BIG is not always beautiful – or most economical – when it comes to ewe size, according to New Zealand researcher Chris Logan.
Much like Australia, NZ flocks have significantly increased their ewe weights in pursuit of higher lambing percentages, but Mr Logan said many producers were reconsidering this.
More than 70 per cent of a ewe’s annual feed intake was used for maintenance.
“The biggest single cost in any production system is not buying rams or replacements or fertiliser – it is feed,” he said.
During the Limestone Coast lamb forum at Naracoorte last week, the Lincoln University animal science lecturer shared the results of an extensive Meat & Wool NZ trial, involving more than 600 Coopworth, Romney and Perendale ewes.
It found flocks with smaller ewes (60 kilograms) should be able to turn off an extra 18pc carcase weight a hectare than those based on larger ewes (70kg) of comparable body condition.
Importantly, even though the lambs from smaller ewes were 2kg lighter at weaning, it took just 10 more days for them to also reach the target weight.
The lamb survival rates of the two groups was about the same.
The trial was conducted nearly a decade ago, but Mr Logan said, based on today’s NZ lamb prices and input costs, those with 60kg ewes could produce $450/ha more in lamb sales.
The university’s research also showed there was a diminishing effect of feeding heavier ewes to stimulate higher ovulation rates at joining.
It was therefore better to preferentially feed the smaller ewes in a mob pre-mating.
“NZ breeders are working out preferential feeding before they get pregnant is just as critical as when they are pregnant with singles and twins,” he said.
Many NZ producers who had “hit a ceiling” in lambing percentages have since been focusing on improved ewe efficiency and running more smaller ewes to increase their returns.
“You can have these big beautiful ewes, but your returns per hectare are not good enough,” Mr Logan said.
Mr Logan said a short-term trial had found smaller ewes consumed considerably less pasture than heavier ewes, but further research was needed.
“Time will tell if the increased output makes up for the added cost of running more ewes, but it is looking good,” he said.
