Pregnancy testing in sheep relies on a handful of proven methods, each with its own window of reliability and trade-offs between speed, cost, and accuracy. Ultrasound scanning remains the most widely used and trusted approach on commercial farms, capable of confirming pregnancy and counting fetuses from roughly day 40 onward with accuracy above 99 percent. But blood-based tests detecting pregnancy-associated glycoproteins have closed the gap in recent years, offering a practical alternative that can flag pregnant ewes as early as three weeks after mating. Choosing the right test depends on flock size, how early you need the answer, and whether you also want to know how many lambs each ewe is carrying.
Why Testing Matters for Flock Management
Knowing which ewes are pregnant, and how far along they are, changes nearly every management decision from mid-gestation through lambing. Feeding a ewe carrying twins or triplets the same ration as a dry ewe wastes money on one end and risks starvation on the other. Ewes carrying multiple fetuses in late pregnancy are at particular risk of pregnancy toxaemia, a metabolic disorder sometimes called twin lamb disease, which develops when energy intake can’t keep up with the demands of rapidly growing fetuses.1In Practice. Advances in managing pregnancy toxaemia in sheep Sorting ewes into groups based on pregnancy status and fetal number lets you match nutrition to need, reduce metabolic disease, and avoid feeding expensive concentrates to animals that don’t need them.
Early pregnancy diagnosis also means you can identify barren ewes sooner. A ewe that didn’t conceive can be rebred in the same season, sold, or culled before you spend months feeding her for lambs that won’t arrive. On large operations running hundreds or thousands of ewes, that kind of sorting translates directly into profitability.
Ultrasound Scanning
Real-time ultrasound is the backbone of sheep pregnancy diagnosis worldwide. A technician places a probe against the ewe’s lower abdomen, just in front of the udder, and views the uterus on a portable screen. The whole process takes under a minute per animal once the operator is experienced. Using transrectal ultrasound, pregnancy can be detected between 20 and 28 days after mating, though transabdominal scanning, which is faster and less invasive, becomes reliable a bit later.2PubMed Central. Ultrasound parameters of early pregnancy and Doppler indices of blood vessels in the placenta and umbilical cord throughout the pregnancy period in sheep
The real strength of ultrasound is that it can do two things at once: confirm pregnancy and count fetuses. Between days 50 and 100 of gestation, experienced operators achieve pregnancy diagnosis accuracy above 99 percent and can differentiate between singles, twins, and triplets at rates around 97 to 98 percent.3PubMed. Real-time ultrasonic scanning in the diagnosis of pregnancy and the determination of fetal numbers in sheep Earlier in gestation, around days 29 to 39, the pregnancy-or-not call is still extremely reliable, but fetal counting is trickier because the embryos are small and can overlap on the screen.4PubMed. Accuracy of pregnancy diagnosis and prediction of foetal numbers in sheep with linear-array real-time ultrasound scanning One study found that the handful of apparent false positives at early scanning were likely caused by embryonic loss or undetected abortions that occurred after the scan, not by errors in the ultrasound itself.
Fetal counting accuracy does vary with operator skill. In the same trial, an experienced scanner achieved 95 to 100 percent accuracy across categories, while a less experienced operator ranged from 90 to 97 percent.5PubMed. Real-time ultrasonic scanning in the diagnosis of pregnancy and the determination of fetal numbers in sheep That gap matters on commercial farms, where the whole point of scanning is to separate singles from multiples for differential feeding. If twins get sorted into the singles group, you’re back to the under-nutrition problem you were trying to solve.
Cost and logistics are the main downsides. You need a trained technician with portable equipment who can move through the flock efficiently. In remote pastoral operations, getting a scanner to the sheep can be a challenge in itself. Still, most commercial flocks in countries with well-developed sheep industries treat ultrasound scanning as a routine annual event, scheduled around 80 to 90 days of gestation for the best combination of pregnancy confirmation and fetal counting.
Blood Tests for Pregnancy-Associated Glycoproteins
Pregnancy-associated glycoproteins, or PAGs, are proteins produced by the placenta. They appear in the ewe’s bloodstream within the first few weeks of pregnancy and rise steadily, making them a useful target for blood-based pregnancy tests. The appeal is straightforward: collect a blood sample, send it to a lab (or run a rapid test on-farm), and get a pregnant-or-not answer without needing an ultrasound machine or a skilled scanner.
