to parturition - best technique for assessment of
litter size
Gestation length = 63 days from ovulation, 58-71 days from a single breeding
Pregnancy termination
Estrogen mismate shots can be given at the time the bitch is bred and are effective if given after ovulation but before the bitch goes into diestrus. Negative side-effects of estrogen therapy include idiosyncratic pancytopenia and pyometra. Prostaglandin F2-alpha (Lutalyse) is the drug of choice. It can be used safely and effectively anytime from day 5 of diestrus through parturition. Side-effects are transient and include vomiting, diarrhea and hypersalivation.
Eclampsia
= hypocalcemia. Most common in small breed dogs nursing a large litter. Clinical signs are mydriasis, hyperthermia, muscle fasciculations, disorientation and ataxia. Convulsions and death may occur. Treat with IV calcium while ausculting the heart. Discharge with oral calcium / Vit D therapy for the duration of the lactation.
Pyometra
Pyometra (pyo = pus, metra = uterus) has a two-step pathogenesis. Repeated estrous cycling of the bitch, with repeated exposure to estrogen followed by progesterone, causes development of cystic endometrial hyperplasia (CEH). Opportunistic infection of vaginal flora occurs during estrus, when the cervix is open. E. coli is the most common infectious organism involved. Diagnosis is by demonstration of uterine enlargement, abdominal distension (if cervix closed) or purulent vulvar discharge (if cervix open), and neutrophilia. Secondary azotemia may occur due to dehydration and renal disease subsequent to endotoxemia. The best treatment in all cases is ovariohysterectomy. Medical therapy with antibiotics and prostaglandin may be attempted in some cases.
Mammary neoplasia
Mammary neoplasia in bitches may be malignant (adenocarcinoma, 50%) or benign (fibroadenoma, 50%). Incidence is greater in dogs aged > 5 years than in young bitches and can be greatly reduced by spaying bitches before they go through estrus. Treatment is surgical removal.
Cryptorchidism
All dogs have two testes (no monorchid dogs have been reported). Dogs that do not have two scrotal testes by six months of age are cryptorchid. The retained testis may be in the inguinal area or in the abdomen. Retained testes do not produce spermatozoa but do produce testosterone. Retained testes are more likely to become neoplastic than are descended testes. Cryptorchidism is hereditary in dogs. Bilateral castration is recommended in all cases.
Testicular neoplasia
The three most common types of testicular tumors in dogs are Sertoli cell tumor, seminoma and interstitial (Leydig) cell tumor. All occur with equal frequency in scrotal testes. Metastasis is uncommon and castration is curative. A paraneoplastic syndrome, due to estrogen production, may be seen with Sertoli cell tumors, and includes gynecomastia and attraction of male dogs.
Prostate disease
The three most common prostate disorders of dogs are benign prostatic hyperplasia (BPH), prostatitis and prostatic neoplasia. BPH is a normal aging change but may be associated with hematuria, hemospermia, dripping of bloody fluid from the penis unassociated with urination or constipation. Castration is the treatment of choice. Prostatitis occurs secondary to either BPH or neoplasia. Treatment is antibiotic therapy and treatment for the underlying cause. Prostatic neoplasia in dogs is always malignant adenocarcinoma and it has metastasized by the time of clinical presentation. Treatment is palliative.
Brucellosis
Brucella canis - Test with the rapid slide agglutination test, which is sensitive but not specific; all positives must be rechecked, ideally with the AGID test from Cornell. Clinical signs are late gestation abortion in bitches, infertility, epididymitis. Antibiotic therapy is not curative.