- Email: [email protected]
Ultrasound Determination of Fetal Gender
Ultrasound Determination of Fetal Gender 40. Drew ML, Alexander BM, Sasser RG: Pregnancy determination by use of pregnancy specific protein B radioimmunoassay in llamas. J Am Vet Med Assoc 1995;207:217. 41. Threlfall WR: Immunosuppressive early pregnancy factor (ISEPF) detection for pregnancy diagnosis in dairy cows. Theriogenology 1994;41:317. 42. Ginther OJ: Ultrasonic imaging and animal reproduction: Fundamentals, Book 1. Cross Plains, WI: Equiservices, 1995. 43. Boyd JS, Omran SN, Ayliffe TR: Use of a high frequency transducer with real time B-mode ultrasound scanning to identify very early pregnancy in cows. Vet Rec 1988;123:8. 44. Pierson RA, Ginther OJ: Ultrasonography for detection of pregnancy and study of embryonic development in heifers. Theriogenology 1984;22:225. 45. Kastelic JP, Curran S, Ginther OJ: Accuracy of ultrasonography for pregnancy diagnosis on days 10 to 22 in heifers. Theriogenology 1989;31:813.
CHAPTER
303
46. White IR, Russel AJF, Wright A, et al: Real-time ultrasonic scanning in the diagnosis of pregnancy and the estimation of gestational age in cattle. Vet Rec 1985;117:5. 47. Curran S, Pierson RS, Ginther OJ: Ultrasonographic appearance of the bovine conceptus from days 20 through 60. J Am Vet Med Assoc 1986;189:1295. 48. Kastelic JP, Curran S, Pierson RA, et al: Ultrasonic evaluation of the bovine conceptus. Theriogenology 1988;29:39. 49. Szenci O, Gyulai G, Nagy P, et al: Effects of uterus position relative to the pelvic inlet on the accuracy of early bovine pregnancy diagnosis by means of ultrasonography. Vet Q 1995;17:37. 50. Muller E, Wittkowski G: Visualization of male and female characteristics of bovine fetuses by real-time ultrasonics. Theriogenology 1986;25:571. 51. Curran S, Kastelic JP, Ginther OJ: Determining sex of the bovine fetus by ultrasonic assessment of the relative location of the genital tubercle. Anim Reprod Sci 1989;19:217.
40
Ultrasound Determination of Fetal Gender RODNEY A. CHRISTMAS and JILL COLLOTON
F
etal gender determination by real-time ultrasound evaluation has become a common reproductive management tool employed by both dairy and beef cow-calf operations. Other benefits of ultrasonography include early pregnancy diagnosis, diagnosis of fetal viability, twins and uterine pathology, and increased accuracy of ovarian structure identification.1–3 When fetal gender determination initially was utilized by beef cattle producers, the payback ratio was estimated to be at least 10 : 1 and sometimes as high as 100 : 1.4 It was thought at that time that the high profit margin probably was a result of the newness of the technology and that the procedure would remain profitable even after widespread acceptance. Those predictions have turned out to be accurate, because pregnant beef cows that are marketed with known-gendered fetuses routinely sell for $25 to $50 more per head than contemporaries with unknown fetal gender. Benefits of fetal gender determination for the dairy cow include the increased sale value of pregnant animals carrying heifers, ability to plan embryo transfer programs to fill bull contracts, cull decision information for marginal cows, and ability to predict replacement needs.
To accurately determine fetal gender, it is important that the practitioner have good-quality ultrasound equipment, an excellent understanding of fetal anatomy, and thorough training in reproductive ultrasonography. It also is important for practitioners to recognize the limitations of their ability, and of the technology itself, to ensure producer adoption of fetal gender identification. The reported accuracy of fetal gender determination approaches 100%.5 Under conditions of low light and calm cattle, this accuracy can be realized. Nevertheless, occasionally, despite the practitioner’s best effort, the necessary view cannot be obtained and therefore an accurate diagnosis cannot be made. In such instances it is imperative that the practitioner refrain from guessing; the producer should be informed of the limitations, and the examination be should be repeated in a few days. With experience, nondiagnostic examinations will occur with decreasing frequency.
EQUIPMENT A number of the ultrasound units available for purchase are more than adequate to identify fetal gender in cattle.