In a radioimmunoassay study, PAG testing at day 22 after artificial insemination achieved about 94 percent sensitivity and 100 percent specificity, meaning it almost never called a non-pregnant ewe pregnant.6Theriogenology. Early pregnancy diagnosis in sheep by progesterone and pregnancy-associated glycoprotein tests A more recent field evaluation of a commercial lateral flow assay, essentially a rapid strip test, showed that accuracy improved with gestational age. At 21 days after mating, sensitivity was about 78 percent, but by day 28 it climbed to around 96 percent, and by day 35 it hit 100 percent sensitivity with about 96 percent specificity.7PubMed. The field evaluation of the diagnostic performance of a commercial pregnancy-associated glycoprotein-based lateral flow assay for early pregnancy detection in ewes The researchers concluded that the test is practical and reliable from day 28 onward.
A visual ELISA format designed for on-farm or small-lab use has also been validated, showing 100 percent sensitivity and about 94 percent specificity from day 30 of gestation. Samples at 28 days were sometimes harder to interpret visually, so 30 days was recommended as the earliest practical time point for that particular test format.8PubMed. Visual ELISA for detection of pregnancy-associated glycoproteins (PAGs) in ewe serum An on-site pregnancy test called Pregnostx, evaluated side by side with ultrasound, achieved about 97 percent sensitivity overall, with perfect agreement at 25 to 35 days of pregnancy.9World Journal of Advanced Research and Reviews. Comparative evaluation of pregnancy diagnosis in sheep using On-site pregnancy test (Pregnostx) and ultrasonography
The main limitation of PAG tests is that they tell you pregnant or not pregnant, period. They do not count fetuses. If your primary goal is to sort ewes by litter size for nutritional management, you still need ultrasound. But if you just want to cull or rebreed empty ewes quickly, a PAG blood test at four weeks post-mating is a fast and increasingly affordable option.
Progesterone Testing
Progesterone is the hormone that maintains pregnancy in most mammals, including sheep. A high progesterone level around 18 days after breeding suggests the ewe has not returned to estrus and is likely pregnant. In one study, progesterone testing at day 18 achieved 100 percent sensitivity, catching every pregnant ewe, but specificity was only about 95 percent, meaning some non-pregnant ewes were incorrectly flagged as pregnant.10Theriogenology. Early pregnancy diagnosis in sheep by progesterone and pregnancy-associated glycoprotein tests That happens because a non-pregnant ewe with a persistent corpus luteum or irregular cycling can still have elevated progesterone without actually carrying a lamb.
Progesterone testing is better at telling you which ewes are definitely not pregnant than confirming which ones are. A low progesterone level at day 18 essentially rules out pregnancy. A high level means “probably pregnant, but confirm later.” This makes progesterone most useful as a quick screen: pull the low-progesterone ewes out for rebreeding and schedule ultrasound or PAG confirmation for the rest.
On the practical side, one interesting development is the validation of human progesterone ELISA kits for use with sheep plasma. Researchers found that a commercial kit designed for human clinical labs worked reliably for ovine samples, with repeatability and accuracy meeting international method-validation standards.11PubMed Central. Measurement of progesterone in sheep using a commercial ELISA kit for human plasma This matters for veterinary clinics in regions where species-specific kits are expensive or hard to source.
Chute-Side and Rapid Field Tests
The holy grail for sheep producers, especially those running range flocks in remote areas, is a test you can run chute-side without sending samples to a lab. Several companies have developed rapid tests designed for this purpose, and the results are mixed depending on when you use them.
An evaluation of the IDEXX chute-side pregnancy test in Rambouillet ewes showed that accuracy was modest at day 20 of gestation, roughly 35 to 54 percent depending on the sample type. By day 35, accuracy was still only around 61 percent. But at day 70, the test agreed with later progesterone-confirmed pregnancy status about 91 to 93 percent of the time, approaching the reliability of established methods.12PubMed Central. Efficacy of a chute-side pregnancy test on early pregnancy determination in mature Rambouillet ewes The take-home message is that these rapid tests can work well, but the timing window matters enormously. Using them too early produces results that are barely better than flipping a coin.
