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Diagnosis of Pregnancy
Diagnosis of Pregnancy
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Diagnosis of Pregnancy GLEN W. ALMOND
E
arly and accurate identification of pregnant and nonpregnant sows and gilts has a strong potential to increase reproductive efficiency of commercial swine farms. Detection of returns to estrus after mating, ultrasound techniques, and several other methods have been used for pregnancy diagnosis1; however, for various reasons, only three or four techniques currently are used in commercial farms. An ideal pregnancy detection technique is not available, and most producers use either a combination of techniques or one technique that apparently fulfills their requirements. Some methods are restricted to research applications, and it is unlikely that these methods will be adapted for on-farm use. This chapter reviews the techniques for pregnancy diagnosis in swine; the practical applications, or lack thereof, are emphasized for each technique (Table 101-1). For most procedures, sensitivity (ability to detect pregnant animals, representing the proportion of pregnant animals that test positively) and specificity (ability to detect nonpregnant animals, representing the proportion of nonpregnant animals that test negatively) are used to assess accuracy.
• Submissive sows are housed in groups with dominant sows. • Group sizes are too large to permit individual assessments of estrus. • Sows are housed in stalls that do not permit the sow to detect the presence of the boar. • The design of gestation facilities does not allow daily boar exposure to the bred sow. • Breeding herd personnel fail to dedicate sufficient time to estrus detection. • Breeding herd personnel lack adequate training to identify sows in estrus.
HORMONE CONCENTRATIONS Serum concentrations of prostaglandin F2α (PGF2α), progesterone, and estrone sulfate were used as indicators of pregnancy. These hormone concentrations are dynamic, and considerable knowledge regarding endocrine changes in pregnant and nonpregnant sows is required for correct use of these techniques for pregnancy diagnosis. Owing to technical requirements, these methods are not used in the swine industry.
DETECTION OF ESTRUS
Prostaglandin F2a
A common pregnancy detection technique is observation of the sow for failure to return to estrus after mating. This technique is based on the premise that nonpregnant sows will return to estrus within 17 to 24 days after breeding. Detection of estrus is improved if the sow’s behavior is observed in the presence of a boar.2 Thus, this technique requires gestation facilities that are designed to allow daily fenceline contact between boars and sows, or the placement of the boar and sow in the same pen each day. Injections of estradiol or estradiol plus testosterone will enhance estrous behavior in sows that are not pregnant3; however, these steroids are not approved for use in swine in the United States. An early study reported an accuracy of 39% for the detection of return to estrus between 19 and 25 days after mating.4 By contrast, daily estrus detection throughout gestation enabled a 98% accuracy in predicting farrowing rate.5 Albeit rarely seen, a false negative result can be obtained if a pregnant sow shows spontaneous estrus.5 False positive results occur in the following scenarios:
The endometrium of the nongravid uterus secretes PGF2α into the uterine vein between days 12 and 15 of the cycle, thereby inducing regression of the corpora lutea.6 When viable embryos are present, PGF2α is not secreted into the uterine vein.7 The prostaglandin pregnancy test is based on the principle that if serum concentrations of PGF2α are low (less than 200 pg/ml) or undetectable between days 13 and 15 after mating, the sow can be assumed to be pregnant.8 Routine blood sample collection, without the use of indomethacin or other cyclo-oxygenase inhibitors, causes release of PGF2α from blood constituents. This PGF2α release leads to obvious problems with interpretation of serum PGF2α concentrations; however, prostaglandin metabolites are more stable, and serum metabolite concentrations are reasonable indicators of prostaglandin concentrations. The prostaglandin pregnancy test has approximately 90% sensitivity and 70% specificity. Accuracy is lower when animals have delayed returns to estrus, or when fetal death occurs and sows manifest pseudopregnancy. This diagnostic method can be used during early pregnancy, but its unreliability in the detection of nonpregnant animals and the necessity of extensive laboratory procedures limit its practical application.
• Sows become persistently anestrous as a result of cystic ovarian degeneration or inactive, acyclic ovaries, or become pseudopregnant.
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Table 101-1 Applications of Techniques Available for Pregnancy Diagnosis in Swine TIME OF TEST DURING PREGNANCY*
APPLICATION Technique Early pregnancy factor Estrus detection Estrogen injections Laparoscopy Prostaglandin F2α Progesterone Estrone sulfate Rectal palpation Vaginal biopsy Doppler ultrasonography Amplitude-depth ultrasonography Real-time ultrasonography
Commercial
Diagnostic
Research
Ultra-early
X
X
X
X
X X X
X X X X X X X
Late
X X X
X X X X X
Early
X X X X
X
X
X
X
X X X
*Ultra-early: before 18 days after breeding; early: 18 to 24 days after breeding; late: beyond 24 days after breeding.
Progesterone Maintenance of the corpus luteum (CL) is the result of a blastocyst “signal” that is produced at 10 to 12 days after mating.9 The blastocyst-induced maintenance of corpora lutea causes serum progesterone concentrations to remain high (greater than 5 ng/ml) throughout pregnancy. Thus, serum concentrations of progesterone are high in pregnant sows and gilts during the expected time of return to estrus and low (less than 5 ng/ml) in bred sows and gilts that fail to conceive.10 The interestrus interval for sows of various parities ranges from 17 to 24 days, with a mean of 20 to 21 days and a mode of 20 days.11 Therefore, the optimal time to obtain blood samples for progesterone determinations is from 17 to 20 days if nonconceiving sows and gilts are to be identified before the time they return to estrus. The serum concentration of progesterone that most accurately discriminates the nonpregnant from the pregnant sow or gilt has not been determined. Concentrations of 4, 5, 7, 7.5, and 9 ng of progesterone/ml of serum were used to discern pregnancy status5,10; a concentration of 5 ng/ml is most commonly used. The progesterone pregnancy test has greater than 97% sensitivity at 17 to 24 days, but specificity ranges from 60% to 90%.5,12 False positive results are common when nonconceiving sows and gilts have delayed or irregular returns to estrus, and when nonpregnant sows and gilts are anestrous as a result of cystic ovarian disease.5 False negative results may be the result of laboratory error because it is assumed that greater than 4 ng of progesterone/ml of serum is required for pregnancy maintenance in swine.13 Commercial enzyme-linked immunosorbent assays (ELISAs) to measure blood concentrations of progesterone in swine can be used on farms or in veterinary clinics,
thereby reducing the need for laboratory-based radioimmunoassays. The necessity of collecting blood is a significant limitation of this method; however, methods to quantitate fecal progestins were evaluated for monitoring reproductive function in swine,14 dogs,15 and ruminants.16 It was evident that the extraction and assay procedures are feasible alternatives to blood progesterone assays. Despite the potential use of fecal progestin determinations, direct applications of this methodology for pregnancy diagnosis have not gained popularity, nor have they been evaluated on a large scale in commercial pig production.
Estrone Sulfate A high proportion of fetal estrogens is secreted from the uterus into the maternal circulation as estrone sulfate.17 Estrone sulfate initially appears in the maternal circulation at approximately 16 to 20 days and rises linearly to peak levels between 25 and 30 days before decreasing to a nadir at 35 to 45 days.18 A second increase in estrone sulfate occurs concomitantly with increases in other estrogens, commencing at 70 to 80 days and continuing until farrowing. Urinary and serum estrone sulfate concentrations have been investigated for applicability as pregnancy tests.5,19,20 A 10-fold to 100-fold increase in maternal estrone sulfate concentrations typically occurs between 25 and 30 days after coitus in sows that conceive.21 Because estrone sulfate increases during early and late pregnancy, determination of estrone sulfate levels has potential applications as an early pregnancy diagnosis test and as a confirmatory test later during pregnancy. Parity, season, and day of pregnancy when blood was collected have some effect on estrone sulfate concentrations.
Diagnosis of Pregnancy Serum estrone sulfate concentrations greater than 0.5 ng/ml are indicative of pregnancy, whereas concentrations less than 0.5 ng/ml are suggestive of nonpregnant status.5,19 The estrone sulfate pregnancy test has greater than 97% sensitivity and greater than 88% specificity when serum samples are collected between 25 and 30 days of pregnancy.5 False positive results may be attributable to a transient increase of estrone sulfate concentrations in some sows and gilts during proestrus.18 False negative results were obtained in sows or gilts with a premature or delayed rise in estrone sulfate concentrations22 or in sows and gilts that had less than 4 pigs in a litter.5 As with other early tests of pregnancy, animals may be correctly diagnosed as pregnant but subsequently will fail to farrow if the fetuses die after the test has been conducted. Pseudopregnant sows frequently retain the endocrine function of the corpora lutea for prolonged periods and may appear to be pregnant even though they no longer have viable fetuses. Other sows experience loss of their pregnancies, followed by development of acyclic, anovulatory ovaries or cystic ovaries, and similarly fail to show estrus for various time periods. Serum concentrations of estrone sulfate in pseudopregnant animals were similar to those in females that had not been mated and distinctly less than those in pregnant sows.23 Urinary concentrations of estrone conjugates also have been used to predict pregnancy and to diagnose fertility problems.20 for these investigations, urine samples were obtained through the use of vaginal sponges. It should be noted that the glucuronide conjugate of estrone, rather than the sulfate form, was measured; thus, different quantitative procedures were required. Quantitative commercial assay kits for the determination of estrone sulfate concentrations in serum from swine are not available. The need to collect blood (or urine) samples limits the practical application of this technique for pregnancy diagnosis in swine.
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PHYSICAL METHODS Radiography Radiography is a seldom-used method for pregnancy diagnosis in swine. In research studies, it was used after the sixth week of pregnancy,28 when the fetal skeleton begins to calcify. Fetal age, viability, and abnormalities were determined with radiography.29 Equipment costs, potential health hazards to users, and the impracticality of radiography in production facilities render this technique unsuitable for pregnancy diagnosis in commercial swine.
