What is the optimum culling strategy for increasing lamb weaning percentages?

It is a question which has challenged sheep breeders from time immemorial, as lambs on the ground and marked is the basis for profitability in any sheep breeding operation.

And Mr Swain said knowing when is the best time to cull a ewe for lack of reproductive effort has been the focus of his current research.

"When do we cull dry ewes, dry maidens, lambed and lost, double dries?" he pondered.

"Using data from the AWI funded Merino Lifetime Productivity project, we have calculated the average number of lambs weaned from ewes joined."

Mr Swain then went onto explain the results to the audience, based upon the joining of 308 ewes three times at the MerinoLink trial site at Temora.

"The average number of lambs weaned to ewes joined was 106pc," he said.

"What happens if we cull the dry maidens, remember none of these ewes has been culled for not having a lamb."

In response to that result, Mr Swain then posed the next question - what would be the result if the dry maidens had been culled?

"By taking out 53, we would have actually increased the rate of lambs weaned to 118pc," he said.

"If we took out the lambed and lost, we go to 108pc and if we took out the double dry ewes we would be at 113pc and we took out the double lambed and lost it would be 106pc.

"And if we took those that failed rear a lamb during their first and second lambing out, we would have 116pc."

After analysing that date, Mr Swain said culling dry maidens gave the best result.

"But we need a lot of ewes to replace them if we are to maintain flock numbers," he said.

"So, we need to think about the optimum culling strategy."

And, according to Mr Swain there isn't any clear answer to that question.

"I would say culling those ewes who failed to rear at their first and second lambing, we get a good return in our lambs weaned and we don't have to replace a lot of ewes," he said.

"That might possibly be my preference."

But Mr Swain added, the results do depend upon different environments and different seasons.

While the above data was ascertained at Temora in southern NSW, different results came from the trial at Balmoral, in the western districts of Victoria, and also at Pingelly, in Western Australia.

Mr Swain said three sites, three same flock profiles and three different outcomes suggests there isn't one clear answer, and there are many factors which can have an effect of the ultimate weaning percentage.

"We learnt that it is all about the genetic differences between the ewe bases," he said.

"It is all about the seasons - what impact did it have when two of the sites were in drought for two years?

"It is all about the time of year you lamb.

"Using all the data from the Merino Lifetime Productivity project, which is still being collected, will help us to answer these questions."

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