Nutritional management to reduce embryo mortality in short-term flushed ewes

Summary

​High levels of embryo mortality reduce the number of lambs born and therefore returns to sheep producers, and there is concern that lucerne pasture may increase embryo mortality.  

Estimated embryo mortality and/or fetal numbers were compared in two studies in which the timing (in relation to conception) and quantity of lucerne available differed.  Embryo mortality was not increased in artificially inseminated ewes fed in pens at maintenance levels of lucerne compared with ewes fed a low-protein pellet, but the proportion of pregnant ewes bearing multiple fetuses was reduced if ewes were fed lucerne ad libitum compared with at maintenance (0.21 versus 0.33) during early pregnancy.

This contrasts with a grazing study which showed grazing naturally cycling ewes on ample live lucerne (estimated energy intake at least 1.8 times maintenance) for 7 days before and to either day 7 or throughout joining increased fetal numbers compared with ewes only grazing dead pasture (1.6 versus 1.3 fetuses/ewe, respectively; lambs marked/ewe joined 115% versus 96%, respectively), with no increase in non-pregnant ewes or returns to service.  

The implications are that producers may achieve large increases in lambing percentages by grazing naturally cycling ewes on lucerne pasture before and during joining, but until further information is known, artificially inseminated ewes should be fed at maintenance levels.