Making More from Sheep Australian Wool Innovation Limited Meat & Livestock Australia
MODULE 10: Wean More Lambs
Tool 10.7
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Pregnancy Scanning is used to identify multiple pregnancies to better manage twin bearing ewes and to identify and remove barren ewes. Careful consideration needs to be made of the costs and benefits of pregnancy scanning to achieve a management and economic gain in the breeding ewe enterprise. Skilled contractors can also scan ewes to age the foetuses conceived in either in the first or second cycle of joining. This information can be used to separate mobs into early and late lambing flocks and better allocate feed and limit the number of ewes in twinning mobs.

The benefit from determining pregnancy status relies on the proportion of drys, singles and twins in the mob. As the scanning rate (foetuses/100 ewes) increases, the benefit of scanning for multiples increases compared to the benefit of scanning for just wet/dry. Above 90% scanning (90 foetuses/100 ewes joined) the value of scanning for multiples becomes higher than the benefit for scanning on wet/dry alone. Figure 1 shows the benefit when the impact of culling dry ewes on the overall flock structure is accounted for.

Figure 1. Pregnancy scanning value per ewe (accounting for impacts of cullling on flock structure)

Reallocation of feed to twin-bearing ewes:

Scanning for multiples allows the twinning ewes to be managed separately. Twin-bearing ewes need to be 0.3 of a Condition Score better than single-bearing ewes at lambing to ensure good birth weights and survival and optimise the lifetime production of their lambs. In average seasons it is most profitable to reduce feed for the dry ewes and give more to the twin-bearing ewes. In poor seasons it is more profitable to reduce feed for the dry and single- bearing ewes and give more to the twin-bearing ewes.

Dealing with dry ewes:

Identifying the dry ewes can add value to the ewe flock through managing them differently, ie. selling them or giving them less feed and running them as a wool producing flock only. Dry ewes cost less to run as they can be run as a wether flock, producing a good fleece on 7 MJ energy/ day. Leaving the non-pregnant ewes in the lambing flock costs money as they will eat as much as pregnant ewes for little additional benefit and they will compete with pregnant ewes when feed is limiting.