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2011, Vol. 6 No. 2, Article 88

 

Real-Time Ultrasonography as a Diagnostic Tool
in Bovine Reproduction

M. M. Pathan* and Z. A. Pampori1

 

Dairy Cattle Physiology Division,
National Dairy Research Institute Karnal, Haryana-132001

1College of Veterinary Sci. & A. H., SKUAST, Kashmir

 

*Corresponding Author; e-mail address: drmohsinvets@gmail.com

 


ABSTRACT

Assessment of the onset of estrus and time of ovulation, early pregnancy diagnosis and fetometry to estimate fetal age as well as progression of fetal growth, diagnosis of pregnancy disorders, course of uterine involution and uterine disorders (endometritis, pyometra, hydrometra) are factors/functions that need to be closely monitored in order to augment the reproductive efficiency of cattle. Transrectal real-time ultrasonography has proved to be a rapid and reliable technique for studying such reproductive functions in bovines. It provides information for better management of dairy herds.
Study of follicular dynamics and follicular structures help veterinarians to understand reproductive cycle and provides information to decide the correct line of treatment for ovarian pathological conditions. Ultrasonographic imaging of uterus helps to access the pregnancy status, involution of uterus after parturition and various pathological condition of uterus. Ultrasonography has proved its worth in improving the efficiency of recent gynecological technique like artificial insemination and embryo transfer. There is still a great potential for the continued application of this technology to further improve our understanding of the reproductive processes, disease diagnosis and to maximize reproductive efficiency of the bovine species.

KEY WORDS

Ultrasonography, diagnostic tool , bovine reproduction.

INTRODUCTION

Trans-rectal real-time B-mode ultrasonography is being routinely used as research and diagnostic tool in bovine reproduction. Real-time ultrasonic imaging provides a noninvasive technique to image directly, in situ, the internal and external anatomy of reproductive organs and tissues, and to characterize reproductive events (e.g., ovulation, transition of the uterus from a diestrous to an estrous echotexture). The technique is noninvasive, relatively simple and effective. By using real-time ultrasonography, it is possible to examine the individual ovary and follicular dynamics on a daily basis. Ultrasonographic images reveal that the growth of follicles in bovine ovaries occurs in a wave-like manner with two or three waves per estrous cycle. Different types of structure develop on the ovary like corpora lutea, follicles, follicular and luteal cysts and ovarian tumors, which are difficult to diagnose by manual per-rectal palpation. These can easily and accurately be diagnosed by using ultrasonography. To improve the reproductive performance of cow, it is necessary to inseminate at perfect time to improve the chance of fertilization. For this, it is necessary to correctly assess the onset of estrus and time of ovulation which can be accomplished by rectal ultrasonography. Early pregnancy diagnosis, fetometry to estimate fetal age and assessment of progression of fetal growth, diagnosis of pregnancy disorders and fetal sexing can be accurately done by using ultrasonography. The course of uterine involution and uterine disorders (endometritis, pyometra, hydrometra) can be monitored by ultrasonography (Kahn and Ludlow, 1989).

