The impact of maternal sire breed and individual sires on the age at which crossbred ewe lamb offspring reach puberty was investigated as part of the Maternal Central Progeny Test (or MCPT). Ninety-one rams were mated to Merino or Corriedale ewes at three eastern state sites over three years, to produce over 6,000 first-cross progeny. These sires represented 20 different breeds and four hybrids.

Both the breed of maternal sires and individual sire genetics within breeds were found to influence the lambing percentage of their ewe lamb offspring. In general East Friesian, Finnsheep, Booroola Leicester and Border Leicester sired crossbred ewes had the highest lambing and weaning percentage when joined at seven months, while Corriedale sired crossbreds had the lowest percentage (see Table 1). Some individual sires had a much higher performance than others within the same breed, this emphasises the importance of LAMBPLAN ASBVs for producers who wish to successfully join ewe lambs.

Table 1: Indicative lambing percentages from different sires in the MCPT

Are there any negative effects to joining ewe lambs?

No detrimental effects were seen in ewes that lambed at one year of age. In fact, ewes that successfully lambed and weaned at least one lamb as yearlings (12 months) went on to wean 12% more lambs (at two and three years of age) than ewes that were dry or failed to rear a lamb.