304
CHAPTER 40
Key areas of consideration in purchasing a scanner are image quality, portability, service, and power source. Image quality is determined by a complex set of factors. An ultrasound unit has two basic parts, both of which affect image quality: the transducer and the console.
nosis, but certain options may be desirable in some situations. Warranty and service. One-year warranties are standard for most ultrasound units. Turnaround time on repairs should be short, perhaps as quick as 48 hours. Some companies will provide a loaner unit during repair.
Transducer The number of elements of piezoelectric crystals in the transducer and the frequency of their vibration influence image quality. The number of crystals (or elements) in the transducer will be greater than 80 in most good machines. The frequency of vibration of the piezoelectric crystals is measured in megahertz (MHz). Transducers for bovine use commonly are available in frequencies of 3.5 MHz, 5 MHz, or 7.5 MHz. Lower-frequency transducers provide more depth of penetration but decreased resolution, so they are unsuitable for reproductive examinations. Higherfrequency transducers provide the best resolution but limit the depth of penetration, which may make scanning larger fetuses difficult. The standard transducer used in bovine reproductive ultrasonography has been the 5-MHz linear transducer, which we prefer in our practice. Some practitioners, however, prefer the increased resolution provided by the 7.5-MHz transducer. Transducers are available in different shapes: linear, curvilinear, or sector. This designation refers to how the piezoelectric crystals are arranged in the transducer. As the name implies, the linear transducers have the crystals arranged in the head of the transducer in a linear fashion. The curvilinear transducer has a bend in the linear arrangement, and the sector scanner has a single crystal that oscillates, providing a wedge-shaped image. The sector and curvilinear scanners are awkward for routine rectal examinations. At this time, almost all transducers currently available for bovine ultrasonography are linear.
Choosing an Ultrasound Unit Image quality is the most critical criterion in selecting an ultrasound unit. A quick way to determine image quality is to scan an ovary with a corpus luteum. The ovarian stroma should be easily differentiated from the luteal tissue. Beyond good image quality, personal preference will determine a practitioner’s choice of machine. The practitioner should try as many machine and transducer combinations as possible and then buy the one that feels the most comfortable and that has the best service contract.
Console The console should read at least 64 shades of gray. Most units have 256 shades of gray, but the human eye cannot detect anything greater than 64. The number of channels determines focusing ability. Twelve or more channels are adequate. Beyond 30 channels no visible difference will be noted.6 Other Components and Considerations Portability and power source. Ultrasound units for use in the bovine vary in weight from 2 to 35 pounds. The larger units require an outside power source and are designed to be placed on a cart. They are most suitable for situations in which the patient comes to the machine. The smaller portable units are battery operated and are designed to be worn on the person. These are ideal when mobility is required. Image display. Units may have a screen display, goggles, or both. Screen displays are useful when more than one person wishes to view the scan. Goggles are helpful when working outdoors or in bright light. Additional options. Fetal aging software, image recording abilities, dual screen display, cine mode, Mmode, and color Doppler are just a few options available on some machines. None are critical for fetal gender diag-
ANATOMIC LANDMARKS The genital tubercle is the prime structure that needs to be identified during an ultrasonographic examination for fetal gender. In the female, the genital tubercle will develop into the clitoris, so it is always located just below the tailhead. The male genital tubercle will develop into the penis, so it is always located immediately behind the umbilical cord. The male and female genital tubercles can be identified as early as day 55 using ultrasound examination.5 The gestational period during which fetal sexing is most accurate is 60 to 80 days.7 Before 60 days, the fetus may not be adequately developed; after 80 days, the ultrasound energy may not adequately penetrate maternal tissue to reach the fetus, especially in large dairy cows and overconditioned heifers. Figure 40-1 is a photograph of an 80-day-gestation bovine male fetus, with arrows demonstrating the important anatomic landmarks, foot, umbilicus, genital tubercle, and scrotum for fetal gender identification. Figure 40-2 presents a view of the
A
C
D
B Fig. 40-1 Ultrasound view of the ventral surface of an 80-day bovine male fetus. A, Front foot; B, umbilicus; C, genital tubercle; D, scrotum.
Ultrasound Determination of Fetal Gender
A
Fig. 40-2 Hindquarters of 75-day female fetus. A female genital tubercle is recognizable.
hindquarters of 75-day-gestation female fetus, with the female genital tubercle identified by the letter A. Other key landmarks include the head, the caudal-tocranial taper of the thoracic cavity, the fetal heart, and the fetal stomach and liver. These landmarks give the practitioner a cranial-to-caudal orientation to evaluate which direction the probe should be moved for imaging the genital tubercle. Teats or scrotum also may be seen, especially on fetuses more than 75 days in gestation, but diagnosis of fetal gender should not be based on identification of these structures alone. To have a reasonable chance at becoming proficient at ultrasonographic fetal gender determination, it is critical that the practitioner have an in-depth knowledge of fetal anatomy so that the images received from the ultrasound machine can be accurately interpreted.
