2023 Southern WA sheep reproductive rates based on pregnancy scanning
Katherine Davies DPIRD Northam, WA; Andrew van Burgel DPIRD Albany, WA
Author correspondence: Katherine.Davies@dpird.wa.gov.au
The benefits of pregnancy scanning
Pregnancy scanning ewes for multiple foetuses has shown to be a valuable tool in sheep enterprises. In the October 2022 edition of Ovine Observer, John Young reported that utilising pregnancy scanning information and adopting optimum management resulted in an average 400% return on scanning investment across all flocks and times of lambing.
The dry season combined with reduced sheep prices this year mean that pregnancy scanning ewes will be an especially high value activity this season (Livestock Management 2023-2024). Pregnancy scanning allows producers to identify the poor performing or dry ewes and remove them from the flock, reducing the flock’s overall energy demand and conserving feed supplies for high performing stock.
Knowing the pregnancy status of ewes also means producers can implement different management strategies based on the number of foetuses a ewe carries. Highly productive, twin bearing ewes have a higher energy demand, and should have priority access to feed and the best lambing paddocks, aiming for condition score 3.2 at lambing to reduce ewe and lamb mortality. Single bearing ewes have a lower energy demand than twins, requiring less feed and should be managed for condition score 3 at lambing.
Our supplementary feeding calculator for pregnant and lactating ewes can help producers determine the amounts of feed required to meet these condition score targets based on the number of dry, single and twin bearing ewes in the flock.
Sheep pregnancy scanning benchmark tool
Pregnancy scanning data (anonymised) for Merino and meat breed ewes is collected by DPIRD annually from scanning providers across southern Western Australia (excludes any artificial insemination, embryo transfer and ewe lamb matings). DPIRD has just over 2.6 million individual ewe scanning records from 2015 to the current season, with over 1.7 million of those scanned for multiples.
The reproductive performance data is fed into our Pregnancy Scanning Benchmarks tool, which allows producers to compare their flock’s reproductive rate against other Merino or meat breed flocks in the Cereal Sheep Zone (CSZ) and the Medium Rainfall Zone (MRZ) with the same time of lambing.
The tool has now been updated with the latest pregnancy scanning data for multiples in 2023.
Pregnancy scanning data collected in 2023 stretches from Northampton in the north, through to Augusta-Margaret River, south to Albany and east to Ravensthorpe. Larger collections of pregnancy scanning data came from the shires of Williams, Kojonup, Dandaragan, and Cranbrook (Figure 1).
Conception and reproductive rates in 2023
Conception rate is the number of ewes scanned pregnant per 100 ewes joined and can be calculated when doing wet/dry scanning. Reproductive rate is the number of scanned foetuses per 100 ewes joined, therefore the number of foetuses per ewe is counted. This can also be called scanning for multiples or litter size. Reproductive rate reflects the potential lambing percentage, and as mentioned above, provides valuable information to optimise management.
Average conception and reproductive rates for 2023 were calculated by summing the number of ewes, dries, singles and twins across properties. This method gives equal weight to ewes (rather than properties) and therefore higher weight to larger flocks, as well as reducing the impact of outliers that typically occurred in smaller flocks.
The 2023 pregnancy scanning dataset included a total of 577,000 scanned ewes across 344 properties.
Non-merino (meat) breeds accounted for 86,000 of these scanned ewes across 60 properties, and had an average conception rate of 84%. For those properties that also scanned for multiples, the reproductive rate was 138%. Non-merino breeds were excluded from further statistical analysis between zones, time of scanning and years due to the smaller dataset.
The Merino conception rates outlined below are based on 491,000 ewes scanned across 284 properties. Of those, 287,000 Merino ewes across 148 properties were scanned for multiples and reproductive rates calculated.
The average Merino conception rate in 2023 was 89% with a reproductive rate of 134%.
The distribution of reproductive rates is summarised in Figure 2, with the highest proportion of Merino producers having reproductive rates between 120% and 150%.
Conception rates were higher for properties with large flocks (>1000 ewes) at 89% compared to 85% for smaller flocks (<1000 ewes) (p=0.040).
Conception rates were higher for producers that scanned for multiples compared to producers that only scanned for conception (89.4% vs 87.5%; p=0.010).
The reproductive rates between the CSZ and MRZ were not significantly different. The MRZ had more singles (48% vs 41%; p<0.001) with less dry ewes and twins as summarised in Table 1.
Table 1: Percentage of dry, single and twin for Merino ewes in the Cereal Sheep Zone (CSZ) and Medium Rainfall Zone (MRZ) in 2023 based on properties that scanned for multiples.
| Zone | Dry | Single | Twin |
| CSZ | 12% | 41% | 47% |
| MRZ | 9% | 48% | 43% |
Month of scanning
The time of scanning was earlier for the CSZ with 17% of ewes scanned by the end of February, compared to only 1% in the MRZ (Figure 3), indicating that the CSZ continues to have an overall earlier time of lambing than the MRZ.
Figures 4a and 4b below illustrate the differences in Merino conception and reproductive rate as the month of scanning progressed. January and June were omitted due to little data for these months. The variation in conception rates were not significantly different between months (Figure 4a). However, the reproductive rate (Figure 4b) increased significantly between scanning in February and March (125% to 140%; p=0.018) but then decreased to May (130%; p=0.025).
Results from previous years (2022, 2021, 2020) have shown that both conception and reproduction rates generally increase as the month of scanning progresses, which is to be expected in Merinos due to their natural breeding season. However, in 2023 there was a significant decrease in reproductive rate after March scanning.
Reproductive rate trend over years
The Merino ewe reproduction rate has varied depending on the season, with the pattern following the pattern in percentage of twins. The reproductive rate of 134% in 2023 was similar to the reproductive rate of 133% in 2022, and higher than the reproductive rates in 2020 (p=0.022) and 2021 (p=0.003) (Figure 5).
It’s likely given current seasonal conditions that average reproductive rates may decline in 2024, like they did for 2018 after the poor season in 2017. To maintain high reproductive rates going forward, producers must focus on ewe nutrition and condition score at joining, through pregnancy to lambing. Lifetime Wool data showed that for every increase of 1 condition score at joining, an extra 20 lambs are conceived (Figure 6).
In cases where feed is limited, supplementary feeding will be required to ensure ewes are in condition score 3 for joining. Work out a feed budget now, and ensure you start supplementary feeding early, before ewes start losing condition. It is much cheaper to maintain condition then it is to lose it and have to regain it for lambing.
After joining, pregnancy scanning results will allow producers to revisit their feed budgets, adjust accordingly and make decisions early on prioritising feed and lambing paddocks for highly productive stock.
Visit our Season 2023: Information for WA farmers webpage for further links to resources and calculators for feed budgeting and costing, supplementary feeding, condition scoring and confinement feeding.