Research into blood metabolite panels has identified a set of five compounds, including glucose, urea, and carnitine, that can distinguish pregnant from non-pregnant ewes with reasonable accuracy by day 50 and very high accuracy by day 70.13Scientific Reports. Predictive blood biomarkers of sheep pregnancy and litter size These metabolomic approaches are still more research-grade than farm-ready, but they point toward a future where a single blood draw could confirm pregnancy and perhaps estimate litter size through biomarker profiles.
Physical Examination Methods
Before ultrasound and blood tests became widely available, producers relied on hands-on methods. Abdominal palpation, essentially pressing on the ewe’s belly to feel for a fetus, is the simplest and cheapest approach. In Merino ewes between 90 and 130 days pregnant, abdominal palpation was 80 to 95 percent accurate, with accuracy improving as the pregnancy advanced and the fetus grew larger and easier to feel.14PubMed. The diagnosis of pregnancy in sheep by abdominal palpation The technique requires no equipment at all, just a practitioner with experience. Its obvious limitation is that it only works in later pregnancy when the fetus is large enough to detect through the abdominal wall.
A more systematic technique is rectal-abdominal palpation, where a smooth plastic rod is inserted into the rectum to press the uterus against the abdominal wall, allowing the operator to feel for fetal structures. This method can detect pregnancy as early as 43 days after breeding and approaches near-perfect accuracy by 65 to 70 days. Proponents claim throughput of 200 or more ewes per hour.15Journal of Animal Science. A Rectal-Abdominal Palpation Technique for Diagnosing Pregnancy in the Ewe In a large-scale trial of over 1,800 ewes across three flocks, correct diagnosis was achieved in 97 percent of cases with no evidence of ewe mortality or abortion, and throughput exceeded 120 ewes per hour.16PubMed. Pregnancy diagnosis in sheep using a rectal probe
However, the technique carries a real risk of injury. Subsequent research found that rectal perforations occurred in anywhere from 1 to 18 percent of ewes examined, depending on the experiment and conditions. Bruising or abrasions of the rectal wall were even more common, appearing in 18 to 46 percent of ewes. Non-pregnant ewes were at least twice as likely to sustain rectal damage as pregnant ones, possibly because the empty uterus is harder to locate, requiring more manipulation.17Journal of Animal Science. Rectal Damage in Ewes following Pregnancy Diagnosis by Rectal-Abdominal Palpation These injury rates largely explain why the method has been superseded by ultrasound and blood testing in modern practice.
Older Ultrasonic Devices
Before real-time imaging scanners became portable and affordable, simpler Doppler instruments were used to detect fetal heartbeat or arterial pulse through the abdominal wall. These devices did not produce an image; they converted motion into audible sound. In ewes between 75 and 92 days pregnant, diagnostic accuracy with Doppler instruments reached about 99 percent.18Journal of Animal Science. Pregnancy Diagnosis in the Ewe Using an Ultrasonic Doppler Instrument An Australian comparison of six pregnancy diagnosis methods found that dedicated A-mode scanners like the Scanopreg and Pregmatic devices achieved 96 to 98 percent accuracy in pregnant ewes after 50 days, though accuracy in non-pregnant ewes was somewhat lower, around 87 to 96 percent.19Australian Veterinary Journal. A comparison of six methods used for detecting pregnancy in sheep
These older instruments were cheaper and simpler than modern real-time scanners, and some are still used in developing regions. Their main weakness is that they cannot count fetuses, only detect whether something alive is in the uterus. Given that fetal counting is one of the biggest practical reasons to scan, most operations that invest in ultrasound equipment now opt for real-time B-mode scanners that provide an actual image.
Determining Fetal Sex
For most commercial flocks, knowing pregnant-or-not and how many is enough. But in some breeding programs, particularly those involving embryo transfer or expensive genetics, knowing the sex of the fetus before birth has real value. Ultrasound can accomplish this by locating the genital tubercle, a small anatomical landmark that migrates to different positions in male versus female fetuses.
