Should You Pregnancy Scan Your Ewes?

Pregnancy testing in ewes is performed via trans-abdominal ultrasound. The ideal time for this procedure is from 45 days of gestation (7 weeks after rams out). Scanning for empty / pregnant or for multiple pregnancy can be performed and a report and interpretation of results should be provided. Pregnancy testing can also be used as one part of an investigation of poor reproduction performance in a flock.

The decision to pregnancy scan ewes, either for empty/pregnant or multiples, is an important one. The economic benefit of pregnancy scanning is greater in situations where there are more dry ewes in the mob, where there are more twin-bearing ewes in the mob, and in poor seasons where a feed shortage and/or high feeding costs have been predicted. 

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Several economic models of the value of pregnancy scanning have shown variable results depending on a number of factors. If you have any of the following in your mobs, scanning may not provide a return on investment:

• If dry ewes are 5% or less
• No value in scanning for multiples if twin rates are under 15%
• No value in scanning for multiples in a merino or crossbred flock if dry ewes are less than 10%

Modelling by Holmes and Sackett in 2008 suggested that it was more profitable to feed the entire ewe flock as if they were single-bearing and due to lamb in the first cycle, rather than scanning and managing according to pregnancy status. The value of lambs now is significantly higher than 2008 but so is the cost of supplementary feed, so this recommendation may still have some merit.

If you lamb at a time of the year where you are confident you can provide 1200kgs or more of green Feed on Offer in lambing paddocks, scanning is of little economic benefit. The cost of scanning itself has a minor effect of the return on investment for scanning and therefore should have an equally minor influence on the decision to scan for pregnancy status. An economic benefit from scanning will only be realised when management changes as a result of scanning are implemented, such as feeding multiple bearing ewes appropriately.

The following benefits may be realised:
Immediate Benefits

• Sale of dry ewes to minimise feeding
• Fewer deaths of pregnant ewes in late pregnancy or lactation
• Improved lamb survival especially in multiple births
• Keeping dry ewes but running as wethers with lower feed input and greater pasture utilisation
• Paternity identification for AI or ET programs
• Improved wool quality in:
  • Twin-bearing ewes
  • Maiden ewes
  • The progeny of twin-bearing and maiden ewes

Benefits the year following scanning

• Improved wool quality in hoggets
• Greater numbers of hoggets from which to choose replacements or sell
• Fewer twin-rearing ewes are dry the following season
• Improved fecundity in twin-rearing ewes the following season
  • Over 60% that were twin-bearing will twin again the following year. If not scanned and fed appropriately, only 32% of twin-bearing ewes will twin again the following year

Lifetime Benefits

• Improved wool quality in the progeny of twin-bearing and maiden ewes for their lifetime (heavier fleeces, finer fibre diameter)
• Fewer incidences of “micron blowout” in scanned flocks where scanning if practiced every year

The loss rate of scanned embryos between scanning and birth can be significant.  A number of Australian studies have quantified this loss rate at around 12% of embryos scanned. The Kangaroo Island Veterinary Clinic team provide a full sheep scanning and poor reproduction investigation service. To book your ewe scanning, please ring 8553 2485.