GETTING THE IMAGE After familiarization with fetal anatomy and the critical structures, it is time to make sense of the snowlike images on the screen. Often, the biggest struggle is breaking out of palpation mode, because most practitioners find ultrasound interrogation to be a very different skill from palpation. The transition from tactile to visual diagnosis can be difficult, especially for experienced palpators. In fact, good palpation skills are helpful, but not critical, to develop good ultrasonography skills. Ultrasound is a great teaching tool for novice palpators because they can “see” what they were just feeling. Faith and patience are the two keys in starting to image the reproductive tract of cattle, and in particular when the goal is to identify fetal gender. This section summarizes the basic examination points. The goal of the examination to determine fetal gender is to identify a gender-specific structure: the genital tubercle. The genital tubercle is composed of highly echogenic (bright white on screen) tissue and usually appears
305
bilobed. In the male, the genital tubercle will be located just caudal to the umbilicus, and in the female, just ventral to the tail. Refer back to Figures 40-1 and 40-2 for orientation. Individual clinicians will develop their own imaging technique as they gain experience. Some prefer to first palpate the uterus and retract it into the pelvic cavity; others, ourselves included, prefer not to palpate and instead immediately scan the uterus. The key is to develop a systematic and efficient approach. The first step is to obtain cranial-to-caudal orientation by visualizing the head, beating heart, and the umbilicus. Unlike a radiograph, the ultrasound image represents only a thin cross-section of the tissues directly below the transducer. Accordingly, the transducer must be moved to find and identify the location of structures. To center the image on the screen, the transducer must be moved forward and backward. Once the fetus is centered, the transducer can be moved very slowly sideways in both directions to locate the genital tubercle. Once the ultrasound operator is oriented, one of three basic views can be used to examine the fetus: a lateral view, a frontal view, and a cross-sectional view. Of these basic views, the cross-sectional view, is the most commonly used and easiest view to obtain. If a cross-sectional view is obtained, the transducer should be moved through the fetus to the umbilical attachment in the ventral abdomen and then moved slowly back and forth to diagnose the presence or absence of the male genital tubercle just caudal to the umbilicus. The genital tubercle will always be more echogenic than the umbilicus. If a male genital tubercle is noted, the examination is concluded. If the male genital tubercle is not conclusively identified the transducer should be advanced through the fetus to the perineal region. These simple manipulations sound easy in theory, but in practice the perineal area is relatively difficult to image because it often is obscured by the uterine wall or a placentome. It also is important to be able to distinguish the highly echogenic coccygeal vertebrae of the tail from the genital tubercle. In an oblique view, the pin bones also may be mistaken for the female genital tubercle. In general, the female genital tubercle will be bilobed or trilobed, and the tail or pin bones are monolobed. Another common reason for an incorrect identification of a female as a male is a fetal position in which the bright, echogenic tip of the tail is tucked between the hind legs.8,9 The frontal view is a little more difficult to obtain than the cross-sectional view but is the easiest to orient and in our experience provides the clearest view of the genital tubercle and other gender-specific anatomic structures. The ultrasound appearance of the female genital tubercle in the frontal view of the perineal region is demonstrated in Figure 40-3. A similar view of a male fetus is shown in Figure 40-4 demonstrating the scrotum. The lateral view is the least commonly used for fetal gender identification. The male genital tubercle may be obscured by the legs in this view. It also is more difficult to view the female genital tubercle. For these reasons, we rarely use this image. Key points in the ultrasound examination are summarized in Box 40-1. Table 40-1 presents a sample worksheet for recording the ultrasound findings.
306
CHAPTER 40
B
B
A
B
A Fig. 40-3 Ultrasound view of the hindquarter of a 75-day
Fig. 40-4 Ultrasound view of the hindquarters of a 80-day
female bovine fetus.
male fetus. Image was obtained using a 5-MHz linear probe. The dorsal surface of the fetus is to the left in the figure. A, Right thigh; B, trilobed scrotum.