In naturally mated ewes, fetal sex determination by ultrasound became possible from day 50 onward, with one study reporting 100 percent accuracy.20Journal of Reproduction and Development. Ultrasonographic Fetal Sex Identification in Pregnant Sheep Derived from Natural Mating and Embryo Transfer In embryo transfer pregnancies, the window opened slightly later, around day 55. Another study using transrectal ultrasound at 60 to 69 days post-breeding achieved 89 percent total accuracy, with males correctly identified 100 percent of the time and females at 76 percent, plus a small percentage of fetuses where sex could not be determined at all.21PubMed. Fetal sex determination by ultrasonically locating the genital tubercle in ewes The pattern across studies is consistent: male fetuses are easier to sex correctly because the genital tubercle migrates further from its starting position in males, making it more distinct on the screen.
A completely different approach uses cell-free fetal DNA circulating in the mother’s blood. By testing for the SRY gene, which is carried only on the Y chromosome, researchers correctly identified all male pregnancies with no false positives or false negatives across 46 ewes from the second through fifth month of gestation.22PubMed. Detection and quantification of cell-free fetal DNA in ovine maternal plasma; use it to predict fetal sex A follow-up investigation tested whether the same gene could be detected in cervical mucus as well as blood plasma. The blood-based test was slightly more reliable, successfully identifying 12 out of 15 male-bearing ewes versus 11 out of 15 from cervical mucus.23Asian Pacific Journal of Reproduction. Ovine fetal sex determination using circulating cell-free fetal DNA (ccffDNA) and cervical mucous secretions This DNA-based sexing is currently a research tool rather than a routine farm practice, but the concept mirrors the non-invasive prenatal testing already in widespread use in human medicine.
Matching the Test to Your Situation
The best pregnancy test for a given flock depends on what you need to know and when. Here’s how the practical trade-offs shake out:
- Earliest answer: A progesterone test can indicate likely pregnancy as soon as 18 days after mating, though it works better as a rule-out than a confirmation. PAG blood tests become reliable around day 28 to 30.
- Pregnancy plus fetal count: Real-time ultrasound between days 50 and 100 is the only method that reliably delivers both pieces of information in a single pass.
- Lowest cost, no equipment: Abdominal palpation costs nothing but time and experience, though you have to wait until at least 90 days of gestation.
- Remote or low-resource settings: Rapid lateral flow PAG tests and chute-side kits are improving in accuracy and may eventually replace the need for ultrasound technician visits, especially where fetal counting is not the priority.
- Fetal sexing: Ultrasound from day 50 onward in the hands of a skilled operator, or cell-free fetal DNA testing from a blood sample if laboratory access is available.
Timing is the thread that runs through all of these options. Every method has a window during which it performs well and a window during which it doesn’t. Testing too early with any method produces unreliable results, wastes money, and can lead to wrong management decisions. A PAG lateral flow test at 21 days might miss one in five pregnancies; the same test two weeks later catches virtually all of them. A Doppler device at 56 days of gestation is less reliable than the same device at 80 days. Building your testing schedule around the validated accuracy windows of your chosen method is more important than picking the fanciest technology available.
False Results and What Drives Them
False negatives, where a pregnant ewe tests as open, are generally more common than false positives across all methods. With ultrasound, they happen most often in very early scans or with inexperienced operators. With PAG blood tests, the main cause is testing before placental PAG production reaches detectable levels. Either way, the fix is the same: retest animals that scanned open if you suspect the timing was borderline.
False positives are trickier because they have multiple causes. In progesterone testing, ewes with persistent corpora lutea will show high progesterone without being pregnant. In ultrasound scanning, a ewe may genuinely be pregnant at the time of the scan but lose the pregnancy afterward through embryonic death or unobserved abortion, making the test appear “wrong” when lambing records are compared later. One scanning study specifically noted that its three apparent false positives were likely explained by fetal mortality after the exam rather than operator error.24PubMed. Accuracy of pregnancy diagnosis and prediction of foetal numbers in sheep with linear-array real-time ultrasound scanning This distinction matters: the scan was correct at the time, but the pregnancy didn’t survive to lambing. Producers who understand this are less likely to lose confidence in their testing program over a handful of ewes that scan pregnant but lamb dry.
Body condition can also affect test accuracy. Overly fat ewes are harder to scan transabdominally because the layer of internal fat degrades the ultrasound image. Heavily woolled ewes scanned without adequate fleece parting can produce poor images for the same reason. Preparing ewes properly, including withholding feed for 12 to 24 hours before scanning to reduce rumen fill, improves image quality and speeds throughput.