SELECTION for growth rate increases in Australia’s terminal and maternal sheep flocks has created an industry trend toward bigger heavy ewes, raising efficiency issues for producers and potential health problems for shearers.

New South Wales Department of Primary Industries livestock systems technical specialist Phil Graham said although there had been an industry trend of increasing ewe size, it did not mean it was occurred in every flock.

However, increasing ewe liveweight has become an issue in some flocks recently, prompting resistance to heavy sheep from shearers and flock owner investigation of alternative shearing methods.

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Objective industry-wide data on commercial ewe liveweight and other traits is limited, but Mr Graham said the liveweight of mature first cross ewes used in industry research work in Victoria and New South Wales between 1990 and 2010 increased 15 kilograms, from 60kg to 75kg.

Mr Graham said over that period all sheep sectors – wool, maternal and terminal — had been increasing growth rates. This included breeders of Merinos and Border Leicesters who lifted growth rates in their flocks, fuelling the liveweight gains in Border Leicester-Merino or first cross ewes.

“It is also certainly true in meat sheep breeds,” he said.

Poll Dorset and White Suffolk breeders have told Mr Graham the size of their mature ewes is increasing, with some seeking advice on how they can handle their heavier sheep. A shearing contractor told him his workers were experiencing more hip and knee problems due to increased “wear and tear” on joints because of larger sheep.

“In the last 12 months, the majority of people who have contacted me about handling equipment were breeders of meat sheep.

“In one week I had three Poll Dorset breeders ring me … they said ‘we can’t handle our animals anymore, not like we used to before.’ ”

Mr Graham said rams at 150kg and ewes at 100kg had gone past the point of being able to be physically handled by their owners without assistance, but he did not believe heavy sheep were an industry-wide problem for shearers at the moment.

“But if the rate of increase that we’ve seen in the weight of sheep continues for another 10 years, I think it’s just logical to say that there will be increased problems with the shearing of them.

“Shearers say all you’ve got to be is in the correct position, but the simple fact is we have fewer shearers out there, they can pick and choose where they go and some people are going to find themselves having to look for alternatives,” he said.

“Just don’t blindly think big is better.”

Positive relationship between growth rate and liveweight increase

Mr Graham said there is a strong positive genetic relationship between selection for higher growth rates and increasing liveweight.

“If we increase growth rate, and the same applies to cattle, we’ll increase mature size.

“If you look at sheep industry it has done a fantastic job in improving growth rates, that’s a big plus, he said.

“If we’ve got bigger animals it is giving us a faster growth rate, so the faster growth rate is a plus, but we are losing some of that dollar advantage with the faster growth rate in that we’ve got a bigger animal to feed.

“In the lamb game, if body weight is going up, reproduction has got to go up as well; you just can’t tolerate a bigger animal that is producing no more lambs,” Mr Graham said.

“We’ve just to make sure that if animals are getting bigger, that the positive production traits in growth rate and the number of lambs we’ve got are going up at a greater rate than the negative side of having to feed them.”

Mr Graham said his work in Merinos had shown the rate of increase in ewe size and liveweight could be slowed by selection for early growth rates which plateaued as animals got older, moderating adult body weights.

“We achieved that, we produced a Merino lamb that was maturing quicker with a moderate adult body weight.”

But he said despite putting pressure on early growth, adult liveweights in the flock still increased.

“There will be the odd animal that will be a curve-bender, but a lot of them slow the rate at which adult body weight goes up, I don’t think they stop it.”

Is there a genetic solution?

Mr Graham said Sheep Genetics recently rejigged indexes to put more pressure on slowing the increase in adult ewe liveweights after a survey of SG clients last year showed that mature ewe weight was an issue.

“It’s a start that’s going to have an impact over time, but not straight away.

“As well there will be people who don’t use the indexes and there are people who are attracted to big animals,” he said.

“It’s just something that people need to consider.”

Generating sufficient industry data on liveweight gains and other traits such as reproductive performance was an industry issue, Mr Graham said.

“We would love to have industry data on the differences in reproductive performance between composites and first cross ewes.”

Mr Graham said mature ewe body weights are not routinely measured within stud, commercial or research flocks.

“We measure the growth rates of the rams, growth rates of the young females up until maybe two years of age and after that we stop.

“We don’t measure mature weights, but use correlations to say what is going to happen.”

He said even researchers in the field would like to see mature weights measured to prove correlations were working “and then we know what we’ve got.”