Table 40-1 Fetal Age and Sexing Worksheet Itsa Bullorheifer, DVM Ultrasound Services, Inc./LLC 123-555-6789 Date: _______________ Client: __________________________________________
ID
Date Bred or Fetal Age
Predicted Sex
Expected Calving Date
Comments
Research indicates that fetal sexing is 95–99% accurate. Because of variability in fetal size and gestation length between animals, calving dates may deviate up to 1 month from fetal age measurements. Although no research indicates that ultrasound is harmful to the fetus, no warranty is made for fetal viability beyond the date of examination. No warranty is made on fetal sex determination or fetal aging. Adapted from Colloton JD: American Association of Bovine Practitioners Seminar on Bovine Ultrasonography Notes. Vancouver, BC, Canada, September 2001.
SUMMARY Achieving technical competence in ultrasonographic fetal gender determination will require (1) a high-quality ultrasound unit, (2) a detailed understanding and comprehension of ultrasonographic fetal anatomy, and (3) the skill to manipulate the ultrasound transducer to get a
well-positioned, adequately focused image. The first two of these requirements are relatively easy to achieve; the third requires practice and patience. It is important to make the investment in training both through video tapes and in participation in “wet labs” and seminars. With commitment and the requisite investment, professional competence can be achieved.
Induced Abortion
307
References
Box 40-1 Fetal Sexing by Ultrasonographic Evaluation: Key Points 1. Fetal age: 60 to 80 days of gestation. The ultrasound examination can be performed as early as day 55 and as late as day 110. 2. Diagnosis is based only on the identification of the genital tubercle or gender-specific structure such as the penis. 3. Move the transducer in a slow, controlled fashion. 4. Keep your eye on the screen all the time, because sometimes structures move by quickly. 5. Locate the umbilicus and move caudally. 6. If possible, roll the transducer under the uterus to provide the best contact between the transducer and the fetus, for optimal focus and clarity. 7. Check for twins during the examination. 8. Keep careful records of the findings (see Table 40-1). 9. Stay relaxed, and focus on making smooth, controlled movements with the transducer.
CHAPTER
1. Beal WE, Perry RC, Corah LR: The use of ultrasound in monitoring reproductive physiology of beef cattle. J Anim Sci 1992;70:924–929. 2. Colloton J: Incorporating ultrasound into bovine practice. eSeminar on Bovine Ultrasound. Proceedings of the 29th Annual Meeting of the American Association of Bovine Practitioners, 2001, pp 1–12. 3. Müller E, Wittkowski J: Visualization of male and female characteristics of bovine fetuses by real-time ultrasonics. Theriogenology 1986;25:571–574. 4. Stroud BK: Clinical applications of bovine reproductive ultrasonography. Comp Contin Educ Pract Vet 1994;16:1085–1097. 5. Curran S, Kastilic JP, Ginther OJ: Determining sex of the bovine fetus by ultrasonic assessment of the relative location of the genital tubercle. Anim Reprod Sci 1989;19:217–227. 6. Raphael Bloom, Veterinary Sales and Service, Stuart, FL: Personal correspondence, 2004. 7. Ginther OJ, Curran S, Ginther M: Fetal gender determination in cattle and horses. Video. Cross Plains, WI: Equiservices, 1995. 8. Stroud BK: Bovine reproductive ultrasonography: A video training tutorial. Weatherford, TX, 1994. 9. Stroud BK: Bovine ultrasound fetal sexing: Unedited tutorial. 52: Head. Weatherford, TX, 1994.
41
Induced Abortion PHILIP G. A. THOMAS
T
herapeutic abortion may be indicated during normal or abnormal pregnancy in the cow. Misidentification of a breeding female, accidental breeding of a very young heifer, and unwanted pregnancy in feedlot heifers are indications for abortion during normal gestation. Induced abortion can be included in treatment protocols for pathologic conditions of pregnancy, including fetal maceration, fetal mummification, hydramnios, and hydroallantois.
