Reaping the benefits of pregnancy scanning

With rams now in or soon to go in with the ewes, it’s time to book in your pregnancy scanner or consider pregnancy scanning if this is not yet a practice you’ve adopted. Pregnancy scanning for multiples is a critical management tool for optimum ewe and lamb survival, through differential feed allocation and other resources. Pregnancy scanning for multiples also enables you to understand where the biggest opportunity is to improve the reproductive performance of your flock – conception rate, scanning percentage or marking percentage. Poor conception rates (e.g. >15% empty ewes) when joining in the peak breeding season, i.e. January to April, require investigation to determine why ewes have failed to conceive, such as poor condition score, disease or weather. Lamb survival targets for Merinos are at least 90% for singles and 70% for twins. If your scanning and marking percentages differ significantly, this would indicate that improving lamb survival should be a priority to increase marking rate. 

The economics of pregnancy scanning

A benefit-cost analysis published by AWI and MLA in 2024 demonstrated that pregnancy scanning for multiples is, on average, twice as profitable as scanning for pregnancy status (pregnant or empty), at $5.55 per ewe versus $2.65 per ewe and representing a 400% return-on-investment. The analysis modelled two Western Australian locations, representing winter rainfall regions in Australia – Darkan and Cunderdin.

Pregnancy scanning for multiples was profitable across all regions, breeds and times of lambing included in the analysis. In the winter rainfall regions, the value of scanning was higher when lambing in autumn and slightly less if lambing in spring. This is because empty ewes in the earlier lambing flocks are identified before the main feed shortage, which increases the value of adjusting their nutritional management or from selling them after scanning. The lower value of scanning associated with later lambing does not equate to lower profit overall, as these flocks are often the most profitable because of the better match of pasture supply with the nutritional requirements of the ewes. 

Scanning for pregnancy status was not profitable in scenarios where scanning occurred after the main feed deficit, because the cost of pregnancy scanning and lower potential wool production exceeded the benefits associated with reproduction and feed allocation. The analysis suggested that scanning for pregnancy status is a good starting point for woolgrowers who are new to the practice but that the longer-term goal should be to scan for multiples.

Find results for all scenarios of the analysis here.

Optimising the accuracy of scanning

There are several ways that you can increase the efficiency of scanning and the accuracy of the scanning results. These include:

• Scanning at the optimal time – for a 5-week joining, it is recommended that scanning occurs 80-90 days after the rams go in for best accuracy. Your pregnancy scanner can help determine the optimal time of scanning for your enterprise. Make sure you book your scanner early i.e. when the rams go in!
• Ensuring adequate labour is available for mustering and keeping ewes up to the scanning crate. Up to 3000 ewes may be scanned in a day
• Ensuring ewes are free from vegetable matter, mud and other contaminants to allow the scanner to get good contact between the probe and skin. Poor contact can reduce the accuracy of scanning and slow the scanner down
• Ensuring your yards are in good condition and are set up to enable ewes to be drafted based on their pregnancy status
• Ensuring ewes are removed from feed and water for at least 6 hours before scanning, whilst provided with access to shade and shelter. Full rumens and bladders can reduce the accuracy of scanning

Turning the investment into profit

As with all data collected in sheep enterprises, pregnancy scanning results must be utilised to make management changes and selection decisions that improve productivity and profitability. Scanning to identify only the empty ewes restricts the options that can be implemented.

Removing passengers

Removing ‘passengers’, i.e. empty ewes, to increase the subsequent reproductive performance of the flock is the largest contributor to the profitability of pregnancy scanning, both for multiples and pregnancy status. Ewes may scan empty due to the impacts of management factors such as poor ewe and ram nutrition before joining. Such factors should be considered when deciding whether to sell or retain ewes that scan empty for the first time. Ensure that empty ewes are identified permanently. Ewes that scan empty twice should be removed from the breeding flock. 

In the analysis, selling once-empty ewes was optimal for flocks scanning just before the main feed deficit, providing that the weaning percentage is sufficient for the flock to be self-replacing, whereas selling twice-empty ewes was optimal for flocks scanning after the feed deficit or that are not self-replacing.

Optimising ewe nutrition

Ewe nutrition during pregnancy and lactation is a key determinant of the survival of the ewes and their lambs. After pregnancy scanning, empty ewes should be fed to meet maintenance requirements, with feed diverted to the pregnant ewes. Single- and multiple-bearing ewes should be managed differentially to meet their separate nutritional requirements, with feed prioritised for multiple-bearing ewes. Conduct regular feed budgets and monitor ewe condition score to ensure targets are being met between scanning and lambing. The target condition score for ewes at lambing is 3.0 for single-bearing ewes and 3.3 for twin-bearing ewes. In late pregnancy, i.e. the last six weeks before lambing, the energy requirements of single-bearing ewes are 40% higher and those of twin-bearing ewes are 76% higher than empty ewes. Peak lactation represents the period of greatest energy demand for breeding ewes and at this point, a twin-bearing ewe requires more than 5 MJ ME/day more than a single-bearing ewe. Hence the importance of scanning for multiples to optimise ewe nutrition! You can find the energy and protein requirements for ewes here.

Optimising paddock allocation

Multiple-bearing ewes should be allocated to paddocks with the best quality and quantity of feed between scanning and weaning, with mobs in poorer condition prioritised. Paddocks with the best shelter and that historically provide the best lamb survival results should be allocated to multiple-bearing ewes to optimise the survival of their lambs, which are on average born smaller and are more vulnerable to exposure than single-bearing lambs. Reducing the number of ewes in mobs at lambing also increases lamb survival, with the impact greater for multiple-born lambs. Hence, prioritise smaller mobs at lambing for multiple-bearing ewes. Subdivision of paddocks, for example using temporary electric fencing, can be used to achieve smaller mobs during lambing and improve the utilisation of shelter and pasture. Find more information on optimum mob size at lambing here.

Classing single- and multiple-born lambs separately

Single- and multiple-born lambs should be classed separately when making selection decisions due to the phenotypic disadvantages of multiple-born lambs (i.e. live weight/size, growth and wool quality). This will reduce the bias towards the selection of single-born progeny as replacements.

The value of the management changes

The average value of these management options, from the economic analysis described earlier in this article, are shown below.

Scanning for fetal age

Ewes may be scanned for fetal age (i.e. early or late) which enables pregnant ewes to be more precisely managed based on their expected time of lambing. For example, monitoring at lambing can focus on those mobs that are at peak lambing, nutrition can be better matched to requirements at the given stage of pregnancy, the time of lamb marking and weaning can be optimised, and paddock allocation can be improved.

This article utilises information from AWI and MLA’s recently released extension material on the value of pregnancy scanning to increase farm profitability and best-practice management before, at and following scanning. You can find more information, guides and a ewe management and pregnancy scanning checklist here.

Amy Lockwood, AWI Extension WA