ULTRASONOGRAPHY MACHINE FOR VETERINARY APPLICATION

Audible sounds are of the order 20-20,000 Hz. Ultrasound is a high frequency sound wave above the audible range. For diagnostic applications, ultrasound waves of 1-10 MHz frequencies are employed. Like audible sound, ultrasound cannot propagate in vacuum and its transmission in gas is poor. A suitable coupling agent must bridge the gap between the transducer (which emits and receives ultrasound signals) and the patient skin. Ultrasound can be propagated in an elastic medium primary as longitudinal compression waves. By means of the echo primp; an image can be produced on the display screen. By means of the piezo electric effect, the piezo electric crystals in the transducer vibrate when a high voltage electrical current is applied. The magnitude of the vibration is proportional to the applied voltages, which indicate the power of the ultrasound beam. The frequency of the vibration of the ultrasound waves is related to primarily crystal characteristics. Ultrasound is transmitted to the patient form the transducer and propagated through the tissues. The velocity of propagation depends on the tissue characteristics. A proportion of sound waves reflected back to the transducer is converted to electric current and displayed as an echo on the ultrasound-viewing screen. The transducer, therefore, acts as both the sender and receiver of echoes.
Most ultrasound scanners used in bovine reproduction are linear-array, real-time, B-mode (brightness modality). Most ultrasound machines consist of a console unit that contains the electronics controls, a screen upon which the operator visualizes the ultrasound image and a transducer, which emits and receives high-frequency ultrasound waves. In B-mode ultrasonography, the image is a two-dimensional display of dots (pixels), the brightness of the dots is proportional to the amplitude of the reflected echoes returning to the transducer. Real-time refers as the ability to display movement of the organs (e.g. fetal heartbeat or intestinal motion). Ultrasound scanners are equipped with transducers of varying frequencies. The most commonly used frequencies in bovine reproduction are 3.5, 5.0 and 7.5 MHz. The higher the frequency of the transmitted sound waves, the better the image resolution, but the shallower the depth of penetration (Reeves et al, 1984). For routine bovine reproductive ultrasonography (early pregnancy diagnosis, pathology of the ovaries and uterus, fetal sexing etc), a 5 MHz linear rectal transducer seem to be the most versatile and effective. However, a 7.5 MHz linear transducer is recommended for follicular dynamics studies. For transvaginal oocyte recoveries, a convex-linear transducer gives better results. There are two types of scanners; linear array and sector. Linear-array transducers consist of a series of piezo electric crystals arranged in a row. The configuration of a linear-array transducer results in a rectangular image on the screen. Sector transducers, on the other hand, have only a few such crystals and the image produced is pie-shaped. Recent ultrasound scanners have a wider frequency range and accept a full line of single and dual frequency probes. Digital image port for computer image storage is also available. Battery-powered portable ultrasound scanners are also currently available. Doppler ultrasonography, which detects turbulence within blood vessels and direction of flow, is also a useful diagnostic tool. The Doppler phenomenon is the change in sound frequency of a moving object as perceived by a stationary observer. Doppler ultrasound machines detect frequency change and, therefore, movement, which is converted to an audible signal (Peter et al, 1992).
Techniques
The most common approach for scanning bovine reproductive organs is per rectum, using a transrectal transducer and a linear-array scanner. Transvaginal scanning is performed, usually with sector transducers, for certain special applications. For per-rectum ultrasound scanning in cattle, no sedation is indicated as the procedure is totally non-invasive and well tolerated, however adequate restraint is required. All feaces from the rectum should be evacuated prior to introduction of the transducer. The transducer face is lubricated with a suitable coupling medium and is usually covered by a lubricated plastic sleeve. It is then progressed cranially along the rectal floor to overlie the reproductive tract. The transducer face must be pressed firmly against the rectal mucosa in order to effect ultrasound transmission through the rectal wall into abdominal viscera. The probe is moved across the reproductive tract in a thorough and systemic manner (Ribadu et al, 1993).

ULTRASONOGRAPHY OF OVARIAN STRUCTURES

Ovarian Follicles and follicular waves: Ovarian follicles are fluid-filled structures surrounded by an inner layer of granulosa cells and an outer layer of thecal cells, which contain oocyte within the cavity of follicle called as antrum. Because fluid absorbs rather than reflects ultrasound waves, fluid-filled structures such as follicles appear as black circular structures (anechoic) surrounded by echogenic ovarian tissue. An ovarian follicle has a diameter greater than 2 to 3 mm and it can easily be tracked during serial scanning sessions (Pierson and Ginther, 1988). Due to noninvasive technique of ultrasonography, the follicular growth during the estrous cycle can be tracked by a series of examinations with out causing harm to the animals. Ovulation is characterized by the abrupt disappearance of the large ovulatory follicle (Eilts and Pechman, 1988). It can be detected by periodical examination of growing ovulatory follicle at two or three or four hours interval.
Corpora lutea: A CL can be identified by using ultrasonography from days 3 after ovulation. A developing CL appears on the ultrasound image as a poorly defined, irregular, grayish-black structure with echogenic spots all within the ovary; a mid-cycle CL is a well defined granular, grayish echogenic structure with a demarcation line visible between it and the ovarian stroma. In a regressing CL the demarcation line is faint, owing to the slight difference in echogenicity between the tissues (Pieterse et al, 1990). Corpora lutea with cavities appear as a centrally located nonechogenic area surrounded by grayish echogenic luteal structure. Ovarian Cysts: Rectal palpation of a large, fluid-filled structure is commonly used as a clinical indication of a follicular cyst. However, it is difficult to differentiate between follicular and luteal cysts via rectal palpation. Accuracy of diagnosis increases with the use of transrectal ultrasonography, which correctly diagnose luteal cysts in more than 90% of cases and follicular cysts by more than 75% of cases (Farin et al., 1992).
 