PHYSIOLOGY OF PREGNANCY MAINTENANCE Gestation in the cow extends 270 to 292 days after breeding. Once conception has occurred, progesterone is essential for pregnancy maintenance. Both luteal and extraovarian sources of progesterone must be eliminated for successful induction of abortion. Although the maternal endocrine events of the first 15 days of cycle and of
pregnancy are similar, the conceptus secretes a range of products, including steroids, prostaglandins, and proteins, beginning at 12 to 13 days of gestation. At least one of these products, interferon-γ, results in maternal recognition of pregnancy by inhibition of luteolysis and prolonged luteal lifespan.1–3 These effects are mediated by attenuation of endogenous prostaglandin F2 alpha (PGF2α) secretion.4 The functional life of the corpus luteum (CL) is controlled by a balance of luteotropic factors, including luteinizing hormone, and luteolytic factors, including PGF2α. PGF2α is the naturally occurring luteolysin, acting both directly and indirectly on the CL. PGF2α may cause local vasoconstriction of luteal blood flow; however, PGF2α receptors are present on luteal cells, and PGF2α has a direct effect on luteal progesterone secretion.5 Endogenous luteolysis occurs in response to a cascade of hormonal events that result in pulsatile PGF2α secretion. It has been proposed that as part of this cascade, estradiol
CHAPTER
303
46. White IR, Russel AJF, Wright A, et al: Real-time ultrasonic scanning in the diagnosis of pregnancy and the estimation of gestational age in cattle. Vet Rec 1985;117:5. 47. Curran S, Pierson RS, Ginther OJ: Ultrasonographic appearance of the bovine conceptus from days 20 through 60. J Am Vet Med Assoc 1986;189:1295. 48. Kastelic JP, Curran S, Pierson RA, et al: Ultrasonic evaluation of the bovine conceptus. Theriogenology 1988;29:39. 49. Szenci O, Gyulai G, Nagy P, et al: Effects of uterus position relative to the pelvic inlet on the accuracy of early bovine pregnancy diagnosis by means of ultrasonography. Vet Q 1995;17:37. 50. Muller E, Wittkowski G: Visualization of male and female characteristics of bovine fetuses by real-time ultrasonics. Theriogenology 1986;25:571. 51. Curran S, Kastelic JP, Ginther OJ: Determining sex of the bovine fetus by ultrasonic assessment of the relative location of the genital tubercle. Anim Reprod Sci 1989;19:217.
40
Ultrasound Determination of Fetal Gender RODNEY A. CHRISTMAS and JILL COLLOTON
F
etal gender determination by real-time ultrasound evaluation has become a common reproductive management tool employed by both dairy and beef cow-calf operations. Other benefits of ultrasonography include early pregnancy diagnosis, diagnosis of fetal viability, twins and uterine pathology, and increased accuracy of ovarian structure identification.1–3 When fetal gender determination initially was utilized by beef cattle producers, the payback ratio was estimated to be at least 10 : 1 and sometimes as high as 100 : 1.4 It was thought at that time that the high profit margin probably was a result of the newness of the technology and that the procedure would remain profitable even after widespread acceptance. Those predictions have turned out to be accurate, because pregnant beef cows that are marketed with known-gendered fetuses routinely sell for $25 to $50 more per head than contemporaries with unknown fetal gender. Benefits of fetal gender determination for the dairy cow include the increased sale value of pregnant animals carrying heifers, ability to plan embryo transfer programs to fill bull contracts, cull decision information for marginal cows, and ability to predict replacement needs.
To accurately determine fetal gender, it is important that the practitioner have good-quality ultrasound equipment, an excellent understanding of fetal anatomy, and thorough training in reproductive ultrasonography. It also is important for practitioners to recognize the limitations of their ability, and of the technology itself, to ensure producer adoption of fetal gender identification. The reported accuracy of fetal gender determination approaches 100%.5 Under conditions of low light and calm cattle, this accuracy can be realized. Nevertheless, occasionally, despite the practitioner’s best effort, the necessary view cannot be obtained and therefore an accurate diagnosis cannot be made. In such instances it is imperative that the practitioner refrain from guessing; the producer should be informed of the limitations, and the examination be should be repeated in a few days. With experience, nondiagnostic examinations will occur with decreasing frequency.
EQUIPMENT A number of the ultrasound units available for purchase are more than adequate to identify fetal gender in cattle.
304
CHAPTER 40
Key areas of consideration in purchasing a scanner are image quality, portability, service, and power source. Image quality is determined by a complex set of factors. An ultrasound unit has two basic parts, both of which affect image quality: the transducer and the console.
nosis, but certain options may be desirable in some situations. Warranty and service. One-year warranties are standard for most ultrasound units. Turnaround time on repairs should be short, perhaps as quick as 48 hours. Some companies will provide a loaner unit during repair.