Rectal Palpation Pregnancy diagnosis by rectal palpation of the sow has been demonstrated to be practical and highly accurate.30 Sows in the relevant study were examined while standing in gestation crates or pens, or while tethered. The technique involves examination of the cervix and uterus, together with palpation of the middle uterine artery to assess its size, degree of tone, and type of pulse. Before 21 days of gestation, rectal palpation had a 30% sensitivity, but the sensitivity increased to 75%, 94%, and 100% in animals at 21 to 27, 28 to 30, and 60 days to term, respectively.30 The pelvic canal and rectum often were too small for the procedure to be used on low-parity sows. False positive results were obtained if the external iliac artery or one of its branches was mistakenly identified as the middle uterine artery. False negative results, presumably due to errors in palpation technique or performance of palpation too early, were more common than false positive diagnoses. Despite the potential application of this technique, it has not gained popularity in North America.
Laparoscopy Early Pregnancy Factor Early pregnancy factor (EPF) activity is dependent on the presence of two components: EPF-A and EPF-B. Factor A is formed in the uterus during estrus and pregnancy, whereas EPF-B is produced in the ovary and is associated only with pregnancy. The production of EPF-B is a result of a combined action of endocrine signals from the pituitary and the zygote.24 Serum concentrations of EPF peak 24 to 48 hours after fertilization and exhibit a polyphasic pattern throughout gestation.25 Detection of EPF, based on a rosette inhibition test, is time-consuming and cumbersome and possesses other limitations. Various applications of EPF detection have been proposed for embryo transfer programs and assessment of infertility and early embryonic survival.26 Several investigations indicated that EPF detection was a useful technique to evaluate human infertility and embryonic loss; however, little evidence is available to substantiate the use of EPF detection in commercial swine production. One study indicated that the rosette inhibition test was not quantitative or suitable for pregnancy diagnosis in swine.27
Initially, laparoscopy was adapted in swine for studies of ovarian activity,31 and a research study revealed that pregnancy can be diagnosed with 100% accuracy using this technique.32 Differences in color were noted between gravid and nongravid uteri, because of the greater blood flow to the gravid uterus and increased uterine tone in response to hormonal stimulation. Observation of the corpora lutea allowed an estimation of the number of ova shed, and follicular development in accompaniment with regressing corpora lutea was apparent in animals returning to estrus. When this test was conducted between 16 and 20 days after coitus, pregnancy could be diagnosed before return to estrus in nonconceiving animals. Obviously, laparoscopy is limited to research applications.
Vaginal Biopsy Histologic changes in the vaginal mucosa characterize specific stages of the estrous cycle and pregnancy.33,34 This relationship was the basis for a study in which vaginal biopsies were used to diagnose pregnancy in swine.
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Specimens of vaginal epithelium, obtained with a biopsy instrument, were prepared for histologic examination. Histologic sections of epithelium were categorized according to the number, types, and arrangement of superficial epithelial cells.35 This procedure can be conducted between 18 and 22 days after mating; however, the most reliable results are obtained when the specimen is collected after 25 days of gestation.36 Erroneous test results were obtained for sows and gilts with irregular returns to estrus, sows and gilts affected with cystic ovarian degeneration, immature gilts, anestrous sows, and sows in which resorption of fetuses occurred after pregnancy testing. False negative results were noted when specimens were taken in late pregnancy.36 The vaginal biopsy technique is impractical, and the potential delay in diagnosis with laboratory procedures reduces the usefulness of this technique for routine pregnancy detection.
ULTRASOUND TECHNIQUES Mechanical ultrasound devices commonly are used because they are easy to operate and commercially available and are perceived as being accurate. Three types of ultrasound units are available for pregnancy diagnosis in swine. Each instrument functions on a different scientific principle.
Doppler Ultrasonography Doppler instruments utilize the transmission to and reflection of ultrasound beams from moving objects such as the fetal heart and pulsating umbilical vessels or uterine arteries.37 Blood flow to the uterine artery in the pregnant sow and gilt is detected as a regular 50 to 100 beats per minute, whereas blood flow in the umbilical arteries is detected at 150 to 250 beats per minute.38 Two types of transducer probes—namely, an abdominal and a rectal probe—currently are available for use with the Doppler instruments. The abdominal probe is positioned on the flank of the animal, lateral to the nipples, and aimed at the sow’s pelvis area. The ultrasound waves are emitted and received by transducers and are converted to an audible signal. The rectal probe functions similarly, with the obvious exception of the positioning of the transducer. One study found no differences in sensitivity and specificity between the rectal and the abdominal probes.5 Other reports showed that sensitivity was greater than 85% and specificity was greater than 95%.39,40 Optimal results were obtained when pregnancy determinations were made later than 29 to 34 days; sensitivity decreased with scanning performed earlier in gestation.40 Doppler ultrasound techniques had greater sensitivity, specificity, and overall accuracy than amplitude-depth ultrasonography,40 but substantial variation in the accuracy of different models of amplitude-depth devices may make the results of such comparisons misleading.5,41 After 1 month of gestation, the Doppler devices apparently had greater specificity, whereas the amplitude-depth machines had greater sensitivity.40
The likelihood of false positive results was increased if examinations were done when sows and gilts were in proestrus or estrus, or if sows and gilts had active endometritis.5 False negative results were obtained if examinations were conducted before 30 days, if examinations were conducted in a noisy environment, or if feces became packed around the rectal probe.5,40 Another disadvantage associated with use of Doppler techniques is that training is required in the use of the instrument.
Amplitude-Depth (A-Mode or Pulse Echo) Ultrasonography Amplitude-depth machines utilize ultrasound waves to detect the fluid-filled uterus.42 A transducer is placed against the flank and oriented toward the uterus. Because the contents of the gravid uterus differ in acoustic impedance from that of adjacent tissues, some of the emitted energy is reflected to the transducer and is converted to an audible signal, a deflection on an oscilloscope screen, or illumination of a light (diode) or series of lights.42 In one study, pregnancies were not confirmed before 20 days, but progressive improvement in pregnancy detection was observed from day 20 until day 30.41 From approximately 30 days until 75 days after breeding, the overall accuracy in the determination of pregnancy commonly was greater than 95%.40,43 The percentage of false negative and uncertain determinations increased from 75 days until farrowing.41 These changes in accuracy parallel alterations in volume of allantoic fluids and fetal growth.44 The amplitude-depth instruments had greater sensitivity but less specificity compared with Doppler instruments.40 Some models of amplitude-depth instruments, however, were more severely affected by low sensitivity and specificity.5 Errors in the placement of the transducer resulted in the detection of a fluid-filled urinary bladder, which yielded a falsely positive diagnosis of pregnancy.40 False positive results were obtained when sows were affected with endometrial edema caused by zearalenone toxicosis or pyometra, or when the litter died and was neither aborted nor resorbed.5 False negative results were noted when the test was performed before 28 days of gestation or after day 80.41
Real-Time Ultrasonography Real-time ultrasound scanners have been used to evaluate the reproductive tracts of mares,45 heifers,46 and bitches47 and for pregnancy diagnosis in sows and gilts.48,49 Also, domestic animals such as sheep50,51 and goats52 have been scanned for pregnancy diagnosis and reproductive problems. Real-time ultrasound techniques use beams of sound waves emitted from a multi-transducer. These beams travel in straight lines through different tissues until they encounter boundaries of differing acoustic density. Then they are reflected back to the same transducer and converted to electrical signals, ultimately being displayed on a monitor as a two-dimensional cross section of the interior of the animal.48 The various tissues reflect the sound waves at differing amounts based on their acoustic
Diagnosis of Pregnancy
consuming than use of the abdominal probes; however, the increased structural detail of the ovaries and early pregnancy (days 16 to 20) improves the usefulness of transrectal ultrasonography for use in female pigs. General characteristics of real-time ultrasound probes and representative images are provided in Table 101-2 and Figure 101-1, respectively.
density. Accordingly, tissues such as bone reflect a large portion of the emitted waves and appear white on the screen, whereas other tissues are various shades of gray. Fluid-filled structures such as the urinary bladder or amniotic vesicles are nonechogenic and appear black because they do not reflect any sound waves.50 The combination of these reflections generates the overall image viewed on the screen. Previous work with real-time scanning utilized abdominal probes, with the transducer placed against the flank of the animal. This positioning is lateral to the nipples and posterior to the navel, similar to that for other pregnancy detection devices being used currently.48 From this position the probe is directed toward the back of the animal, allowing the ultrasound waves to pass through the uterus before returning back to the transducer. Amniotic vesicles became visible on real-time scans around 18 or 19 days after breeding; embryos were observed by 21 days and easily detected by 25 to 32 days.53 Fetal movement was observed after day 60.48 Recently, 5.0- and 7.5-mHz probes were used transrectally to determine the pregnancy and estrus status of breeding females.54 Use of the transrectal probes may be marginally more time-
A
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Table 101-2 General Characteristics of Probes for Real-Time Ultrasonography Probe 3.5 mHz 5.0 mHz 7.5 mHz
Depth of Field (cm)
Resolution
Timing*
10–12 7–10 5–7
Low Medium High
Days 25–26 Day 23 Day 21
*Day(s) of gestation on which pregnancy can be diagnosed with reasonable reliability.
B
C Fig. 101-1 Real-time ultrasonographic images of sow uteri observed with a 3.5-mHz sector probe. A, Image from an open sow at day 21 of the estrous cycle. B, A day 21 pregnancy. C, A day 28 pregnancy.
