The two most reliable methods for pregnancy status in small ruminants are ultrasound and the detection of pregnancy-associated glycoproteins (PAG) by blood pregnancy tests. We more commonly use a veterinary ultrasound machine for pregnancy testing, which gives faster (real-time display of test results) and more comprehensive information (can measure litter size, fetal development, dead or alive fetuses, etc.).
Ultrasound is a common method of pregnancy diagnosis in small ruminant sheep and goats and can be performed transabdominally or transrectally using a portable veterinary ultrasound machine. Devices with linear, variable frequency transducers (frequency range 5-7.5 MHz) are commonly used for cattle breeding herd management and can also be used for pregnancy diagnosis in small ruminants. When performing transrectal ultrasound on small ruminants, a probe extender can be used, but the operator should ensure that the animal is well restrained and that the procedure is performed carefully to avoid injury to the rectal mucosa.
In addition to confirming pregnancy status, the use of ultrasound provides additional benefits to the clinician. Ultrasound allows for a more accurate estimation of days of gestation, thus enabling producers to group ewes or ewes according to their due date. In addition, the determination of fetal counts assists in the nutritional management of ewes or multiparous ewes to prevent perinatal pregnancy toxemia. The use of ultrasound to determine fetal males and females may also be valuable for stock management in herds or flocks. Finally, ultrasound can determine fetal viability and detect any uterine pathology that may be detrimental to the reproductive health of the ewe.
In small ruminants, anechoic fluid in the uterine cavity can be detected as early as 17-19 days of gestation by transrectal ultrasound or 25-28 days by transabdominal ultrasound. Fluid in the uterine cavity should not be the sole basis for confirmation of pregnancy, but should be used in conjunction with identification of the amniotic sac and fetal heartbeat for definitive diagnosis. The fetal heartbeat can be detected as early as 16 days’ gestation in ewes and 22-23 days’ gestation in does using the transrectal method. When scanned by the transabdominal method, fetal heartbeats could be reliably detected in both ewes and at 27-30 days of gestation.
Determination of fetal number in small ruminants may be an important aspect of pregnancy diagnosis. Knowledge of fetal number allows producers to adjust nutritional management to prevent pregnancy toxemia in these litter-bearing species. The gold standard for determining fetal number is by ultrasound. Fetal counts can be determined with greater than 80% accuracy if performed between approximately 30-70 days of gestation. After 70 days of gestation, it may be difficult to distinguish multiples because of the increase in fetal mass. A good rule of thumb to maintain accuracy in the diagnosis of multiple fetuses is to perform a count only when more than one fetus can be visualized in the same field of view by ultrasound. Ultimately, the determination of the number of fetuses increases the time required to examine the ewe and the value of that information depends on how the client uses the information provided by the veterinarian. If management changes are not made based on the number of fetuses, it may not be worth the extra time spent counting fetuses during pregnancy diagnosis.
Pregnancy diagnosis in small ruminant herds and sheep flocks is key to maintaining farm profitability. Determination of gestational status, gestational age and number of fetuses gives veterinarians the opportunity to help their clients provide a high level of care and nutritional management during pregnancy and the perinatal period.
Post time: Aug-15-2024