Pregnancy scanning is a useful tool to help better manage ewe flocks. The two main reasons to scan are to identify twin-bearing and barren (dry) ewes. The costs and benefits of pregnancy scanning depend on the proportions of dry, single and twin ewes. As the reproductive rate increases (total number of foetuses/total number of ewes), the benefit of scanning for multiples increases, compared to the benefit of scanning for just wet/dry. Once above 90% scanning (90 foetuses per 100 ewes joined), the value of scanning for multiples becomes higher than the benefit for scanning on wet/dry alone.
The information can be used to separate mobs into single and twin lambing flocks and better allocate feed according to nutritional requirements. Twin-bearing ewes need to be 0.3 of a condition score better at lambing than single-bearing ewes to maximise lamb birthweight, lamb survival and ewe survival. This means higher feeding rates (unless they are on better pastures than single-bearing ewes). Separating into pregnancy classes allows such preferential feeding to occur. It also allows the number of ewes in twinning mobs to be managed.
Managing the dry ewes can also add value to the ewe flock as they can either be sold, or run as a dry wether flock with maintenance feeding only. This will save substantially on feed as a dry sheep will eat as much as a pregnant ewe for no profitable gain, and will compete for feed when feed is limiting.
Pregnancy scanning is done by ultrasound and needs a skilled operator for accuracy. It should be completed 42–62 days after the rams come out, assuming a five-week mating. The cost of scanning is readily recouped due to the feed saved through better allocation of feed.
Scanning for multiple-bearing ewes
If multiple-bearing ewes are identified the following points should be taken into account:
- Better condition in late pregnancy leads to better survival of lambs.
- Identifying and separating multiple-bearing ewes minimises over-feeding of single-bearing ewes and potential birthing problems with dystocia.
- Multiple-bearing ewes do need more feed but this can potentially come from reducing the feeding rate of single-bearing ewes.
- Consider not scanning for twins if the twinning rate is less than 15%.
- Best results for preferential feeding are seen in a hard year.
- Preferential feeding must be matched with good husbandry — this is especially important if ewes have been managed for high conception rates.
Pre-lambing vaccination and worm control
An annual booster vaccination is recommended for all ewes pre-lambing as there is a level of protection provided to newborn lambs via colostrum of the mother. This will protect the ewe and lamb from clostridial diseases.
Worm control is also important in the lambing ewe, and starts with an effective autumn drench to ewes to reduce the level of pasture contamination with worm eggs during winter. The potential worm problem in the lambs to be born is governed by the level of pasture contamination with worm eggs, and this is largely determined by the effectiveness of the autumn drenching program in the ewes. Thus, it is essential to give an effective (100%) drench at the critical time. For ewes this means drenching in autumn — from mid-March to mid-April.
Additional pre-lambing drenches may be required in some years depending on the season. This is especially likely in ewes lambing later than mid-June.
Monitor faecal worm egg counts and if results are greater than 200 eggs per gram then a drench may be required.