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Early research indicated that real-time ultrasound scanning had greater than 95% sensitivity and specificity at 22 days of gestation or later.48 False negative results were obtained if the scans were performed before day 22 of gestation, when the vesicles were too small to be detected regularly. False positive results were obtained in sows and gilts that had cystic ovarian degeneration or uterine infections resulting in accumulations of fluid. Research with ewes showed that pregnancy status of the animal was a major determinant in the time needed to make a diagnosis using real-time ultrasound scanning. Pregnant ewes were diagnosed in about 10 seconds, whereas scanning of nonpregnant animals took much longer.51 In general, similar time is required for real-time ultrasound scanning for pregnancy diagnosis in female pigs. Our studies demonstrated several sources of variation affecting the success of real-time ultrasound evaluation for pregnancy diagnosis.55 Sources of variation include type of probe, day of gestation when scanning is initiated, and technician skill (Tables 101-3 and 101-4). Parity is a potential source of variation that has not been thoroughly examined. With the exception of the field trials, most controlled studies were conducted with gilts. It is possible that scanning procedures need to be adjusted for the increased abdominal size and the changes in anatomic location and size of the reproductive tract in multiparous sows. Because the initial purchase price ($7000 to $15000) of a real-time ultrasound instrument is considerably higher
Table 101-3 Technician Skill and Success of Real-Time Ultrasonography for Pregnancy Diagnosis in Swine* 3.5-mHz SECTOR PROBE Indicator Sensitivity (%) Specificity (%) Accuracy (%)
5-mHz LINEAR PROBE
Tech A
Tech B
Tech A
Tech B
84.6 95.7 89.9
68 88 78
97.3 91 94.9
91.1 85.4 88.2
*Performed at 21 days after mating.
than that of other pregnancy detection devices, producers and veterinarians often are reluctant to purchase a real-time ultrasound unit. For farms with 100 or 200 sows, this reluctance may be justified. With larger herd sizes, however, the additional costs of a real-time ultrasound instrument quickly diminish on a per sow basis (Table 101-5). Factors affecting the benefits of real-time ultrasonography are interrelated and can have compounding effects on the number of open sow days saved and the money saved per sow. The application of real-time ultrasound scanning as a pregnancy detection technique has greater impact when the farrowing rate is low. The percentage improvement, which is defined as percent of open sows detected by real-time ultrasound evaluation at 23 days that were missed by traditional detection methods (e.g., A-mode, Doppler) at 28 days or sooner, also has dramatic effects on the benefits of real-time ultrasonography. Addi-
Table 101-5 Costs of Real-Time Ultrasonography for Weekly Testing in Swine Breeding Herds of Different Sizes No. of Sows Tested/Week 25 50 100 200 300 400 500 600 700 800
ADDITIONAL COSTS†
Total No. of Sows*
$/Sow Tested
$/Year
500 1,000 2,000 4,000 6,000 8,000 10,000 12,000 14,000 18,000
2.214 1.072 0.501 0.215 0.120 0.073 0.044 0.025 0.012 0.001
2,878 2,787 2,605 2,241 1,877 1,513 1,149 785 421 57
*Hypothetical herd size. † Costs are based on a 3-year life of the real-time ultrasound unit, an initial price of US $7000 for the unit, and adjustments for labor savings (one realtime ultrasound assessment versus two scans with an A-mode instrument). The annual costs of the real-time ultrasound unit include repairs, supplies, and amortization at 8% of the annual percentage rate (APR). Data from Armstrong JD, Almond GW, White S, et al: Accuracy and economics of RTU pregnancy detection, and comparisons with A-mode. North Carolina State University. Available at: http://mark.asci.ncsu.edu/Reproduction/rtu/armstrong.htm (accessed 1997).
Table 101-4 Day of Gestation and Success of Real-Time Ultrasonography for Pregnancy Diagnosis in Swine DAY OF GESTATION* Indicator Sensitivity (%) Specificity (%) Accuracy (%)
17–20
21–23
24–30
38–44
52–58
78.7 50 74.5
100 58.3 97
99.6 70 97.8
100 44.1 98
100 36.4 98.7
*A 5-mHz sector probe was used in this field trial.
Diagnosis of Pregnancy
4
Production Benefits of Real-Time Ultrasound Scanning by Sow Numbers Scanned and Day of Gestation* NPSD/YEAR SAVED BY DAY OF GESTATION Number of Sows 500 1,000 2,000 4,000 6,000 8,000 10,000
23
25
27
570 1,143 2,287 4,576 6,864 9,152 11,440
526 1,055 2,112 4,224 6,337 8,449 10,561
482 967 1,936 3,873 5,809 7,746 9,682
*I.e., number of nonproductive sow days (NPSD)/year saved, as affected by number of sows and day of gestation on which scanning is initiated. Assumptions: 1% improvement above results with A-mode ultrasonography and an 85% farrowing rate. Data from Armstrong JD, Almond GW, White S, et al: Accuracy and economics of RTU pregnancy detection, and comparisons with A-mode. North Carolina State University. Available at: http://mark.asci.ncsu.edu/Reproduction/rtu/armstrong.htm (accessed 1997).
tional savings are gained when producers are willing to institute a 100% culling policy, rather than a standard culling policy (cull after the second return to estrus). Open sows are culled immediately after pregnancy detection with the 100% culling policy. We have observed that many producers become very proficient with the use of real-time ultrasound techniques. These producers can diagnose pregnancy as early as day 23 (sometimes earlier). This proficiency is useful in assessing pregnancy status in breeding groups, when the test day includes animals at days 23 to 28 of gestation. It is not surprising that the greater benefits are gained with the use of real-time ultrasound scanning in large herds or as more sows are tested (Table 101-6). Again, the greatest benefits are gained when early testing is implemented in herds with low farrowing rates. The cost of an open day or nonproductive sow day (NPSD) varies from farm to farm. As the cost of an NPSD increases, the savings per sow with use of real-time ultrasonography also increase (Fig. 101-2). It also is evident that if real-time ultrasound scanning detects a greater percentage of open sows than is found with the traditional methods, then additional savings per sow will result. Real-time ultrasound scanning appears to be more versatile than the other methods of pregnancy diagnosis currently available. Besides pregnancy detection, it has been used to assess reproductive disorders in goats52 and to evaluate carcass characteristics in growing pigs.56 These findings lend further support to the potential for other uses for this technique in swine production. For instance, pseudopregnant sows and gilts with uteri containing mummified fetuses have been differentiated from pregnant sows.57 Recently, it was demonstrated that real-time ultrasound scanning is an effective technique to identify pseudopregnant sows between days 65 and 75 after
Dollar per sow
Table 101-6
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$2.00/NPSD $1.50/NPSD $1.00/NPSD $.50/NPSD
3 2 1 0 1
2 3 4 Percent improvement
5
Fig. 101-2 Money saved per sow is influenced by both the percentage improvement and the cost of a nonproductive sow day (NPSD). The real-time ultrasound scanner was used at 23 days after mating, and the data are based on scanning 200 sows per week, with a 75% farrowing rate. The percentage improvement is based on a comparison of real-time ultrasound scanning at 23 days with amplitude-depth scanning at 28 and 35 days of gestation.
mating.58 Although the uterus of a pseudopregnant sow may contain fluid, the failure to observe fetal skeletons is indicative of pseudopregnancy. Furthermore, past research showed that this technique was useful to identify and distinguish sows and gilts with endometritis from females in later stages of pregnancy.57
SUMMARY AND CONCLUSIONS The advantages of sensitive and specific methods for early pregnancy diagnosis in swine include early detection of conception failure, forecasting production levels, and early identification of nonpregnant animals, which facilitates decisions regarding culling, treatment, or rebreeding. At present, detection of nonconceiving sows that return to estrus and use of amplitude-depth ultrasonography are the most widely used methods of pregnancy diagnosis. Despite routine use of these traditional methods, a common finding is that many sows either fail to farrow after being considered pregnant or return to estrus at irregular times during a presumed pregnancy. Perhaps the most promising technique for porcine pregnancy detection is real-time ultrasound scanning. This method is used routinely in a variety of species; however, applied research and improved technology have enhanced its applications in commercial sow farms. Perhaps the most intriguing aspect of real-time ultrasound scanning is that the user can visualize the uterus and its contents. Despite the obvious need for improved pregnancy diagnosis abilities for swine producers, little progress or changes were made until the development and application of real-time ultrasound techniques.
