Reproductive System

The reproductive system provides the mechanism for the recombination of genetic material that allows for change and adaptation. Manipulation of this system in breeding management programs allows the rapid and dramatic alteration of the conformation and productivity of domestic animals. Theriogenology is the veterinary clinical specialty that deals with reproduction.

Sex determination of the gonads is important for development of the sex phenotype (internal and external genitalia, secondary characteristics) and sexual behavior. A sex chromosome genotype of XY leads to the development of testes due to the sex-determining region of the Y chromosome (SRY) gene. The SRY gene induces downstream factors such as SRY-box containing gene 9 (SOX9), anti-Müllerian hormone, and glial cell line–derived neurotrophic factor in Sertoli cells.

Abortion is the termination of pregnancy after organogenesis is complete but before the expelled fetus can survive. If pregnancy ends before organogenesis, it is called early embryonic death. A dead, full-term fetus is a stillbirth (its lungs are not inflated). Many etiologies of abortion also cause stillbirths, mummification, and weak or deformed neonates.

Bovine genital campylobacteriosis is caused by either Campylobacter fetus venerealis or C fetus fetus. Clinical signs include irregular estrous cycles, prolonged breeding seasons, and occasional abortions. A vaginal mucus agglutination test can be used for diagnosis but requires sampling multiple cows. Outbreaks can be controlled by vaccination or artificial insemination.

Brucellosis is caused by bacteria of the genus Brucella and is characterized by abortion, retained placenta, and to a lesser extent, orchitis and infection of the accessory sex glands in males. The disease is prevalent in most countries of the world. It primarily affects cattle, buffalo, bison, pigs, sheep, goats, dogs (see Brucellosis in Dogs), elk, and occasionally horses. The disease in people, sometimes referred to as undulant fever, is a serious public health problem, especially when caused by B melitensis.

First recognized in Italy more than 200 years ago, contagious agalactia is primarily a disease of dairy sheep and goats and is characterized by an interstitial mastitis leading to a loss of milk production, arthritis, and infectious keratoconjunctivitis. It is more often seen on farms practicing traditional husbandry. Contagious agalactia is principally caused by the wall-less bacterium Mycoplasma agalactiae, but in recent years, M mycoides capri (Mmc; formerly known as LC), and, to a lesser extent, M capricolum capricolum (Mcc) and M putrefaciens have also been isolated from goats with mastitis, arthritis, and occasionally, respiratory disease. The clinical signs of these infections are sufficiently similar to those of contagious agalactia for the OIE to include them as causes of this listed disease.

Among domestic animals, cystic ovary disease (COD) is most common in cattle, particularly the dairy breeds, but it occurs sporadically in dogs (see Follicular Cysts in Small Animals), cats, pigs, and perhaps mares.

Equine coital exanthema is a benign venereal disease of horses caused by equine herpesvirus type 3. Clinical signs include multiple, circular, red nodules on the genitalia of both mares and stallions. Diagnosis is based on clinical signs and can be confirmed by identifying the virus histologically. There are no vaccines or specific treatments. Sexual rest is recommended to allow lesions to heal and prevent spread.

Mastitis, or inflammation of the mammary gland, is predominantly caused by bacterial pathogens and occasionally mycotic or algal microbes. Pathologic changes to milk-secreting epithelial cells from inflammation decreases function, ie, milk production. Depending on the pathogen, deceased milk production may continue into further lactations, which reduces productivity and, for beef and other meat-producing animals, potential weight gain for suckling offspring. Although most infections result in subclinical local inflammation or mild clinical cases, more severe cases can lead to agalactia or even profound systemic involvement, including death.