Transducer The number of elements of piezoelectric crystals in the transducer and the frequency of their vibration influence image quality. The number of crystals (or elements) in the transducer will be greater than 80 in most good machines. The frequency of vibration of the piezoelectric crystals is measured in megahertz (MHz). Transducers for bovine use commonly are available in frequencies of 3.5 MHz, 5 MHz, or 7.5 MHz. Lower-frequency transducers provide more depth of penetration but decreased resolution, so they are unsuitable for reproductive examinations. Higherfrequency transducers provide the best resolution but limit the depth of penetration, which may make scanning larger fetuses difficult. The standard transducer used in bovine reproductive ultrasonography has been the 5-MHz linear transducer, which we prefer in our practice. Some practitioners, however, prefer the increased resolution provided by the 7.5-MHz transducer. Transducers are available in different shapes: linear, curvilinear, or sector. This designation refers to how the piezoelectric crystals are arranged in the transducer. As the name implies, the linear transducers have the crystals arranged in the head of the transducer in a linear fashion. The curvilinear transducer has a bend in the linear arrangement, and the sector scanner has a single crystal that oscillates, providing a wedge-shaped image. The sector and curvilinear scanners are awkward for routine rectal examinations. At this time, almost all transducers currently available for bovine ultrasonography are linear.
Choosing an Ultrasound Unit Image quality is the most critical criterion in selecting an ultrasound unit. A quick way to determine image quality is to scan an ovary with a corpus luteum. The ovarian stroma should be easily differentiated from the luteal tissue. Beyond good image quality, personal preference will determine a practitioner’s choice of machine. The practitioner should try as many machine and transducer combinations as possible and then buy the one that feels the most comfortable and that has the best service contract.
Console The console should read at least 64 shades of gray. Most units have 256 shades of gray, but the human eye cannot detect anything greater than 64. The number of channels determines focusing ability. Twelve or more channels are adequate. Beyond 30 channels no visible difference will be noted.6 Other Components and Considerations Portability and power source. Ultrasound units for use in the bovine vary in weight from 2 to 35 pounds. The larger units require an outside power source and are designed to be placed on a cart. They are most suitable for situations in which the patient comes to the machine. The smaller portable units are battery operated and are designed to be worn on the person. These are ideal when mobility is required. Image display. Units may have a screen display, goggles, or both. Screen displays are useful when more than one person wishes to view the scan. Goggles are helpful when working outdoors or in bright light. Additional options. Fetal aging software, image recording abilities, dual screen display, cine mode, Mmode, and color Doppler are just a few options available on some machines. None are critical for fetal gender diag-
ANATOMIC LANDMARKS The genital tubercle is the prime structure that needs to be identified during an ultrasonographic examination for fetal gender. In the female, the genital tubercle will develop into the clitoris, so it is always located just below the tailhead. The male genital tubercle will develop into the penis, so it is always located immediately behind the umbilical cord. The male and female genital tubercles can be identified as early as day 55 using ultrasound examination.5 The gestational period during which fetal sexing is most accurate is 60 to 80 days.7 Before 60 days, the fetus may not be adequately developed; after 80 days, the ultrasound energy may not adequately penetrate maternal tissue to reach the fetus, especially in large dairy cows and overconditioned heifers. Figure 40-1 is a photograph of an 80-day-gestation bovine male fetus, with arrows demonstrating the important anatomic landmarks, foot, umbilicus, genital tubercle, and scrotum for fetal gender identification. Figure 40-2 presents a view of the
A
C
D
B Fig. 40-1 Ultrasound view of the ventral surface of an 80-day bovine male fetus. A, Front foot; B, umbilicus; C, genital tubercle; D, scrotum.
Ultrasound Determination of Fetal Gender
A
Fig. 40-2 Hindquarters of 75-day female fetus. A female genital tubercle is recognizable.
hindquarters of 75-day-gestation female fetus, with the female genital tubercle identified by the letter A. Other key landmarks include the head, the caudal-tocranial taper of the thoracic cavity, the fetal heart, and the fetal stomach and liver. These landmarks give the practitioner a cranial-to-caudal orientation to evaluate which direction the probe should be moved for imaging the genital tubercle. Teats or scrotum also may be seen, especially on fetuses more than 75 days in gestation, but diagnosis of fetal gender should not be based on identification of these structures alone. To have a reasonable chance at becoming proficient at ultrasonographic fetal gender determination, it is critical that the practitioner have an in-depth knowledge of fetal anatomy so that the images received from the ultrasound machine can be accurately interpreted.