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2. Signoret JP: Reproductive behavior of pigs. J Reprod Fertil Suppl 1970;11:105–117. 3. Jochle W, Schilling E: Improvement of conception rate and diagnosis of pregnancy in sows by an androgen-oestrogendepot preparation. J Reprod Fertil 1965;10:439–440. 4. Bosc MJ, Martinat-Botte F, Nicolle A: Etude de deux technique de diagnostic de gestation chez la truie. Ann Zootech 1975;24:651–660. 5. Almond GW, Dial GD: Pregnancy diagnosis in swine: a comparison of the accuracies of mechanical and endocrine tests with return to estrus. J Am Vet Med Assoc 1986;189:1567– 1571. 6. Moeljono MPE, Thatcher WW, Bazer FW: A study of prostaglandin F2 as the luteolysin in swine: II. Characterization and comparison of prostaglandin-F2, estrogens and progestin concentrations in utero-ovarian vein plasma of nonpregnant and pregnant gilts. Prostaglandins 1977;14: 543–555. 7. Bazer FW, Thatcher WW: Theory of maternal recognition of pregnancy in swine based upon oestrogen controlled endocrine versus exocrine secretions of prostaglandin-F2α by uterine endometrium. Prostaglandins 1977;14:397–401. 8. Bosc MJ, Martinat-Botte F, Terqui M: Practical uses of prostaglandins in pigs. Acta Vet Scand Suppl 1981;77: 209–226. 9. Perry JS, Heap RB, Burton RD, et al: Endocrinology of the blastocyst and its role in the establishment of pregnancy. J Reprod Fertil 1976;25(Suppl):85–104. 10. Ellendorff F, Meyer JN, Elsaesser F: Prospects and problems and fertility diagnosis in the pig by aid of progesterone determination. Br Vet J 1976;132:543–550. 11. Andersson AM, Einarsson S: Studies on the oestrus and ovarian activity during five successive oestrous cycles in gilts. Acta Vet Scand 1980;21:677–688. 12. Larsson K, Edqvist LE, Einarsson S, et al: Determination of progesterone in peripheral blood-plasma as a diagnostic aid in female swine. Nord Vet Med 1975;27:167–172. 13. Ellicott AR, Dziuk PJ: Minimum daily dose of progesterone and plasma concentration for maintenance of pregnancy in ovariectomized gilts. Biol Reprod 1973;9:300–304. 14. Sanders H, Rajamahendren R, Burton B: The development of a simple fecal immunoreactive progestin assay to monitor reproductive function in swine. Can Vet J 1994;35:355–358. 15. Hay Ma, King WA, Gartley CJ, et al: Correlation of periovulatory serum and fecal progestins in the domestic dog. Can J Vet Res 2000;64:59–63. 16. Hirata S, Mori Y: Monitoring reproductive status by fecal progesterone analysis in ruminants. J Vet Med Sci 1995;57: 845–850. 17. Robertson HA, Dwyer RJ, King GJ: Oestrogens in fetal and maternal fluids throughout pregnancy in the pig and comparisons with the ewe and cow. J Endocrinol 1985; 106:355–360. 18. Guthrie HD, Deaver DR: Estrone concentration in the peripheral plasma of pregnant and nonpregnant gilts. Theriogenology 1979;11:321–329. 19. Cunningham NF: Pregnancy diagnosis in sows based on serum oestrone sulphate concentration. Br Vet J 1982;138: 543–544. 20. Seren E, Mattioli M, Gaiani R, et al: Direct estimation of urine estrone conjugate for a rapid pregnancy diagnosis in sows. Theriogenology 1983;19:817–822. 21. Robertson HA, King GJ, Dyck GW: The appearance of oestrone sulphate in the peripheral plasma of the pig early in pregnancy. J Reprod Fertil 1978;52:337–338. 22. Cunningham NF, Hattersley JP, Wrathall AE: Pregnancy diagnosis in sows based on serum oestrone sulphate concentration. Vet Rec 1983;113:229–233.
23. Kensinger RS, Collier RJ, Bazer FW, et al: Effect of number of conceptuses on maternal hormone concentrations in the pig. J Anim Sci 1986;62:1666–1674. 24. Clarke FM, Morton H, Clunie CJA: Detection and separation of two serum factors responsible for depression of lymphocyte activity in pregnancy. Clin Exp Immunol 1978;32:318– 323. 25. Koch E, Ellendorff F: Prospects and limitations of the rosette inhibition test to detect activity of early pregnancy factor in the pig. J Reprod Fertil 1985;74:29–38. 26. Koch E, Morton H, Ellendorf F: Early pregnancy factor: biology and practical application. Br Vet J 1983;139:52–58. 27. Greco CR, Vivas AB, Bosch RA: Evaluation of the method for early pregnancy factor detection (EPF) in swine: significance in early pregnancy diagnosis. Acta Physiol Pharmacol Ther Latinoam 1992;42:43–50. 28. Rapic S: Radiological diagnosis of pregnancy in swine. Vet Rec 1961;21:171. 29. Wrathall AE, Bailey J, Hebert CN: A radiographic study of development of the appendicular skeleton in the fetal pig. Res Vet Sci 1974;17:154–168. 30. Cameron RDA: Pregnancy diagnosis in the sow by rectal examination. Aust Vet J 1977;53:432–435. 31. Wildt DE, Fujimoto S, Spencer JL, et al: Direct ovarian observation in the pig by means of laparoscopy. J Reprod Fertil 1973;35:541–543. 32. Wildt DE, Morcom CB, Dukelow WR: Laparoscopic pregnancy diagnosis and uterine fluid recovery in swine. J Reprod Fertil 1975;44:301–304. 33. Morton DB, Rankin JEF: The histology of the vaginal epithelium of the sow in oestrus and its use in pregnancy diagnosis. Vet Rec 1969;84:658–666. 34. Walker D: Pregnancy diagnosis in pigs. Vet Rec 1972;90: 139–144. 35. Williamson P, Hennessy D: An assessment of the vaginal biopsy technique of pregnancy diagnosis in sows. Aust Vet J 1975;51:91–93. 36. Done JT, Heard TW: Early pregnancy diagnosis in the sow by vaginal biopsy. Vet Rec 1968;82:64–68. 37. Fraser AF, Nagaratnam V, Callicott RB: The comprehensive use of Doppler ultrasound in farm animal reproduction. Vet Rec 1971;88:202–205. 38. Swensson T: Foetus sound detection for control of pregnancy in swine. Svensk Veterin 1978;30:781–783. 39. McCaughey WJ, Rea CC: Pregnancy diagnosis in sows: a comparison of the vaginal biopsy and Doppler ultrasound techniques. Vet Rec 1979;104:255–258. 40. Almond GW, Bosu WTK, King GJ: Pregnancy diagnosis in swine: a comparison of two ultrasound instruments. Can Vet J 1985;26:205–208. 41. Holtz W: Pregnancy detection in swine by pulse mode ultrasound. Anim Reprod Sci 1982;4:219–226. 42. Lindahl IL, Totsch JP, Martin PA, et al: Early diagnosis of pregnancy in sows by ultrasonic amplitude-depth analysis. J Anim Sci 1975;40:220–222. 43. Hansen LH, Christensen IJ: The accuracy of porcine pregnancy diagnosis by a newly developed ultrasonic A-scan tester. Br Vet J 1976;132:66–67. 44. Knight JW, Bazer FW, Thatcher WW, et al: Conceptus development in intact and unilaterally hysterectomizedovariectomized gilts: interrelationships among hormonal status, placental development, fetal fluids and fetal growth. J Anim Sci 1977;44:620–637. 45. Torbeck RL, Rautanen NW: Early pregnancy diagnosis in the mare with ultrasonography. J Equine Vet Sci 1982;2:204–207. 46. Pierson RA, Ginther OJ: Ultrasonography for detection of pregnancy and study of embryonic development in heifers. Theriogenology 1984;22:225–233.
Infertility Associated with Abnormalities of the Estrous Cycle and the Ovaries 47. Bondestam S, Alitalo I, Karkkainen M: Realtime ultrasound pregnancy diagnosis in the bitch. J Small Anim Pract 1983;24:145–151. 48. Inaba T, Nakazima Y, Matsui N, et al: Early pregnancy diagnosis in sows by ultrasonic linear electronic scanning. Theriogenology 1983;20:97–101. 49. Jackson GH: Pregnancy diagnosis in the sow using real-time ultrasonic scanning. Vet Rec 1986;119:90–91. 50. Buckrell BC, Bonnett BN, Johnson WH: The use of real-time ultrasound rectally for early pregnancy diagnosis in sheep. Theriogenology 1986;25:665–673. 51. Davey CG: An evaluation of pregnancy testing in sheep using a real-time ultrasound scanner. Aust Vet J 1986;63:347– 349. 52. Pieterse MC, Taverne MAM: Hydrometra in goats: diagnosis with real-time ultrasound and treatment with prostaglandins or oxytocin. Theriogenology 1986;26:813–821. 53. Botero O, Martinat-Botte F, Chevalier F: Ultrasonic echography for early pregnancy diagnosis in the sow. Proceedings of the 8th International Pig Veterinary Society Congress, Ghent, Belgium, 1984, p 306.
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54. Knox RV, Althouse GC: Visualizing the reproductive tract of the female pig using real-time ultrasonography. Swine Health Prod 1999;7:207–215. 55. Armstrong JD, Almond GW, White S, et al: Accuracy and economics of RTU pregnancy detection, and comparisons with A-mode. North Carolina State University. Available at: http://mark.asci.ncsu.edu/Reproduction/rtu/armstrong.htm (accessed 1997). 56. McLaren DG, McKeith FM, Novakofski J: Prediction of carcass characteristics at market weight from serial real-time ultrasound measures of backfat and loin eye area in growing pigs. J Anim Sci 1989;67:1657–1667. 57. Martinat-Botte F, Lepercq M, Forgerit Y, et al: Evaluation of swine embryonic growth by ultrasonography. Proceedings of the 9th International Pig Veterinary Society Congress, Barcelona, Spain, 1986, p 27. 58. Flowers WL: Real-time ultrasonography and diagnosis of pseudopregnancy in swine. North Carolina State University. Available at: http://mark.asci.ncsu.edu/Reproduction/rtu/ reprortu.htm (accessed 2001).
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Infertility Associated with Abnormalities of the Estrous Cycle and the Ovaries GLEN W. ALMOND
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arious reports have demonstrated the role of infectious agents in porcine reproductive failure. For most infectious agents, researchers and veterinary practitioners have elucidated the pathogenesis, modes of transmission, and reasonably effective control programs. By contrast, porcine reproductive and respiratory syndrome virus (PRRSV) disease continues to be difficult to control, and the swine industry recognizes the economic impact of the virus on all phases of production. PRRSV disease continues to be detrimental to reproductive performance in sow herds, with variable severity of clinical signs in affected animals. With these widespread problems associated with PRRSV, pig producers often attribute reproductive failure to the virus when in fact the underlying causes are noninfectious. Unfortunately, the precise pathogenic mechanisms of noninfectious causes of repro-
ductive failure also are elusive, and the interactions between the various factors affecting reproduction create major challenges to any efforts to improve the performance of the breeding herd. Various investigators have examined the physiologic control of estrus, ovulation, conception, and pregnancy; however, the endocrine changes associated with these processes are more complex than was previously believed. Season, nutrition, environment, and management are well recognized for their potential to alter reproductive processes. In addition, recent studies revealed that various components of the immune system also possess profound roles in porcine reproduction. This chapter provides information regarding the physiologic mechanisms and “management” factors involved with infertility due to abnormalities of the porcine estrous cycle.