ULTRASONOGRAPHY OF UTERINE STRUCTURES

During the Estrous Cycle: The ultrasound image of the uterus showed a distinctly echogenic structure with different layers of the uterine horn reflected by differing echotextures. The echotexture of the endometrium is characterized by the presence of non-specular reflections with dark and bright signals seen within the ultrasound image of the endometrium (Pierson and Ginther, 1987). The ultrasonographic appearance of the uterus was influenced by the stage of the estrous cycle. Uterine echotexture was characteristically dark during the follicular phase (estrus) reflecting an extensive degree of edema of the endometrium. The uterine horns are curlier during luteal phase than during follicular phases.
During Pregnancy: The advantages of using ultrasonography for pregnancy diagnosis are that the early pregnancy can be conformed by ultrasonography, which is not possible by per rectal palpation, and that direct physical manipulation of the gravid reproductive tract is unnecessary with ultrasonography. Thus, the risk of inducing embryonic mortality is greatly reduced (Beal et al, 1992). Tentative early pregnancy diagnosis (before detection of the embryo proper) is based on the finding of discrete, nonechogenic structure or line within the uterine lumen which has to be confirmed by progressive elongation of the nonechogenic area and eventual detection of embryo proper. Generally, a 5 MHz or 7.5 MHz transducer tends to provide more reliable results than does a 3.0 MHz transducer for early pregnancy diagnosis. The level of accuracy depends on factors like; the type of ultrasound equipment used (sector or linear), transducer frequency (3.5, 5.0 or 7.5 MHz), stage of gestation and the experience of the operator (Boyd et al., 1988). Cows carrying twin pregnancies can be accurately identified using transrectal ultrasonography by 40 to 55 days post AI (Dobson et al., 1993). When conducting an early diagnosis for twins, the entire length of both uterine horns must be carefully scanned to ensure that an embryo is not missed. Since the majority of twinning in dairy cattle occurs due to double ovulations, the presence of two or more CL on the ovaries at the time of diagnosis can be an excellent indicator of cows with an increased risk of carrying twins. In general, ovarian indicators such as number and size of CL can enhance diagnosis of pregnancy status and twinning. The gender of fetuses can be detected by visualization of the location of the genital tubercle (Curran et al, 1989) or the scrotum and mammary glands (Muller and Wittowski, 1986). The most appropriate time of ultrasonographic sex determination is 55 to 60 days of gestation (Curran and Ginther, 1991).
Fetometry by Ultrasound: Estimation of fetal age, monitoring of fetal growth across time and diagnosis of pregnancy disorders can be performed by ultrasonographic fetometry. Growth curves of fetal structures based on ultrasonographic fetometry have been reported (Kahn, 1989). Pierson and Ginther (1987) reported that the embryonic vesicle gradually increased in length until day 26 when it started encroaching into the opposite horn. By day 32, the embryonic vesicle fully occupied both horns. The heart beat was visualized between days 26 and 29. Fluid filled structures (eyes, braincase, heart, and stomach) were most easily recognizable because of the nonechogenic nature of their contents. Intra-uterine development of the bovine fetus and its gestational age might be judged from the size of its organs and parts of the body. Ultrasonographic fetometry has been shown to provide a precise estimation of gestational age and prediction of calving dates. For close range visualization of the fetus, the 5 MHz transducer was used, while the 3.5 MHz transducer was preferred for viewing internal organs. Uterine involution completed at approximately 40 days based on ultrasonic assessment of uterine horn diameters (Santos et al., 1994).
Diagnosis of uterine affections: Different uterine affection is diagnose by using ultrasonography, includes endometritis, pyometra, fetal maceration and fetal mummification. Ultrasonographic appearance of endometritis and pyometra include varying degrees of distended uterine lumen filled with fluid of different consistency, which gives echogenic appears on screen (Fissore et al, 1986). Fetal maceration is diagnosed by appearance of echogenic fetal bones suspended in nonechogenic fetal fluids. Fetal mummification is diagnose by appearance of echogenic fetus in uterus without uterine fluid Ultrasonography may also be use to diagnose hydrometra and mucometra in cattle.
Evaluation of Artificial Insemination or Embryo Transfer Technique
Proper placement of semen or an embryo in the female tract is essential for achieving high pregnancy rates when cattle are bred by artificial insemination or embryo transfer. Transrectal ultrasonography can be used to identify the site of semen or embryo deposition. Correct placement of semen or an embryo is performed by using a metal bead which deposited semen or an embryo in the reproductive tract (Beal et al., 1989). The position and direction of the highly-echogenic bead is guided by ultrasonographic scanner. Ultrasound evaluation of the technique used by inseminators or embryo transfer technicians allows the correct deposition of semen or embryo.
 

ULTRASONOGRAPHY OF THE MALE REPRODUCTIVE SYSTEM

The evaluation of breeding bulls is based on semen parameters, scrotal circumference, and testicular palpation. Transcutaneous ultrasonic imaging has been used to characterize the ultrasonic morphology of the testicles of the bull (Eilts and Pechman 1988). Coulter and Bailey (1988) correlated the testicular dimension measured by ultrasound with testicular circumference, weight, and volume. The normal bull testicle has been reported to be homogeneous and moderately echogenic. The head and tail of the epididymis can be easily identified in all testes, but the epididymal body and vasdeferens were difficult to identify. Ultrasonic scanning of the bovine testicle was found to have no detrimental effect on reproductive capacity (semen characteristics, testicular dimensions and consistency) after exposure to a 3 minutes scan with a 5.0 MHz transducer (coulter and bailey, 1988). Transrectal ultrasonography is being use to measure the vesicular glands, ampullae and bulbourethral glands. Ultrasonography revealed testicular lesions in bulls (the changes observed included; increased glandular size, loss of normal lobular structure, increased glandular volume and the presence of bright fibrous tissue within the hyperechoic glandular parenchyma) and seminal vesiculitis.  

REFERENCES

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