Ultrasound, as a diagnostic tool in Equine management and health care, has become staple of our industry. While the Racing and Show World utilizes ultrasound to scope everything from lungs to limbs, it is the reproductive aspects we will address here.
Ultrasound technologies and their use have been with us since the late 1950s. Given it’s recognized benefits and efficacy for medical diagnosis, it is also one of the clinically safest procedures available for both technician and patient.
Let us begin with how ultrasound works. The machine itself, by way of a transducer sends out beams of sound for very short periods of time, and then listens for echos. Perhaps the best example would be; Place yourself in a large, empty room. You shout and then listen. An echo is heard as sound bounces off the walls. The further away you stand from the wall, the longer it takes for the echo to return to you. You have now sent out a sound beam, and your ears are picking up the returned echo. Your brain translates this into a picture, or recognition.
The ultrasound machine is simulating this by using what it hears, to create a picture on a screen. Every time it hears an echo from the sound beam it has sent out, translates it onto a monitor. The location of each dot depends on how long it takes the echo to reach the machine. Gray shades are determined by how strong, or loud, the machine perceives the echo to be. An echo from a hard smooth surface will be louder then a soft bumpy surface. A strong echo comes from deeper, and is perceived and viewed as a whiter image. While a weak or soft echo, being either closer proximity or fluid, will be grey to black. The ultrasound machine sends out thousands of beams a minute in order to create the image we see on the screen. It then takes a trained technician, (vet) to read the images.
Tissues vary in their echocentricity, or ability to reflect sound waves. Air and dense tissue reflect most sound waves, whereas fluids propagate them. Reflected sound waves are received by the transducer and converted to electronic impulses in the machine, and displayed on the monitor.
The equipment consists of these three primary parts:
- The TRANSDUCER is the component held in the examining hand of the person performing the ultrasound. Within it is a crystal that emits the ultrasonic beam, or high frequency sound wave, and then “listens” for the echoes. The echoes produce images of soft tissues and organs. The examiner moves the transducer within the area to be examined, aiming it at specific structures such as the ovaries or uterus.
- The MONITOR is simply a TV screen that receives and displays the images created. Often it has a stop / freeze capacity, and an attached Polaroid camera for capturing the images.
- The MACHINE contains the computer and power to transform the echoes the trasducer hears, to the picture you and the examiner see on the monitor. It also has a control panel and can measure structures, such as follicles.
There are currently two methods of performing reproductive ultrasounds, trans- abdominal and trans-vaginal.
The trans-abdominal method is frowned upon in equines, due to the density of the body, and conflicting organs. There are commercially available units, used by breeders to identify early pregnancies. These do not have capability or accuracy in pregnancies past 14 days, and do not detect ovulation or additional reproductive applications.
Trans-vaginal ultrasound is the form breeders are familiar with. After carefully removing feces from the rectal tract, an ordinary rectal palpation is done. Next, a well lubricated transducer is introduced into the rectum of the mare, and as with palpation, the organs are identified and scanned, in a systematic manner. Care is taken that no air or fecal matter is caught between the transducer and the tissue or organ of interest. It is also preferable to advance the transducer over the cervix and body of the uterus until the bifurcation of the uterus is visualized. The transducer is then moved slowly over the horn to the tip, to image the ovary. Pre-ovulatory follicles are seen as black spheres, as they are an-echoic, or fluid filled. Ovulating follicles have a pear shape or are losing their cylindrical shape. Post ovulation, the follicle becomes a corpus luteum, or yellow body, losing it’s fluid content, and are viewed as a light grey or white sphere.
Diagnostic ultrasonography is used in the broodmare for:
- Evaluation of ovarian activity; Gauging stages of estrus cycle, identifying estrus, diestrus, anestrus, prediction of ovulation, “silent heat” mares.
- Detection and evaluation of pregnancy; With a high quality ultrasound unit, equipped with a 5 MHz trans-rectal transducer, embryonic vesicles can be detected as early as 9-10 days post ovulation, also twins, and estimation of conceptus age. Additionally, gender can also be determined, by identifying the position of the genital tubercle, at 60 to 70 days post ovulation.
- Diagnosis of changes and problems in the reproductive tract; These can include, but are not limited to, uterine endometrial cysts, fluid accumulations, abscesses and masses.
Although not a common procedure, ultrasonography in the stallion is a excellent tool for diagnostics of what otherwise would be inaccessible. It permits non invasive evaluation of the testes. This would be for both fertility problems and to estimate daily sperm output. Rectally in the stallion, it allows access to the accessory genital glands, and abdominal / inguinal exploration for chryptorchids.
In the growing field of Frozen Semen, success greatly hinges on the use of ultrasound. Frozen spermatazoa, post thaw, have a very short life span. Unlike fresh chilled or live cover, whom can have a 48 hour viability post ejaculation, thawed cell have a 6 to 8 hour viability. Thus timing the insemination, 8 hours prior, or 6 hours post ovulation, must be strictly adhered to. Ultrasound checks are numerous when ovulation approaches, and can admittedly be quite costly. Additionally, since there is a higher occurrence of uterine inflammatory response with frozen semen, one must check to make certain the uterus has evacuated efficiently. Often this is with the aid of Oxytocin and post insemination flushes. Uterine fluid will show up as black, since they are an-echoic, in an ultrasound exam.
There will repeatedly be the controversy of cost versus chance, in taking advantage of the ultrasound technology. I seem to always have the same response. Horse shows are very costly, as are trainers, advertising. trucks, trailers, show clothes, barns, stud fees, shipping, feed, and on and on. Why start short changing now. Success in a breeding program is money saved. Foals on the ground, with the least amount of effort, makes for a monitarily successful, and professional, breeding business. Certainly not all breeding endeavors require ultrasound. Yet, please consider, it can be one of the most time, labor, and overall cost saving tools you can employ.
Many thanks to Dr. Bob Smith, of Palm West Veterinary Hospital, Wellington Florida, for his patience, photos, and ultrasound information and expertise. Also, thanks to Lassergut Farms, USA for sharing their experience and use of their mares and facility.