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Diagnosis of Pregnancy GLEN W. ALMOND
E
arly and accurate identification of pregnant and nonpregnant sows and gilts has a strong potential to increase reproductive efficiency of commercial swine farms. Detection of returns to estrus after mating, ultrasound techniques, and several other methods have been used for pregnancy diagnosis1; however, for various reasons, only three or four techniques currently are used in commercial farms. An ideal pregnancy detection technique is not available, and most producers use either a combination of techniques or one technique that apparently fulfills their requirements. Some methods are restricted to research applications, and it is unlikely that these methods will be adapted for on-farm use. This chapter reviews the techniques for pregnancy diagnosis in swine; the practical applications, or lack thereof, are emphasized for each technique (Table 101-1). For most procedures, sensitivity (ability to detect pregnant animals, representing the proportion of pregnant animals that test positively) and specificity (ability to detect nonpregnant animals, representing the proportion of nonpregnant animals that test negatively) are used to assess accuracy.
• Submissive sows are housed in groups with dominant sows. • Group sizes are too large to permit individual assessments of estrus. • Sows are housed in stalls that do not permit the sow to detect the presence of the boar. • The design of gestation facilities does not allow daily boar exposure to the bred sow. • Breeding herd personnel fail to dedicate sufficient time to estrus detection. • Breeding herd personnel lack adequate training to identify sows in estrus.
HORMONE CONCENTRATIONS Serum concentrations of prostaglandin F2α (PGF2α), progesterone, and estrone sulfate were used as indicators of pregnancy. These hormone concentrations are dynamic, and considerable knowledge regarding endocrine changes in pregnant and nonpregnant sows is required for correct use of these techniques for pregnancy diagnosis. Owing to technical requirements, these methods are not used in the swine industry.
DETECTION OF ESTRUS
Prostaglandin F2a
A common pregnancy detection technique is observation of the sow for failure to return to estrus after mating. This technique is based on the premise that nonpregnant sows will return to estrus within 17 to 24 days after breeding. Detection of estrus is improved if the sow’s behavior is observed in the presence of a boar.2 Thus, this technique requires gestation facilities that are designed to allow daily fenceline contact between boars and sows, or the placement of the boar and sow in the same pen each day. Injections of estradiol or estradiol plus testosterone will enhance estrous behavior in sows that are not pregnant3; however, these steroids are not approved for use in swine in the United States. An early study reported an accuracy of 39% for the detection of return to estrus between 19 and 25 days after mating.4 By contrast, daily estrus detection throughout gestation enabled a 98% accuracy in predicting farrowing rate.5 Albeit rarely seen, a false negative result can be obtained if a pregnant sow shows spontaneous estrus.5 False positive results occur in the following scenarios:
The endometrium of the nongravid uterus secretes PGF2α into the uterine vein between days 12 and 15 of the cycle, thereby inducing regression of the corpora lutea.6 When viable embryos are present, PGF2α is not secreted into the uterine vein.7 The prostaglandin pregnancy test is based on the principle that if serum concentrations of PGF2α are low (less than 200 pg/ml) or undetectable between days 13 and 15 after mating, the sow can be assumed to be pregnant.8 Routine blood sample collection, without the use of indomethacin or other cyclo-oxygenase inhibitors, causes release of PGF2α from blood constituents. This PGF2α release leads to obvious problems with interpretation of serum PGF2α concentrations; however, prostaglandin metabolites are more stable, and serum metabolite concentrations are reasonable indicators of prostaglandin concentrations. The prostaglandin pregnancy test has approximately 90% sensitivity and 70% specificity. Accuracy is lower when animals have delayed returns to estrus, or when fetal death occurs and sows manifest pseudopregnancy. This diagnostic method can be used during early pregnancy, but its unreliability in the detection of nonpregnant animals and the necessity of extensive laboratory procedures limit its practical application.
• Sows become persistently anestrous as a result of cystic ovarian degeneration or inactive, acyclic ovaries, or become pseudopregnant.
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Table 101-1 Applications of Techniques Available for Pregnancy Diagnosis in Swine TIME OF TEST DURING PREGNANCY*
APPLICATION Technique Early pregnancy factor Estrus detection Estrogen injections Laparoscopy Prostaglandin F2α Progesterone Estrone sulfate Rectal palpation Vaginal biopsy Doppler ultrasonography Amplitude-depth ultrasonography Real-time ultrasonography
Commercial
Diagnostic
Research
Ultra-early
X
X
X
X
X X X
X X X X X X X
Late
X X X
X X X X X
Early
X X X X
X
X
X
X
X X X
*Ultra-early: before 18 days after breeding; early: 18 to 24 days after breeding; late: beyond 24 days after breeding.
Progesterone Maintenance of the corpus luteum (CL) is the result of a blastocyst “signal” that is produced at 10 to 12 days after mating.9 The blastocyst-induced maintenance of corpora lutea causes serum progesterone concentrations to remain high (greater than 5 ng/ml) throughout pregnancy. Thus, serum concentrations of progesterone are high in pregnant sows and gilts during the expected time of return to estrus and low (less than 5 ng/ml) in bred sows and gilts that fail to conceive.10 The interestrus interval for sows of various parities ranges from 17 to 24 days, with a mean of 20 to 21 days and a mode of 20 days.11 Therefore, the optimal time to obtain blood samples for progesterone determinations is from 17 to 20 days if nonconceiving sows and gilts are to be identified before the time they return to estrus. The serum concentration of progesterone that most accurately discriminates the nonpregnant from the pregnant sow or gilt has not been determined. Concentrations of 4, 5, 7, 7.5, and 9 ng of progesterone/ml of serum were used to discern pregnancy status5,10; a concentration of 5 ng/ml is most commonly used. The progesterone pregnancy test has greater than 97% sensitivity at 17 to 24 days, but specificity ranges from 60% to 90%.5,12 False positive results are common when nonconceiving sows and gilts have delayed or irregular returns to estrus, and when nonpregnant sows and gilts are anestrous as a result of cystic ovarian disease.5 False negative results may be the result of laboratory error because it is assumed that greater than 4 ng of progesterone/ml of serum is required for pregnancy maintenance in swine.13 Commercial enzyme-linked immunosorbent assays (ELISAs) to measure blood concentrations of progesterone in swine can be used on farms or in veterinary clinics,
thereby reducing the need for laboratory-based radioimmunoassays. The necessity of collecting blood is a significant limitation of this method; however, methods to quantitate fecal progestins were evaluated for monitoring reproductive function in swine,14 dogs,15 and ruminants.16 It was evident that the extraction and assay procedures are feasible alternatives to blood progesterone assays. Despite the potential use of fecal progestin determinations, direct applications of this methodology for pregnancy diagnosis have not gained popularity, nor have they been evaluated on a large scale in commercial pig production.
Estrone Sulfate A high proportion of fetal estrogens is secreted from the uterus into the maternal circulation as estrone sulfate.17 Estrone sulfate initially appears in the maternal circulation at approximately 16 to 20 days and rises linearly to peak levels between 25 and 30 days before decreasing to a nadir at 35 to 45 days.18 A second increase in estrone sulfate occurs concomitantly with increases in other estrogens, commencing at 70 to 80 days and continuing until farrowing. Urinary and serum estrone sulfate concentrations have been investigated for applicability as pregnancy tests.5,19,20 A 10-fold to 100-fold increase in maternal estrone sulfate concentrations typically occurs between 25 and 30 days after coitus in sows that conceive.21 Because estrone sulfate increases during early and late pregnancy, determination of estrone sulfate levels has potential applications as an early pregnancy diagnosis test and as a confirmatory test later during pregnancy. Parity, season, and day of pregnancy when blood was collected have some effect on estrone sulfate concentrations.
Diagnosis of Pregnancy Serum estrone sulfate concentrations greater than 0.5 ng/ml are indicative of pregnancy, whereas concentrations less than 0.5 ng/ml are suggestive of nonpregnant status.5,19 The estrone sulfate pregnancy test has greater than 97% sensitivity and greater than 88% specificity when serum samples are collected between 25 and 30 days of pregnancy.5 False positive results may be attributable to a transient increase of estrone sulfate concentrations in some sows and gilts during proestrus.18 False negative results were obtained in sows or gilts with a premature or delayed rise in estrone sulfate concentrations22 or in sows and gilts that had less than 4 pigs in a litter.5 As with other early tests of pregnancy, animals may be correctly diagnosed as pregnant but subsequently will fail to farrow if the fetuses die after the test has been conducted. Pseudopregnant sows frequently retain the endocrine function of the corpora lutea for prolonged periods and may appear to be pregnant even though they no longer have viable fetuses. Other sows experience loss of their pregnancies, followed by development of acyclic, anovulatory ovaries or cystic ovaries, and similarly fail to show estrus for various time periods. Serum concentrations of estrone sulfate in pseudopregnant animals were similar to those in females that had not been mated and distinctly less than those in pregnant sows.23 Urinary concentrations of estrone conjugates also have been used to predict pregnancy and to diagnose fertility problems.20 for these investigations, urine samples were obtained through the use of vaginal sponges. It should be noted that the glucuronide conjugate of estrone, rather than the sulfate form, was measured; thus, different quantitative procedures were required. Quantitative commercial assay kits for the determination of estrone sulfate concentrations in serum from swine are not available. The need to collect blood (or urine) samples limits the practical application of this technique for pregnancy diagnosis in swine.
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PHYSICAL METHODS Radiography Radiography is a seldom-used method for pregnancy diagnosis in swine. In research studies, it was used after the sixth week of pregnancy,28 when the fetal skeleton begins to calcify. Fetal age, viability, and abnormalities were determined with radiography.29 Equipment costs, potential health hazards to users, and the impracticality of radiography in production facilities render this technique unsuitable for pregnancy diagnosis in commercial swine.