GETTING THE IMAGE After familiarization with fetal anatomy and the critical structures, it is time to make sense of the snowlike images on the screen. Often, the biggest struggle is breaking out of palpation mode, because most practitioners find ultrasound interrogation to be a very different skill from palpation. The transition from tactile to visual diagnosis can be difficult, especially for experienced palpators. In fact, good palpation skills are helpful, but not critical, to develop good ultrasonography skills. Ultrasound is a great teaching tool for novice palpators because they can “see” what they were just feeling. Faith and patience are the two keys in starting to image the reproductive tract of cattle, and in particular when the goal is to identify fetal gender. This section summarizes the basic examination points. The goal of the examination to determine fetal gender is to identify a gender-specific structure: the genital tubercle. The genital tubercle is composed of highly echogenic (bright white on screen) tissue and usually appears
305
bilobed. In the male, the genital tubercle will be located just caudal to the umbilicus, and in the female, just ventral to the tail. Refer back to Figures 40-1 and 40-2 for orientation. Individual clinicians will develop their own imaging technique as they gain experience. Some prefer to first palpate the uterus and retract it into the pelvic cavity; others, ourselves included, prefer not to palpate and instead immediately scan the uterus. The key is to develop a systematic and efficient approach. The first step is to obtain cranial-to-caudal orientation by visualizing the head, beating heart, and the umbilicus. Unlike a radiograph, the ultrasound image represents only a thin cross-section of the tissues directly below the transducer. Accordingly, the transducer must be moved to find and identify the location of structures. To center the image on the screen, the transducer must be moved forward and backward. Once the fetus is centered, the transducer can be moved very slowly sideways in both directions to locate the genital tubercle. Once the ultrasound operator is oriented, one of three basic views can be used to examine the fetus: a lateral view, a frontal view, and a cross-sectional view. Of these basic views, the cross-sectional view, is the most commonly used and easiest view to obtain. If a cross-sectional view is obtained, the transducer should be moved through the fetus to the umbilical attachment in the ventral abdomen and then moved slowly back and forth to diagnose the presence or absence of the male genital tubercle just caudal to the umbilicus. The genital tubercle will always be more echogenic than the umbilicus. If a male genital tubercle is noted, the examination is concluded. If the male genital tubercle is not conclusively identified the transducer should be advanced through the fetus to the perineal region. These simple manipulations sound easy in theory, but in practice the perineal area is relatively difficult to image because it often is obscured by the uterine wall or a placentome. It also is important to be able to distinguish the highly echogenic coccygeal vertebrae of the tail from the genital tubercle. In an oblique view, the pin bones also may be mistaken for the female genital tubercle. In general, the female genital tubercle will be bilobed or trilobed, and the tail or pin bones are monolobed. Another common reason for an incorrect identification of a female as a male is a fetal position in which the bright, echogenic tip of the tail is tucked between the hind legs.8,9 The frontal view is a little more difficult to obtain than the cross-sectional view but is the easiest to orient and in our experience provides the clearest view of the genital tubercle and other gender-specific anatomic structures. The ultrasound appearance of the female genital tubercle in the frontal view of the perineal region is demonstrated in Figure 40-3. A similar view of a male fetus is shown in Figure 40-4 demonstrating the scrotum. The lateral view is the least commonly used for fetal gender identification. The male genital tubercle may be obscured by the legs in this view. It also is more difficult to view the female genital tubercle. For these reasons, we rarely use this image. Key points in the ultrasound examination are summarized in Box 40-1. Table 40-1 presents a sample worksheet for recording the ultrasound findings.
306
CHAPTER 40
B
B
A
B
A Fig. 40-3 Ultrasound view of the hindquarter of a 75-day
Fig. 40-4 Ultrasound view of the hindquarters of a 80-day
female bovine fetus.
male fetus. Image was obtained using a 5-MHz linear probe. The dorsal surface of the fetus is to the left in the figure. A, Right thigh; B, trilobed scrotum.
Table 40-1 Fetal Age and Sexing Worksheet Itsa Bullorheifer, DVM Ultrasound Services, Inc./LLC 123-555-6789 Date: _______________ Client: __________________________________________
ID
Date Bred or Fetal Age
Predicted Sex
Expected Calving Date
Comments
Research indicates that fetal sexing is 95–99% accurate. Because of variability in fetal size and gestation length between animals, calving dates may deviate up to 1 month from fetal age measurements. Although no research indicates that ultrasound is harmful to the fetus, no warranty is made for fetal viability beyond the date of examination. No warranty is made on fetal sex determination or fetal aging. Adapted from Colloton JD: American Association of Bovine Practitioners Seminar on Bovine Ultrasonography Notes. Vancouver, BC, Canada, September 2001.
