POTENTIAL USES

Clinical examination of reproductive organs is useful to confirm infectious and noninfectious causes of reproductive failure (Box 99-1). Presence of physiologic or anatomic abnormalities associated with reproductive failure can be verified or refuted by examination of the female genital organs. Alternately, findings on these examinations may clearly illustrate shortcomings in breeding management.

Reproductive slaughter checks also can be used for collection of specimens for diagnostic procedures. Fetuses, uteri, oviducts, urinary bladders, and kidneys are readily obtained for histopathologic examination or the procurement of culture swabs. To adequately assess the significance of lesions or other abnormalities, it is imperative that veterinarians have sufficient understanding of normal ovarian and uterine structures.

SPECIMEN COLLECTION TECHNIQUES

Procedures at the Slaughterhouse

Reproductive and urinary tracts are examined at the slaughterhouse or removed to a clinic or laboratory with appropriate approval from regulatory officials. Individual identification of animals at slaughter is used to correlate gross and histologic findings with the reproductive history of the sow. Ear tags are convenient, but ear, shoulder, or flank tattoos constitute a more reliable means of identification.

It is beneficial to examine other body systems while animals are being processed in the packing plant. Body condition and backfat thickness of animals are assessed after evisceration. Hence, additional information is gathered to assist in the interpretation of the cause(s) of reproductive failure. Abnormalities, such as acyclic ovaries, actually reflect suboptimal management of the breeding herd. For example, the absence of backfat on sows during the summer and early autumn months may reflect inadequate feed consumption or facility cooling systems. These shortcomings in management probably contribute to the pathologic conditions noted in the reproductive organs.

If specimens are to be transported to a laboratory, individual sow identification should be included with each specimen. Specimens are placed in sealed containers and packed in ice for transport. It is imperative to tie the cervix and the neck of the bladder closed with heavy string to prevent contamination or leakage.

Initial Procedures and Gross Examination

Gross lesions are noted on examination of the ovaries, oviduct, uterus, cervix, vagina, urinary bladder, and kidneys. If an infectious etiology is suspected, culture swabs are procured using aseptic technique from both horns of the uterus, urinary bladder, and kidneys. Failure to use aseptic technique usually results in gross contamination of the swabs and erroneous culture results. Urine is obtained by centesis with 20-gauge needles and stored on ice (5° C) for transport to the laboratory. Storage of urine for more than 12 hours limits the diagnostic value of the specimen.¹ Owing to the broad spectrum of bacterial agents involved in urogenital infections,² swabs are submitted for culture under aerobic and anaerobic conditions. Determination of bacterial sensitivities to antibiotics also should be requested for future reference.

After collection of swabs for bacterial cultures, the vagina, cervix, and each horn of the uterus are incised to allow adequate assessment of the mucosa and luminal contents. The urinary bladder and kidneys also are dissected to examine the bladder lumen and renal pelvis, respectively. To complete the evaluation, it is imperative to collect tissue samples from representative organs for subsequent histologic examination. These samples are fixed in either 10% buffered formalin or Bouin’s solution and submitted for histologic preparation and evaluation. If the diagnostic tests may require special handling, storage, or shipping of tissue, it is beneficial to contact the diagnostic laboratory before collection of samples.

NORMAL MORPHOLOLGY

Normal Ovarian Structures

The possibility of errors in the recording of a sow’s reproductive history make it necessary to determine the stage of the estrous cycle during gross examination of the ovaries. In addition, interpretation of uterine morphologic features is improved when the stage of the estrous cycle is known. The estrous cycle of the pig typically ranges from 17 to 25 days. Owing to this variation in the length of the estrous cycle, it is more convenient to classify the cycle into three distinct phases; proestrus (follicular phase), estrus (sexual receptivity), and diestrus (luteal phase).

Follicle Growth and Ovulation

Ovarian follicles destined for ovulation grow from approximately 4 to 5 mm in diameter on day 15 (day 0 = the first day of standing estrus) of the estrous cycle to an ovulatory diameter of 8 to 12 mm (Fig. 99-1). Preovulatory follicles have taut, almost transparent walls and contain straw-colored fluid. Estrogen (17β-estradiol), the predominant ovarian hormone produced at this time, contributes to estrous behavior and to morphologic changes in the reproductive tract and triggers the surge of luteinizing hormone (LH) from the anterior pituitary gland.

Fig. 99-1 Large, fluid-filled follicles are evident on the ovaries of a sow during proestrus. The corpora lutea are well regressed and white-yellow in color.

The LH surge is necessary to induce ovulation or rupture of the follicles with the subsequent release of ova. Onset of estrus usually coincides with the preovulatory LH surge; depending on age, females may be sexually receptive for 1 to 3 days. Ovulation occurs in most gilts during the latter part of the second day after the onset of estrus; however, the time between the onset of estrus and ovulation varies considerably among sows.

Luteal Structures

After ovulation, collapsed follicles are 4 to 5 mm in diameter. Blood rapidly fills the central cavity of the follicles. At this stage, these blood-filled structures are considered corpora hemorrhagica. Luteinization of the follicular remnants results in the formation of multiple corpora lutea. By day 5 to 6, each corpus luteum (CL) has reached its mature diameter of 9 to 11 mm, and the central cavities are completely replaced by luteal tissue (Fig. 99-2). The corpora lutea produce the steroid hormone progesterone. Serum progesterone concentrations, detectable within 1 to 3 days after estrus, increase until a maximum is achieved during mid- to late diestrus.

Fig. 99-2 A, Ovaries collected from a sow at 1 to 2 days after ovulation. The blood-filled structures are corpora hemorrhagica. B, Mature corpora lutea are evident on the ovaries of a sow during diestrus.

Degeneration of the corpora lutea commences at approximately day 13 to 15, coinciding with increased concentrations of the luteolysin prostaglandin F₂_α (PGF₂_α)³ and decreasing concentrations of progesterone. It is assumed that PGF₂_α contributes to regression of the corpora lutea; however, other factors evidently influence the structural regression of the corpora lutea. Obvious indications of CL regression are the change in color from reddish-pink to yellow and a gradual decrease in diameter. A new wave of follicular recruitment commences on days 13 to 15, with follicle enlargement and hyperemia obvious by day 17 (Fig. 99-3). Follicles continue to enlarge concomitant with regression of the corpora lutea.

Fig. 99-3 Ovaries collected from a sow that was in late diestrus to early proestrus. The corpora lutea are beginning to regress. By contrast, growth of follicles has commenced, and follicles are approximately 5 mm in diameter.

With maternal recognition of pregnancy (occurring on days 10 to 14 after ovulation and successful mating),⁴ CL lifespan is extended throughout pregnancy. The gross appearance of the corpora lutea of pregnancy (Fig. 99-4) is remarkably similar to that of the corpora lutea during diestrus. Dissection of the uterus will reveal fetuses if the animal’s pregnancy had progressed to 20 days of gestation or later. Before 20 days of gestation, it is useful to flush both horns of the uterus to detect the presence of early embryos. Confirmation of pregnancy status is particularly applicable when the quality of matings or estrus detection requires scrutiny or when records of these events are not maintained in an orderly and detailed fashion. It is not uncommon to observe pregnancies in animals that were erroneously recorded as anestrous. These observations illustrate weaknesses either in the record system or in management practices.