Rectal Palpation Pregnancy diagnosis by rectal palpation of the sow has been demonstrated to be practical and highly accurate.30 Sows in the relevant study were examined while standing in gestation crates or pens, or while tethered. The technique involves examination of the cervix and uterus, together with palpation of the middle uterine artery to assess its size, degree of tone, and type of pulse. Before 21 days of gestation, rectal palpation had a 30% sensitivity, but the sensitivity increased to 75%, 94%, and 100% in animals at 21 to 27, 28 to 30, and 60 days to term, respectively.30 The pelvic canal and rectum often were too small for the procedure to be used on low-parity sows. False positive results were obtained if the external iliac artery or one of its branches was mistakenly identified as the middle uterine artery. False negative results, presumably due to errors in palpation technique or performance of palpation too early, were more common than false positive diagnoses. Despite the potential application of this technique, it has not gained popularity in North America.
Laparoscopy Early Pregnancy Factor Early pregnancy factor (EPF) activity is dependent on the presence of two components: EPF-A and EPF-B. Factor A is formed in the uterus during estrus and pregnancy, whereas EPF-B is produced in the ovary and is associated only with pregnancy. The production of EPF-B is a result of a combined action of endocrine signals from the pituitary and the zygote.24 Serum concentrations of EPF peak 24 to 48 hours after fertilization and exhibit a polyphasic pattern throughout gestation.25 Detection of EPF, based on a rosette inhibition test, is time-consuming and cumbersome and possesses other limitations. Various applications of EPF detection have been proposed for embryo transfer programs and assessment of infertility and early embryonic survival.26 Several investigations indicated that EPF detection was a useful technique to evaluate human infertility and embryonic loss; however, little evidence is available to substantiate the use of EPF detection in commercial swine production. One study indicated that the rosette inhibition test was not quantitative or suitable for pregnancy diagnosis in swine.27
Initially, laparoscopy was adapted in swine for studies of ovarian activity,31 and a research study revealed that pregnancy can be diagnosed with 100% accuracy using this technique.32 Differences in color were noted between gravid and nongravid uteri, because of the greater blood flow to the gravid uterus and increased uterine tone in response to hormonal stimulation. Observation of the corpora lutea allowed an estimation of the number of ova shed, and follicular development in accompaniment with regressing corpora lutea was apparent in animals returning to estrus. When this test was conducted between 16 and 20 days after coitus, pregnancy could be diagnosed before return to estrus in nonconceiving animals. Obviously, laparoscopy is limited to research applications.
Vaginal Biopsy Histologic changes in the vaginal mucosa characterize specific stages of the estrous cycle and pregnancy.33,34 This relationship was the basis for a study in which vaginal biopsies were used to diagnose pregnancy in swine.
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Specimens of vaginal epithelium, obtained with a biopsy instrument, were prepared for histologic examination. Histologic sections of epithelium were categorized according to the number, types, and arrangement of superficial epithelial cells.35 This procedure can be conducted between 18 and 22 days after mating; however, the most reliable results are obtained when the specimen is collected after 25 days of gestation.36 Erroneous test results were obtained for sows and gilts with irregular returns to estrus, sows and gilts affected with cystic ovarian degeneration, immature gilts, anestrous sows, and sows in which resorption of fetuses occurred after pregnancy testing. False negative results were noted when specimens were taken in late pregnancy.36 The vaginal biopsy technique is impractical, and the potential delay in diagnosis with laboratory procedures reduces the usefulness of this technique for routine pregnancy detection.
ULTRASOUND TECHNIQUES Mechanical ultrasound devices commonly are used because they are easy to operate and commercially available and are perceived as being accurate. Three types of ultrasound units are available for pregnancy diagnosis in swine. Each instrument functions on a different scientific principle.
Doppler Ultrasonography Doppler instruments utilize the transmission to and reflection of ultrasound beams from moving objects such as the fetal heart and pulsating umbilical vessels or uterine arteries.37 Blood flow to the uterine artery in the pregnant sow and gilt is detected as a regular 50 to 100 beats per minute, whereas blood flow in the umbilical arteries is detected at 150 to 250 beats per minute.38 Two types of transducer probes—namely, an abdominal and a rectal probe—currently are available for use with the Doppler instruments. The abdominal probe is positioned on the flank of the animal, lateral to the nipples, and aimed at the sow’s pelvis area. The ultrasound waves are emitted and received by transducers and are converted to an audible signal. The rectal probe functions similarly, with the obvious exception of the positioning of the transducer. One study found no differences in sensitivity and specificity between the rectal and the abdominal probes.5 Other reports showed that sensitivity was greater than 85% and specificity was greater than 95%.39,40 Optimal results were obtained when pregnancy determinations were made later than 29 to 34 days; sensitivity decreased with scanning performed earlier in gestation.40 Doppler ultrasound techniques had greater sensitivity, specificity, and overall accuracy than amplitude-depth ultrasonography,40 but substantial variation in the accuracy of different models of amplitude-depth devices may make the results of such comparisons misleading.5,41 After 1 month of gestation, the Doppler devices apparently had greater specificity, whereas the amplitude-depth machines had greater sensitivity.40
The likelihood of false positive results was increased if examinations were done when sows and gilts were in proestrus or estrus, or if sows and gilts had active endometritis.5 False negative results were obtained if examinations were conducted before 30 days, if examinations were conducted in a noisy environment, or if feces became packed around the rectal probe.5,40 Another disadvantage associated with use of Doppler techniques is that training is required in the use of the instrument.
Amplitude-Depth (A-Mode or Pulse Echo) Ultrasonography Amplitude-depth machines utilize ultrasound waves to detect the fluid-filled uterus.42 A transducer is placed against the flank and oriented toward the uterus. Because the contents of the gravid uterus differ in acoustic impedance from that of adjacent tissues, some of the emitted energy is reflected to the transducer and is converted to an audible signal, a deflection on an oscilloscope screen, or illumination of a light (diode) or series of lights.42 In one study, pregnancies were not confirmed before 20 days, but progressive improvement in pregnancy detection was observed from day 20 until day 30.41 From approximately 30 days until 75 days after breeding, the overall accuracy in the determination of pregnancy commonly was greater than 95%.40,43 The percentage of false negative and uncertain determinations increased from 75 days until farrowing.41 These changes in accuracy parallel alterations in volume of allantoic fluids and fetal growth.44 The amplitude-depth instruments had greater sensitivity but less specificity compared with Doppler instruments.40 Some models of amplitude-depth instruments, however, were more severely affected by low sensitivity and specificity.5 Errors in the placement of the transducer resulted in the detection of a fluid-filled urinary bladder, which yielded a falsely positive diagnosis of pregnancy.40 False positive results were obtained when sows were affected with endometrial edema caused by zearalenone toxicosis or pyometra, or when the litter died and was neither aborted nor resorbed.5 False negative results were noted when the test was performed before 28 days of gestation or after day 80.41
Real-Time Ultrasonography Real-time ultrasound scanners have been used to evaluate the reproductive tracts of mares,45 heifers,46 and bitches47 and for pregnancy diagnosis in sows and gilts.48,49 Also, domestic animals such as sheep50,51 and goats52 have been scanned for pregnancy diagnosis and reproductive problems. Real-time ultrasound techniques use beams of sound waves emitted from a multi-transducer. These beams travel in straight lines through different tissues until they encounter boundaries of differing acoustic density. Then they are reflected back to the same transducer and converted to electrical signals, ultimately being displayed on a monitor as a two-dimensional cross section of the interior of the animal.48 The various tissues reflect the sound waves at differing amounts based on their acoustic
Diagnosis of Pregnancy
consuming than use of the abdominal probes; however, the increased structural detail of the ovaries and early pregnancy (days 16 to 20) improves the usefulness of transrectal ultrasonography for use in female pigs. General characteristics of real-time ultrasound probes and representative images are provided in Table 101-2 and Figure 101-1, respectively.
density. Accordingly, tissues such as bone reflect a large portion of the emitted waves and appear white on the screen, whereas other tissues are various shades of gray. Fluid-filled structures such as the urinary bladder or amniotic vesicles are nonechogenic and appear black because they do not reflect any sound waves.50 The combination of these reflections generates the overall image viewed on the screen. Previous work with real-time scanning utilized abdominal probes, with the transducer placed against the flank of the animal. This positioning is lateral to the nipples and posterior to the navel, similar to that for other pregnancy detection devices being used currently.48 From this position the probe is directed toward the back of the animal, allowing the ultrasound waves to pass through the uterus before returning back to the transducer. Amniotic vesicles became visible on real-time scans around 18 or 19 days after breeding; embryos were observed by 21 days and easily detected by 25 to 32 days.53 Fetal movement was observed after day 60.48 Recently, 5.0- and 7.5-mHz probes were used transrectally to determine the pregnancy and estrus status of breeding females.54 Use of the transrectal probes may be marginally more time-
A
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Table 101-2 General Characteristics of Probes for Real-Time Ultrasonography Probe 3.5 mHz 5.0 mHz 7.5 mHz
Depth of Field (cm)
Resolution
Timing*
10–12 7–10 5–7
Low Medium High
Days 25–26 Day 23 Day 21
*Day(s) of gestation on which pregnancy can be diagnosed with reasonable reliability.
B
C Fig. 101-1 Real-time ultrasonographic images of sow uteri observed with a 3.5-mHz sector probe. A, Image from an open sow at day 21 of the estrous cycle. B, A day 21 pregnancy. C, A day 28 pregnancy.