SUMMARY Achieving technical competence in ultrasonographic fetal gender determination will require (1) a high-quality ultrasound unit, (2) a detailed understanding and comprehension of ultrasonographic fetal anatomy, and (3) the skill to manipulate the ultrasound transducer to get a
well-positioned, adequately focused image. The first two of these requirements are relatively easy to achieve; the third requires practice and patience. It is important to make the investment in training both through video tapes and in participation in “wet labs” and seminars. With commitment and the requisite investment, professional competence can be achieved.
Induced Abortion
307
References
Box 40-1 Fetal Sexing by Ultrasonographic Evaluation: Key Points 1. Fetal age: 60 to 80 days of gestation. The ultrasound examination can be performed as early as day 55 and as late as day 110. 2. Diagnosis is based only on the identification of the genital tubercle or gender-specific structure such as the penis. 3. Move the transducer in a slow, controlled fashion. 4. Keep your eye on the screen all the time, because sometimes structures move by quickly. 5. Locate the umbilicus and move caudally. 6. If possible, roll the transducer under the uterus to provide the best contact between the transducer and the fetus, for optimal focus and clarity. 7. Check for twins during the examination. 8. Keep careful records of the findings (see Table 40-1). 9. Stay relaxed, and focus on making smooth, controlled movements with the transducer.
CHAPTER
1. Beal WE, Perry RC, Corah LR: The use of ultrasound in monitoring reproductive physiology of beef cattle. J Anim Sci 1992;70:924–929. 2. Colloton J: Incorporating ultrasound into bovine practice. eSeminar on Bovine Ultrasound. Proceedings of the 29th Annual Meeting of the American Association of Bovine Practitioners, 2001, pp 1–12. 3. Müller E, Wittkowski J: Visualization of male and female characteristics of bovine fetuses by real-time ultrasonics. Theriogenology 1986;25:571–574. 4. Stroud BK: Clinical applications of bovine reproductive ultrasonography. Comp Contin Educ Pract Vet 1994;16:1085–1097. 5. Curran S, Kastilic JP, Ginther OJ: Determining sex of the bovine fetus by ultrasonic assessment of the relative location of the genital tubercle. Anim Reprod Sci 1989;19:217–227. 6. Raphael Bloom, Veterinary Sales and Service, Stuart, FL: Personal correspondence, 2004. 7. Ginther OJ, Curran S, Ginther M: Fetal gender determination in cattle and horses. Video. Cross Plains, WI: Equiservices, 1995. 8. Stroud BK: Bovine reproductive ultrasonography: A video training tutorial. Weatherford, TX, 1994. 9. Stroud BK: Bovine ultrasound fetal sexing: Unedited tutorial. 52: Head. Weatherford, TX, 1994.
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Induced Abortion PHILIP G. A. THOMAS
T
herapeutic abortion may be indicated during normal or abnormal pregnancy in the cow. Misidentification of a breeding female, accidental breeding of a very young heifer, and unwanted pregnancy in feedlot heifers are indications for abortion during normal gestation. Induced abortion can be included in treatment protocols for pathologic conditions of pregnancy, including fetal maceration, fetal mummification, hydramnios, and hydroallantois.
PHYSIOLOGY OF PREGNANCY MAINTENANCE Gestation in the cow extends 270 to 292 days after breeding. Once conception has occurred, progesterone is essential for pregnancy maintenance. Both luteal and extraovarian sources of progesterone must be eliminated for successful induction of abortion. Although the maternal endocrine events of the first 15 days of cycle and of
pregnancy are similar, the conceptus secretes a range of products, including steroids, prostaglandins, and proteins, beginning at 12 to 13 days of gestation. At least one of these products, interferon-γ, results in maternal recognition of pregnancy by inhibition of luteolysis and prolonged luteal lifespan.1–3 These effects are mediated by attenuation of endogenous prostaglandin F2 alpha (PGF2α) secretion.4 The functional life of the corpus luteum (CL) is controlled by a balance of luteotropic factors, including luteinizing hormone, and luteolytic factors, including PGF2α. PGF2α is the naturally occurring luteolysin, acting both directly and indirectly on the CL. PGF2α may cause local vasoconstriction of luteal blood flow; however, PGF2α receptors are present on luteal cells, and PGF2α has a direct effect on luteal progesterone secretion.5 Endogenous luteolysis occurs in response to a cascade of hormonal events that result in pulsatile PGF2α secretion. It has been proposed that as part of this cascade, estradiol