In all species, acute puerperal metritis occurs within the first 10–14 days postpartum. It results from contamination of the reproductive tract at parturition and often, but not invariably, follows complicated parturition. Important causative organisms in cattle include Escherichia coli and Trueperella (Arcanobacterium) pyogenes, but culture-independent studies have demonstrated the dominant role of gram-negative anaerobic bacteria such as Prevotella melaninogenica and Fusobacterium necrophorum. The condition is usually acute in onset. Affected cows, mares, ewes, does, or sows are depressed, febrile, and inappetent. A fetid, watery uterine discharge is characteristic of the condition in cows but may not be conspicuous in other species. Milk production is diminished, and nursing young may show signs of food deprivation.

Two common and distinct forms of posthitis and vulvitis are recognized in small ruminants. The first, referred to as enzootic posthitis and vulvitis, is associated with high-protein diets, infection with Corynebacterium renale or other urease-producing organisms, locally high concentrations of ammonia, and severe posthitis. The second is referred to as necrotic or ulcerative balanoposthitis and vulvitis. Its cause is unclear, but Mycoplasma mycoides mycoides is implicated, as are other Mycoplasma spp organisms of the Histophilus/Haemophilus group, and potentially viruses, such as caprine herpesvirus 1.

Numerous etiologies or pathophysiologies can be involved in this syndrome, which is reflected by the use of several different names—mastitis-metritis-agalactia (MMA) complex, agalactia syndrome, dysgalactia syndrome, mammary edema, periparturient hypogalactia syndrome, agalactia toxemia, and puerperal mastitis. However, these names are not synonymous and have often been misused. The syndrome can currently be classified according to the number of mammary glands affected, ie, uniglandular or multiglandular mastitis (including postpartum dysgalactia syndrome [PPDS], MMA complex). (Also see Mastitis in Large Animals.)

Parturition is induced by the fetus in both cattle and sheep. It is initiated by rising cortisol levels in the fetus that provoke a cascade of endocrine activity in the dam. Fetal cortisol increases as a result of increased adrenocorticotropic hormone (ACTH) production by the maturing fetal pituitary caused by fetal stressors such as hypoxia and hypercapnia. Gestation length is unique to each fetus, but approximate gestation lengths can be ascribed to each species (see Table: Approximate Gestation Periods).

Pseudopregnancy in goats most often affects older, parous does. The primary clinical sign is hydrometra, accumulation of fluid within the uterus. The condition can be diagnosed by ultrasonography or by finding low levels of pregnancy-associated glycoprotein. Treatment is a luteolytic dose of prostaglandin F2alpha.

Retention of fetal membranes, or retained placenta, usually is defined as failure to expel fetal membranes within 24 hr after parturition. Normally, expulsion occurs within 3–8 hr after calf delivery. The incidence in healthy dairy cows is 5%–15%, whereas the incidence in beef cows is lower. The incidence is increased by abortion (particularly with brucellosis or mycotic abortion), dystocia, twin birth, stillbirth, hypocalcemia, high environmental temperature, advancing age of the cow, premature birth or induction of parturition, placentitis, and nutritional disturbances. Cows with retained fetal membranes are at increased risk of metritis, displaced abomasum, and mastitis.

Seminal vesiculitis is inflammation and/or infection of one or both vesicular glands. Signs may include purulent material contaminating bull semen. Diagnosis often occurs during a breeding soundness examination through manual rectal palpation or visible observation with rectal ultrasound of enlarged seminal vesicles. Treatment includes broad-spectrum antibiotics to control local infection and NSAIDs to reduce inflammation. Bulls with persistent or recurring seminal vesiculitis are considered unsatisfactory breeders and should be culled.

Trichomoniasis is a venereal disease of cattle characterized primarily by early fetal death and infertility, resulting in extended calving intervals. Distribution is likely worldwide. Diagnosis is confirmed by isolation of the organism. Imidazoles have been used to treat infected bulls, but none is both safe and effective. Control is by culling infected bulls.

Also see Mastitis in Large Animals and Pseudocowpox.