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Early research indicated that real-time ultrasound scanning had greater than 95% sensitivity and specificity at 22 days of gestation or later.48 False negative results were obtained if the scans were performed before day 22 of gestation, when the vesicles were too small to be detected regularly. False positive results were obtained in sows and gilts that had cystic ovarian degeneration or uterine infections resulting in accumulations of fluid. Research with ewes showed that pregnancy status of the animal was a major determinant in the time needed to make a diagnosis using real-time ultrasound scanning. Pregnant ewes were diagnosed in about 10 seconds, whereas scanning of nonpregnant animals took much longer.51 In general, similar time is required for real-time ultrasound scanning for pregnancy diagnosis in female pigs. Our studies demonstrated several sources of variation affecting the success of real-time ultrasound evaluation for pregnancy diagnosis.55 Sources of variation include type of probe, day of gestation when scanning is initiated, and technician skill (Tables 101-3 and 101-4). Parity is a potential source of variation that has not been thoroughly examined. With the exception of the field trials, most controlled studies were conducted with gilts. It is possible that scanning procedures need to be adjusted for the increased abdominal size and the changes in anatomic location and size of the reproductive tract in multiparous sows. Because the initial purchase price ($7000 to $15000) of a real-time ultrasound instrument is considerably higher
Table 101-3 Technician Skill and Success of Real-Time Ultrasonography for Pregnancy Diagnosis in Swine* 3.5-mHz SECTOR PROBE Indicator Sensitivity (%) Specificity (%) Accuracy (%)
5-mHz LINEAR PROBE
Tech A
Tech B
Tech A
Tech B
84.6 95.7 89.9
68 88 78
97.3 91 94.9
91.1 85.4 88.2
*Performed at 21 days after mating.
than that of other pregnancy detection devices, producers and veterinarians often are reluctant to purchase a real-time ultrasound unit. For farms with 100 or 200 sows, this reluctance may be justified. With larger herd sizes, however, the additional costs of a real-time ultrasound instrument quickly diminish on a per sow basis (Table 101-5). Factors affecting the benefits of real-time ultrasonography are interrelated and can have compounding effects on the number of open sow days saved and the money saved per sow. The application of real-time ultrasound scanning as a pregnancy detection technique has greater impact when the farrowing rate is low. The percentage improvement, which is defined as percent of open sows detected by real-time ultrasound evaluation at 23 days that were missed by traditional detection methods (e.g., A-mode, Doppler) at 28 days or sooner, also has dramatic effects on the benefits of real-time ultrasonography. Addi-
Table 101-5 Costs of Real-Time Ultrasonography for Weekly Testing in Swine Breeding Herds of Different Sizes No. of Sows Tested/Week 25 50 100 200 300 400 500 600 700 800
ADDITIONAL COSTS†
Total No. of Sows*
$/Sow Tested
$/Year
500 1,000 2,000 4,000 6,000 8,000 10,000 12,000 14,000 18,000
2.214 1.072 0.501 0.215 0.120 0.073 0.044 0.025 0.012 0.001
2,878 2,787 2,605 2,241 1,877 1,513 1,149 785 421 57
*Hypothetical herd size. † Costs are based on a 3-year life of the real-time ultrasound unit, an initial price of US $7000 for the unit, and adjustments for labor savings (one realtime ultrasound assessment versus two scans with an A-mode instrument). The annual costs of the real-time ultrasound unit include repairs, supplies, and amortization at 8% of the annual percentage rate (APR). Data from Armstrong JD, Almond GW, White S, et al: Accuracy and economics of RTU pregnancy detection, and comparisons with A-mode. North Carolina State University. Available at: http://mark.asci.ncsu.edu/Reproduction/rtu/armstrong.htm (accessed 1997).
Table 101-4 Day of Gestation and Success of Real-Time Ultrasonography for Pregnancy Diagnosis in Swine DAY OF GESTATION* Indicator Sensitivity (%) Specificity (%) Accuracy (%)
17–20
21–23
24–30
38–44
52–58
78.7 50 74.5
100 58.3 97
99.6 70 97.8
100 44.1 98
100 36.4 98.7
*A 5-mHz sector probe was used in this field trial.
Diagnosis of Pregnancy
4
Production Benefits of Real-Time Ultrasound Scanning by Sow Numbers Scanned and Day of Gestation* NPSD/YEAR SAVED BY DAY OF GESTATION Number of Sows 500 1,000 2,000 4,000 6,000 8,000 10,000
23
25
27
570 1,143 2,287 4,576 6,864 9,152 11,440
526 1,055 2,112 4,224 6,337 8,449 10,561
482 967 1,936 3,873 5,809 7,746 9,682
*I.e., number of nonproductive sow days (NPSD)/year saved, as affected by number of sows and day of gestation on which scanning is initiated. Assumptions: 1% improvement above results with A-mode ultrasonography and an 85% farrowing rate. Data from Armstrong JD, Almond GW, White S, et al: Accuracy and economics of RTU pregnancy detection, and comparisons with A-mode. North Carolina State University. Available at: http://mark.asci.ncsu.edu/Reproduction/rtu/armstrong.htm (accessed 1997).
tional savings are gained when producers are willing to institute a 100% culling policy, rather than a standard culling policy (cull after the second return to estrus). Open sows are culled immediately after pregnancy detection with the 100% culling policy. We have observed that many producers become very proficient with the use of real-time ultrasound techniques. These producers can diagnose pregnancy as early as day 23 (sometimes earlier). This proficiency is useful in assessing pregnancy status in breeding groups, when the test day includes animals at days 23 to 28 of gestation. It is not surprising that the greater benefits are gained with the use of real-time ultrasound scanning in large herds or as more sows are tested (Table 101-6). Again, the greatest benefits are gained when early testing is implemented in herds with low farrowing rates. The cost of an open day or nonproductive sow day (NPSD) varies from farm to farm. As the cost of an NPSD increases, the savings per sow with use of real-time ultrasonography also increase (Fig. 101-2). It also is evident that if real-time ultrasound scanning detects a greater percentage of open sows than is found with the traditional methods, then additional savings per sow will result. Real-time ultrasound scanning appears to be more versatile than the other methods of pregnancy diagnosis currently available. Besides pregnancy detection, it has been used to assess reproductive disorders in goats52 and to evaluate carcass characteristics in growing pigs.56 These findings lend further support to the potential for other uses for this technique in swine production. For instance, pseudopregnant sows and gilts with uteri containing mummified fetuses have been differentiated from pregnant sows.57 Recently, it was demonstrated that real-time ultrasound scanning is an effective technique to identify pseudopregnant sows between days 65 and 75 after
Dollar per sow
Table 101-6
771
$2.00/NPSD $1.50/NPSD $1.00/NPSD $.50/NPSD
3 2 1 0 1
2 3 4 Percent improvement
5
Fig. 101-2 Money saved per sow is influenced by both the percentage improvement and the cost of a nonproductive sow day (NPSD). The real-time ultrasound scanner was used at 23 days after mating, and the data are based on scanning 200 sows per week, with a 75% farrowing rate. The percentage improvement is based on a comparison of real-time ultrasound scanning at 23 days with amplitude-depth scanning at 28 and 35 days of gestation.
mating.58 Although the uterus of a pseudopregnant sow may contain fluid, the failure to observe fetal skeletons is indicative of pseudopregnancy. Furthermore, past research showed that this technique was useful to identify and distinguish sows and gilts with endometritis from females in later stages of pregnancy.57
SUMMARY AND CONCLUSIONS The advantages of sensitive and specific methods for early pregnancy diagnosis in swine include early detection of conception failure, forecasting production levels, and early identification of nonpregnant animals, which facilitates decisions regarding culling, treatment, or rebreeding. At present, detection of nonconceiving sows that return to estrus and use of amplitude-depth ultrasonography are the most widely used methods of pregnancy diagnosis. Despite routine use of these traditional methods, a common finding is that many sows either fail to farrow after being considered pregnant or return to estrus at irregular times during a presumed pregnancy. Perhaps the most promising technique for porcine pregnancy detection is real-time ultrasound scanning. This method is used routinely in a variety of species; however, applied research and improved technology have enhanced its applications in commercial sow farms. Perhaps the most intriguing aspect of real-time ultrasound scanning is that the user can visualize the uterus and its contents. Despite the obvious need for improved pregnancy diagnosis abilities for swine producers, little progress or changes were made until the development and application of real-time ultrasound techniques.
References 1. Almond GW, Dial GD: Pregnancy diagnosis in swine: principles, applications, and accuracy of available techniques. J Am Vet Med Assoc 1987;191:858–870.
