Sheep Pregnancy Scanning: The Day 45-90 Ultrasound Window

Scanning is the highest-return hour of the sheep year. For a modest cost per ewe, you learn who is pregnant, who is empty, and, critically, how many lambs each ewe is carrying. Everything downstream gets better: feeding, shed planning, staffing, culling. A flock that is fed as one group is a flock where the singles are fat and the triplets are starving.

Why days 45-90

Transabdominal ultrasound in sheep works across a broad range of gestation, but the practical window is day 45 to day 90 after service, and the reason is a trade-off.

Too early (before ~day 40):

• Fetuses are small and hard to resolve.
• Pregnancy can be detected from around day 30-35, but fetal counting is unreliable.
• Early embryonic loss may not yet have shown up, so you can record a pregnancy that does not persist.

Too late (after ~day 90):

• Fetuses drop deeper into the abdomen and become harder to image cleanly.
• They start overlapping each other, so a triplet gets miscounted as a twin.
• You have lost the run-up you need to act on the results, the late-gestation feeding plan should already be starting.

Between 45 and 90 days, the fetuses are large enough to see clearly and still separated enough to count. Many operators favour the tighter day 60-80 band as the accuracy sweet spot.

Days after service	What you get	Verdict
30-40	Pregnant / not pregnant, low confidence	Too early to count
45-60	Reliable pregnancy diagnosis, good counting	Good
60-80	Best counting accuracy	Ideal
80-90	Still workable, counting slips	Acceptable
90+	Pregnancy yes, counts unreliable	Too late to be useful

The Sheep Gestation Calculator will show you when this window opens and closes for your tupping date, so you can book the scanner for the right fortnight rather than guessing.

Timing a scan across a whole flock

Here is the wrinkle: your ewes were not all served on the same day. If your rams were in for a full 34-day period (two cycles), your ewes span 34 days of gestation on any given date.

The fix is to book your scan date relative to the middle of the mating period. Aim so that:

• The earliest-served ewes are no more than ~90 days pregnant.
• The latest-served ewes are at least ~45 days pregnant.

A scan around day 75-80 from the start of tupping usually catches everybody inside the usable window. If your mating period was long, six weeks or more, accept that the tail-end ewes will be scanned early and their counts will be less reliable.

What accuracy to expect

With a competent operator and a decent machine:

• Pregnant vs. empty: very high accuracy, typically well above 95%.
• Singles vs. multiples: high accuracy.
• Triplets vs. twins: this is where errors live. A triplet miscounted as a twin is the most common scanning error, and it is the one that costs you, because that ewe gets underfed.

A practical hedge: treat any ewe scanned as twins but carrying poorly, or any ewe in a high-prolificacy group, as a potential triplet at feeding time. Feeding a twin-bearing ewe as if she might be a triplet costs a little feed. Underfeeding a genuine triplet costs you lambs.

Preparing ewes for scanning

The operator’s job is much easier, and your results much better, if you do this:

• Hold ewes off feed for roughly 12 hours beforehand. A rumen packed with forage pushes the uterus out of position and obscures the image. Water should remain available.
• Keep them calm. Stressed ewes moving through the race quickly get scanned quickly and badly.
• Set up a good race and a clean, sheltered flow. The operator needs shade, bright sunlight on a screen is the enemy of accurate counting.
• Have a marking system ready. Stock marker spray, one colour per result, applied on the spot.
• Have three pens on the exit, empty, single, multiple, and draft as you go. Do not plan to sort them out later.

Using the results

This is the part people underdeliver on. The scan is worthless if you feed everybody the same afterwards.

Empty ewes

Decide in advance what happens to them. Culling barren ewes is the usual answer, but check first for a systemic cause, if 15% of the flock is empty, suspect the ram (fertility, lameness, injury), tupping management or ewe body condition, not the individual ewes.

Singles

Risk of over-conditioning. Fat ewes have harder lambings and bigger, sometimes oversized single lambs. Keep them on a maintenance plane and do not fold them in with the triplets.

Twins

The main body of the flock. Standard late-gestation step-up.

Triplets (and more)

The group that needs everything: highest energy and protein density, most space, closest watching. They also tend to lamb earliest, multiples typically arrive one to two days before singles, so they should be the first group in the shed.

A useful downstream effect

Scanning also sharpens your lambing dates. A ewe scanned as carrying triplets is likely to lamb toward the earlier end of the 142-152 day window; a single-bearing ewe toward the later end. Combine that with your service date and you get a materially better estimate of when the shed gets busy.

Cost, and whether it is worth it

Scanning is typically charged per head and is one of the cheapest interventions in the sheep calendar. The return comes from three places:

• Feed saved on empty ewes and singles.
• Lambs saved in triplet-bearing ewes that would otherwise have been underfed.
• Culling decisions made in autumn rather than discovered in spring.

For any flock above a handful of ewes, it pays for itself. For smallholders with ten ewes, it is a harder sum, but even then, knowing who is empty before you feed them all winter is worth something.

This article is general husbandry guidance, not veterinary advice. Discuss scanning timing and interpretation with your vet or scanning operator.

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Plan your lambing dates: use the free Sheep Gestation Calculator to turn a breeding date into an expected lambing date, a 142–152 day window and a full milestone timeline. Estimates only, always consult a veterinarian for animal-health decisions.

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