SHEEP breeders have tended to make their flock ewe selection decisions earlier and earlier, according to Merino Lifetime Productivity Project (MLP) program manager and Australian Merino Sire Evaluation Association executive officer, Ben Swain, Gunnedah.
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"And that's for good economic reasons," he said.
However, when overviewing the project at the recent Macquarie MLP field day at Trangie Agricultural Research Centre, Mr Swain suggested there may be a trade-off between making a selection decision earlier on limited or less data, or early-stage data.
"We all grow up in life eventually, and sheep do also, and they also change," he said. "So what's the trade-off for selecting at earlier stages as against lifetime production?
"What's the most cost-effective way to identify ewes that are productive later in life?"
Mr Swain said visual selection was a massive part of the MLP project.
"Because one of the real questions to a commercial breeder was what was the best mix of selection techniques available to get the most gain in a flock, and at what age?
"They include measuring the sheep, classing the sheep and maybe doing a genomic test."
Mr Swain said the project would help to answer these questions for commercial growers and to explore the trade-off between breeding a wool sheep with reproduction or visa-versa.
Can we have a sheep that cuts a heap of good quality wool but still produces lots of lambs of good quality?
Classing
Only 30 per cent of woolgrowers use a classer for ewe selection and that's really surprising because classing can have a huge impact on productivity of a flock, Mr Swain said. "If you do nothing else, you should be classing your sheep."
At the Macquarie site the 2017 drop were classed at eight-to-nine months and then at 29 months after their first lamb.
"We looked at the relationship between a top-graded sheep as a lamb, and wondered what the chances were of it remaining a top-grade as an older ewe," he said.
"We classed at this age specifically because a lot of people are classing sheep earlier and earlier to get rid of what they think are the passengers of the system."
However, Mr Swain asked, was classing at post-weaning too early? "Thirty-one per cent of the top-grade classed at post-weaning stay as top-grade at two years," he said.
Of graded "flock" ewes, 56pc stay as flocks while 40pc of the culls stay as culls."
Of the top-grades at post-weaning, 19pc were classed culls as adults, which is the start of their productive life. However, 16pc of the culled ewes at post-weaning were now among the top-grades at two years.
"This is not a reflection of poor classing, but a reflection of sheep changing," he said.
"Then we see reproduction coming into the mix, and this is a big driver of whether a sheep grades well by just rearing a heap of lambs."
Hoggets
Classing as hoggets the grades stay more consistent.
"But more importantly we are getting less gross error," Mr Swain said.
"Now only 9pc of sheep classed as top-grade become culls and only 3pc of culls change to top-grade."
He said the delay in classing drove production.
"You are choosing better sheep."
Breeders should remember the three tools - visual selection, measurement and genomics.
"They all play different roles and we are going to use them all at different times and in different ways," Mr Swain said.
"We have seen from the earlier data that the later you delay classing at the Macquarie site the better your relationship to lifetime production."
He said for those who join at younger ages, they have to select at an earlier age.
"And we know that not only the visual assessment of younger ewes is tougher, but also objective measurement.
"The early stage wool traits are also less accurate than at the later age.