Prolapse of the uterus may occur in any species; however, it is most common in dairy and beef cows and ewes and less frequent in sows. It is rare in mares, bitches, queens, and rabbits. Invagination of the tip of the uterus, excessive traction to relieve dystocia or retained fetal membranes, uterine atony, hypocalcemia, and lack of exercise have all been incriminated as contributory causes.

Eversion and prolapse of the vagina, with or without prolapse of the cervix, occurs most commonly in cattle and sheep. A form of vaginal prolapse, different in pathogenesis, also occurs in dogs (see Vaginal Hyperplasia in Small Animals). In cattle and sheep, the condition is usually seen in mature females in the last trimester of pregnancy. Predisposing factors include increased intra-abdominal pressure associated with increased size of the pregnant uterus, intra-abdominal fat, or rumen distention superimposed upon relaxation and softening of the pelvic girdle and associated soft-tissue structures in the pelvic canal and perineum mediated by increased circulating concentrations of estrogens and relaxin during late pregnancy. Intra-abdominal pressure is increased in recumbent animals. Added to this, sheep tend to face uphill when lying down, so gravity contributes to vaginal eversion and prolapse. Docking the tails of lambs may damage structures that support the pelvic girdle (eg, coccygeus muscle) and predispose to vaginal prolapse if the tail is docked too short. The tail should be removed at the level of the ventral skin fold, leaving two or three coccygeal vertebrae intact.

Contusion and hematoma of the vagina are noted infrequently after parturition in all species but particularly in mares and sows. Occasionally, vaginal hematomas in sows may rupture and cause serious (or fatal) hemorrhage that can be controlled by ligation of the labial branch of the internal pudendal artery. Necrotic vaginitis, vestibulitis, and vulvitis may follow dystocia in all species. Onset of signs, consisting of arched back, elevated tail, anorexia, dysuria, straining, vulvar and perivulvar swelling, and possibly a fetid, serous discharge, begins within 1–4 days of parturition and may persist for 2–4 wk. In most cases, only gentle and conservative treatment is needed. Prophylactic antibiotic treatment is wise, because clostridial or other organisms may proliferate in the damaged tissue and cause tetanus (see Tetanus), blackleg (see Blackleg), or other forms of clostridial myositis. Possible consequences of necrotic vaginitis include permanent stricture of the vagina, transvaginal adhesions, or perivaginal abscessation.

Also see Management of Reproduction: Dogs and Cats.

Also see Management of Reproduction: Dogs and Cats and Prostatic Diseases and Congenital and Inherited Anomalies of the Reproductive System and Infertility in Dogs and Cats.

Although dogs occasionally become infected with Brucella abortus, B suis, or B melitensis, these sporadic occurrences typically are closely associated with exposure to infected domestic livestock (see Brucellosis in Large Animals).

Tumors arising from mammary tissue are commonly observed in older, intact female dogs and cats. A mammary tumor is usually suspected on detection of a mass during physical examination in the caudal abdominal and cranial thoracic mammary glands (in dogs and cats, respectively). The diagnosis is confirmed by histopathology and is important for determining treatment and prognosis. Surgical removal of the tumor with the regional lymph node will increase disease-free time but, in cases of malignancy, may not increase survival time.

Disease of the prostate gland is relatively common in intact dogs but less common in other domestic animal species. Benign prostatic hyperplasia is by far the most common disease of the prostate in intact male dogs. Bacterial prostatitis (acute or chronic), prostatic abscesses, prostatic and paraprostatic cysts, and prostatic adenocarcinoma are seen much less frequently and can be seen in castrated males.

Canine transmissible venereal tumors (TVTs) are cauliflower-like, pedunculated, nodular, papillary, or multilobulated in appearance. They range in size from a small nodule (5 mm) to a large mass (>10 cm) that is firm, though friable. The surface is often ulcerated and inflamed and bleeds easily. TVTs may be solitary or multiple and are almost always located on the genitalia. The tumor is transplanted from site to site and from dog to dog by direct contact with the mass. They may be transplanted to adjacent skin and oral, nasal, or conjunctival mucosae.