RECENT field observations made by SRS Merino breeders, Mark and Vicki Murphy, of Karbullah Poll Merino Stud, Goondiwindi, Queensland, suggest that lamb survival was increased when rams with high Australian sheep breeding values (ASBV) for eye muscle depth and fat cover were used.
By contrast, lamb survival was about 20 per cent lower when sired by rams with low breeding values for muscle and fat.
During the last decade there has been a significant shift in many Merino flocks to selection for meat production to increase profitability.
But the focus of the meat industry on meeting the wants of the consumer for lean cuts by selecting against fatness has come at a cost of Merino reproductive performance.
Mark Murphy, an early adopter of ASBVs, said that strategic use of breeding values has significantly increased profitability for the Karbullah flock and his commercial clients.
"By using ASBVs in tandem with the SRS Breeding System, we have observed that sheep with the genetic capacity to lay down muscle mass with high fat cover early in life are able to maintain good body condition during drought, pregnancy and lactation, and rear more lambs with fewer lamb losses," Mr Murphy said.
The Karbullah results back up a previous study by CSIRO Livestock Industries, Murdoch University and the Sheep CRC.
It demonstrated that selecting for a combination of higher carcase muscling and higher growth, while not selecting against fat, produced better all-round results than breeding for either higher muscling or higher growth alone.
Lead researcher in the project, Mark Ferguson of Murdoch University and Department of Agriculture and Food WA, assessed the whole-of-farm value of fat and concluded that fatness should be maintained or increased in the Merino.
"We found that the whole of farm benefit of a genetic increase in fat was a direct function of its effects on reproduction," Dr Ferguson said.
"In addition there was a positive YFAT effect on lamb birth weight when ewes were on restricted nutrition during pregnancy."
SRS studbreeders are among the leading users of Australian Sheep Breeding Values (ASBVs) through the national Merinoselect program.
The SRS Group looks set to achieve its goal of having 100 per cent of its 40 registered studs using ASBVs by the end of 2011.
Commercial producers using the SRS breeding system have seen major improvements in survivability and reproductive fitness across a wide range of Australian environments, from the Snowy Mountains of NSW to the hot and vast pastoral country of Longreach, Qld.
Most SRS Merino flocks see lamb marking outcomes of 120pc to 130pc.
This high fertility is associated with the SRS sheep type being plain bodied with a calm temperament, high milk production and instinctive maternal bonding - all of which enhance lamb survival.
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