Successful pregnancy scanning
The commercial availability of ultrasound scanning for pregnancy in ewes has been a major development for the sheep industry. It enables farmers to know the pregnancy status of their ewes about two months before they are expected to start lambing.
Efficient & accurate scanning needs:
• Length of joining to be 5 weeks and no more than 6 weeks.
• Tease ewes where joining starts before mid January.
• Keep rams out of flocks at other times.
• Stop supplements one or two days before scanning is to be done.
• Take ewes off feed and water the night before scanning.
• Ensure enough help is available on the day of scanning to keep the ewes moving.
• Good yards and panels to allow subdivision of the scanned ewes.
When do I scan?
Using an ultrasound machine, uterine fluid can be detected in ewes from day 55 of pregnancy. By day 70 after joining, pregnancy and the number of foetuses can be detected with a high level of accuracy. This degree of accuracy is maintained between days 70 and 100. While ewes with foetuses older than 100 days can still be pregnancy scanned, shading caused by bones developing make it difficult to determine the number of foetuses present.
Figure 1. The optimum time for pregnancy scanning.
How do I prepare for scanning?
In order for scanners to accurately determine pregnancy status it is important for the ewes to be presented to them at the optimum time. This is particularly important for the detection of multiple pregnancies.
The optimum joining period is 5 weeks and no longer than 6 weeks. This length of joining allows two chances for the ewes to conceive where they are all cycling. If joining occurs before mid January, it is important to effectively tease ewes (with testosterone treated wethers or vasectomised rams) to ensure that all the ewes are coming into oestrus and can conceive successfully. Because of the need for a relatively short period for conception, it is important that stray rams not get with the ewes at other times. The longer the joining period, the more difficult it is for scanners to give accurate results.
Before the scanner arrives
The ewes should be taken off feed and water the night before they are to be scanned. The ewes also should not be given any supplements (eg. grain, hay and silage) during the day before scanning.
It is important that scanners can set up their gear in good yards that have been watered down to reduce dust while scanning. Also, it is important that scanners have enough help to allow for the efficient movement of the ewes so that they flow well through the yards and aren’t squashed entering the scanners area. The ewes should be able to be drafted promptly if they need to be split on pregnancy status and be tagged/ marked to reflect their pregnancy status. Setting up a
drafting gate at the exit of the scanning crate is a good option. Portable or temporary yards will need to be set up to handle this or at least there be labour available to mark ewes for drafting later.
Should I scan for multiples?
Determining the responsiveness of your flock’s reproduction rate to nutrition can be a useful exercise and gives useful information on the value of feeding extra at joining to lift poor reproduction rates. To do this requires the ewes to be condition scored to tag number at joining (can be when rams come out). At scanning each ewe’s pregnancy status is recorded
against their joining condition/fat score. Those greater than score 3 or more should have a higher reproductive rate than those of <2.5. The difference between the two groups will give an idea of
how nutrition affects the number of dry, single or twin bearing ewes for your flock.
See the conception rate calculator and more details on measuring the reproductive rate of your flock.
See below to download the 'Successful Pregnancy Scanning' factsheet as a print ready pdf.
Acknowledgements
Thankyou to Mark Edwards, Dumbleyung, Aaron Robertson, Darkan and Genstock, Kojonup for sharing information about the needs for accurate scanning results.
Further reading:
CJ Hawkins Homestead, University of New England, Armidale NSW 2351