Identification of barren ewes by vasectomised rams

The ability of harnessed vasectomised (teaser) rams to identify barren ewes over the 4‐6 weeks after joining with entire rams, has been calculated from 4–6 years' data from 2 flocks. Of the total barren ewes, 29.6% (range 18.2%–46.6%) in one flock and 48.0% (range 31.3%–66.9%) in the other flock were marked in the 4 weeks after joining. The percentage of barren ewes marked by the teasers increased with increasing prejoining live weight of the ewes. There was no effect of breed of ewe on the percentage of barren ewes marked but there were large variations among years. There was only a small increase in the percentage of barren ewes marked when the period of joining with teasers increased from 4 to 6 weeks. The teasers marked 7.1%–8.1% of the total ewes in one flock and 9.5%–10.8% in the other in 4 weeks, but the proportion marked varied among years. In both flocks, pregnant ewes were marked by the teasers, but in all except one year these formed only a small percentage (0.6%–1.2%) of the total pregnant ewes. Culling ewes marked by the teaser rams was more effective in reducing the percentage of barren ewes present at lambing than culling a similar proportion of ewes based on low prejoining live weight or culling ewes with no recorded mating by entire rams.