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2. Signoret JP: Reproductive behavior of pigs. J Reprod Fertil Suppl 1970;11:105–117. 3. Jochle W, Schilling E: Improvement of conception rate and diagnosis of pregnancy in sows by an androgen-oestrogendepot preparation. J Reprod Fertil 1965;10:439–440. 4. Bosc MJ, Martinat-Botte F, Nicolle A: Etude de deux technique de diagnostic de gestation chez la truie. Ann Zootech 1975;24:651–660. 5. Almond GW, Dial GD: Pregnancy diagnosis in swine: a comparison of the accuracies of mechanical and endocrine tests with return to estrus. J Am Vet Med Assoc 1986;189:1567– 1571. 6. Moeljono MPE, Thatcher WW, Bazer FW: A study of prostaglandin F2 as the luteolysin in swine: II. Characterization and comparison of prostaglandin-F2, estrogens and progestin concentrations in utero-ovarian vein plasma of nonpregnant and pregnant gilts. Prostaglandins 1977;14: 543–555. 7. Bazer FW, Thatcher WW: Theory of maternal recognition of pregnancy in swine based upon oestrogen controlled endocrine versus exocrine secretions of prostaglandin-F2α by uterine endometrium. Prostaglandins 1977;14:397–401. 8. Bosc MJ, Martinat-Botte F, Terqui M: Practical uses of prostaglandins in pigs. Acta Vet Scand Suppl 1981;77: 209–226. 9. Perry JS, Heap RB, Burton RD, et al: Endocrinology of the blastocyst and its role in the establishment of pregnancy. J Reprod Fertil 1976;25(Suppl):85–104. 10. Ellendorff F, Meyer JN, Elsaesser F: Prospects and problems and fertility diagnosis in the pig by aid of progesterone determination. Br Vet J 1976;132:543–550. 11. Andersson AM, Einarsson S: Studies on the oestrus and ovarian activity during five successive oestrous cycles in gilts. Acta Vet Scand 1980;21:677–688. 12. Larsson K, Edqvist LE, Einarsson S, et al: Determination of progesterone in peripheral blood-plasma as a diagnostic aid in female swine. Nord Vet Med 1975;27:167–172. 13. Ellicott AR, Dziuk PJ: Minimum daily dose of progesterone and plasma concentration for maintenance of pregnancy in ovariectomized gilts. Biol Reprod 1973;9:300–304. 14. Sanders H, Rajamahendren R, Burton B: The development of a simple fecal immunoreactive progestin assay to monitor reproductive function in swine. Can Vet J 1994;35:355–358. 15. Hay Ma, King WA, Gartley CJ, et al: Correlation of periovulatory serum and fecal progestins in the domestic dog. Can J Vet Res 2000;64:59–63. 16. Hirata S, Mori Y: Monitoring reproductive status by fecal progesterone analysis in ruminants. J Vet Med Sci 1995;57: 845–850. 17. Robertson HA, Dwyer RJ, King GJ: Oestrogens in fetal and maternal fluids throughout pregnancy in the pig and comparisons with the ewe and cow. J Endocrinol 1985; 106:355–360. 18. Guthrie HD, Deaver DR: Estrone concentration in the peripheral plasma of pregnant and nonpregnant gilts. Theriogenology 1979;11:321–329. 19. Cunningham NF: Pregnancy diagnosis in sows based on serum oestrone sulphate concentration. Br Vet J 1982;138: 543–544. 20. Seren E, Mattioli M, Gaiani R, et al: Direct estimation of urine estrone conjugate for a rapid pregnancy diagnosis in sows. Theriogenology 1983;19:817–822. 21. Robertson HA, King GJ, Dyck GW: The appearance of oestrone sulphate in the peripheral plasma of the pig early in pregnancy. J Reprod Fertil 1978;52:337–338. 22. Cunningham NF, Hattersley JP, Wrathall AE: Pregnancy diagnosis in sows based on serum oestrone sulphate concentration. Vet Rec 1983;113:229–233.
23. Kensinger RS, Collier RJ, Bazer FW, et al: Effect of number of conceptuses on maternal hormone concentrations in the pig. J Anim Sci 1986;62:1666–1674. 24. Clarke FM, Morton H, Clunie CJA: Detection and separation of two serum factors responsible for depression of lymphocyte activity in pregnancy. Clin Exp Immunol 1978;32:318– 323. 25. Koch E, Ellendorff F: Prospects and limitations of the rosette inhibition test to detect activity of early pregnancy factor in the pig. J Reprod Fertil 1985;74:29–38. 26. Koch E, Morton H, Ellendorf F: Early pregnancy factor: biology and practical application. Br Vet J 1983;139:52–58. 27. Greco CR, Vivas AB, Bosch RA: Evaluation of the method for early pregnancy factor detection (EPF) in swine: significance in early pregnancy diagnosis. Acta Physiol Pharmacol Ther Latinoam 1992;42:43–50. 28. Rapic S: Radiological diagnosis of pregnancy in swine. Vet Rec 1961;21:171. 29. Wrathall AE, Bailey J, Hebert CN: A radiographic study of development of the appendicular skeleton in the fetal pig. Res Vet Sci 1974;17:154–168. 30. Cameron RDA: Pregnancy diagnosis in the sow by rectal examination. Aust Vet J 1977;53:432–435. 31. Wildt DE, Fujimoto S, Spencer JL, et al: Direct ovarian observation in the pig by means of laparoscopy. J Reprod Fertil 1973;35:541–543. 32. Wildt DE, Morcom CB, Dukelow WR: Laparoscopic pregnancy diagnosis and uterine fluid recovery in swine. J Reprod Fertil 1975;44:301–304. 33. Morton DB, Rankin JEF: The histology of the vaginal epithelium of the sow in oestrus and its use in pregnancy diagnosis. Vet Rec 1969;84:658–666. 34. Walker D: Pregnancy diagnosis in pigs. Vet Rec 1972;90: 139–144. 35. Williamson P, Hennessy D: An assessment of the vaginal biopsy technique of pregnancy diagnosis in sows. Aust Vet J 1975;51:91–93. 36. Done JT, Heard TW: Early pregnancy diagnosis in the sow by vaginal biopsy. Vet Rec 1968;82:64–68. 37. Fraser AF, Nagaratnam V, Callicott RB: The comprehensive use of Doppler ultrasound in farm animal reproduction. Vet Rec 1971;88:202–205. 38. Swensson T: Foetus sound detection for control of pregnancy in swine. Svensk Veterin 1978;30:781–783. 39. McCaughey WJ, Rea CC: Pregnancy diagnosis in sows: a comparison of the vaginal biopsy and Doppler ultrasound techniques. Vet Rec 1979;104:255–258. 40. Almond GW, Bosu WTK, King GJ: Pregnancy diagnosis in swine: a comparison of two ultrasound instruments. Can Vet J 1985;26:205–208. 41. Holtz W: Pregnancy detection in swine by pulse mode ultrasound. Anim Reprod Sci 1982;4:219–226. 42. Lindahl IL, Totsch JP, Martin PA, et al: Early diagnosis of pregnancy in sows by ultrasonic amplitude-depth analysis. J Anim Sci 1975;40:220–222. 43. Hansen LH, Christensen IJ: The accuracy of porcine pregnancy diagnosis by a newly developed ultrasonic A-scan tester. Br Vet J 1976;132:66–67. 44. Knight JW, Bazer FW, Thatcher WW, et al: Conceptus development in intact and unilaterally hysterectomizedovariectomized gilts: interrelationships among hormonal status, placental development, fetal fluids and fetal growth. J Anim Sci 1977;44:620–637. 45. Torbeck RL, Rautanen NW: Early pregnancy diagnosis in the mare with ultrasonography. J Equine Vet Sci 1982;2:204–207. 46. Pierson RA, Ginther OJ: Ultrasonography for detection of pregnancy and study of embryonic development in heifers. Theriogenology 1984;22:225–233.
Infertility Associated with Abnormalities of the Estrous Cycle and the Ovaries 47. Bondestam S, Alitalo I, Karkkainen M: Realtime ultrasound pregnancy diagnosis in the bitch. J Small Anim Pract 1983;24:145–151. 48. Inaba T, Nakazima Y, Matsui N, et al: Early pregnancy diagnosis in sows by ultrasonic linear electronic scanning. Theriogenology 1983;20:97–101. 49. Jackson GH: Pregnancy diagnosis in the sow using real-time ultrasonic scanning. Vet Rec 1986;119:90–91. 50. Buckrell BC, Bonnett BN, Johnson WH: The use of real-time ultrasound rectally for early pregnancy diagnosis in sheep. Theriogenology 1986;25:665–673. 51. Davey CG: An evaluation of pregnancy testing in sheep using a real-time ultrasound scanner. Aust Vet J 1986;63:347– 349. 52. Pieterse MC, Taverne MAM: Hydrometra in goats: diagnosis with real-time ultrasound and treatment with prostaglandins or oxytocin. Theriogenology 1986;26:813–821. 53. Botero O, Martinat-Botte F, Chevalier F: Ultrasonic echography for early pregnancy diagnosis in the sow. Proceedings of the 8th International Pig Veterinary Society Congress, Ghent, Belgium, 1984, p 306.
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54. Knox RV, Althouse GC: Visualizing the reproductive tract of the female pig using real-time ultrasonography. Swine Health Prod 1999;7:207–215. 55. Armstrong JD, Almond GW, White S, et al: Accuracy and economics of RTU pregnancy detection, and comparisons with A-mode. North Carolina State University. Available at: http://mark.asci.ncsu.edu/Reproduction/rtu/armstrong.htm (accessed 1997). 56. McLaren DG, McKeith FM, Novakofski J: Prediction of carcass characteristics at market weight from serial real-time ultrasound measures of backfat and loin eye area in growing pigs. J Anim Sci 1989;67:1657–1667. 57. Martinat-Botte F, Lepercq M, Forgerit Y, et al: Evaluation of swine embryonic growth by ultrasonography. Proceedings of the 9th International Pig Veterinary Society Congress, Barcelona, Spain, 1986, p 27. 58. Flowers WL: Real-time ultrasonography and diagnosis of pseudopregnancy in swine. North Carolina State University. Available at: http://mark.asci.ncsu.edu/Reproduction/rtu/ reprortu.htm (accessed 2001).
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Infertility Associated with Abnormalities of the Estrous Cycle and the Ovaries GLEN W. ALMOND
V
arious reports have demonstrated the role of infectious agents in porcine reproductive failure. For most infectious agents, researchers and veterinary practitioners have elucidated the pathogenesis, modes of transmission, and reasonably effective control programs. By contrast, porcine reproductive and respiratory syndrome virus (PRRSV) disease continues to be difficult to control, and the swine industry recognizes the economic impact of the virus on all phases of production. PRRSV disease continues to be detrimental to reproductive performance in sow herds, with variable severity of clinical signs in affected animals. With these widespread problems associated with PRRSV, pig producers often attribute reproductive failure to the virus when in fact the underlying causes are noninfectious. Unfortunately, the precise pathogenic mechanisms of noninfectious causes of repro-
ductive failure also are elusive, and the interactions between the various factors affecting reproduction create major challenges to any efforts to improve the performance of the breeding herd. Various investigators have examined the physiologic control of estrus, ovulation, conception, and pregnancy; however, the endocrine changes associated with these processes are more complex than was previously believed. Season, nutrition, environment, and management are well recognized for their potential to alter reproductive processes. In addition, recent studies revealed that various components of the immune system also possess profound roles in porcine reproduction. This chapter provides information regarding the physiologic mechanisms and “management” factors involved with infertility due to abnormalities of the porcine estrous cycle.