Ram buyers will have a new breeding value to select from in sale catalogues this year to boost the reproductive performance of their flocks.
Sheep Genetics has just replaced its Number of Lambs Weaned (NLW) value with Weaning Rate (WR) which is made up of three components- conception, litter size and ewe rearing ability.
Sheep Genetics manager Peta Bradley- who was one of the guest speakers at the SA Merino Sire Evaluation Day held last week at Malinong- said it would allow Merino and maternal breeders to make more targeted genetic gain.
"NLW has allowed us to make some good progress but the WR is a new and improved analysis as it better accounts for the contribution of the components," she said.
Ms Bradley used an example of two ewes with twins and revealed the data showed that one had given birth to triplets and lost one of the lambs while the other had reared twins.
"I know which ewe I want on my place, I certainly don't want to be feeding triplet bearing ewes or having to manage them if they are going to lose one anyway," she said.
"WR gives better outcomes for lamb survival than NLW."
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The weaning rate breeding value is still expressed in number of lambs weaned per ewe joined but Ms Bradley said the three components were economically weighted for different production systems.
"If you are only scanning 100 per cent (in your flock) the economic value of litter size is quite high, if you increase your litter size you have more lambs to play with," she said.
"But if you are scanning at 170pc you may not want more multiples, it is difficult to keep them alive, so your ewe rearing ability increases in economic importance."
Ms Bradley says the WR breeding value is a "more robust" figure as it using data from updated correlated trait information and more on-farm records.
Genomic testing, which were not part of NLW model, has also been included.
"Reproduction is one of those hard-to-measure, early in life traits but using genomics we can now get a better prediction of a young ram lamb in the marking cradle and how his daughters may perform for weaning rate down the track," she said.
Sheep Genetics has swapped NLW with WR in the FP+, MP+ and DP+ indexes which has led to some re-ranking of animals in the database.
Ms Bradley encouraged breeders to familiarise themselves with the new WR percentile bands which were available on Sheep Genetics website ahead of sales.
"If you were buying rams with NLW above breed average last season we strongly recommend using the percentile bands to re-benchmark what is the new trait average or top 10 per cent etc," she said.
