WHILE fat has many negative connotations when it comes to consumers and lean meat yield for processors, research has found an extra one millimetre of genetic fat can have a major impact on Merino operations and ease of management.
Murdoch University, Western Australia Sheep Industries Group and Department of Agriculture and Food WA (DAFWA) are researching how increasing genetic fat boosts robustness of Merino ewes.
The focus on storage and mobilisation of fat is because of the role it plays in helping animals cope in fluctuating environments.
At LambEx 2012 in Bendigo, Victoria, in June, DAFWA’s Andrew Thompson said while the research was still a work in progress, early indications were that positive selection for fat in Merino ewes was like a “genetic insurance policy”.
But this is “bred-on” fat, as opposed to intramuscular fat or fat from increased feeding.
In reviewing existing research work and testing some of their hypotheses, the research team found ewes with higher genetic fat were more robust and coped better with fluctuating conditions.
They weaned more lambs and those lambs were more likely to survive.
Dr Thompson said the arguments for fat included improved energy storage, ability to cope with tough seasons, animal welfare, reproduction and taste and flavour.
But the argument against fat included consumer appeal, perceptions around unhealthy fats, wasted energy, costs to processors and lower lean meat yield.
He said Merino sheep had become leaner as a result of selection for higher fleeceweights and the genetic association between higher fleece-weight and reduced fatness.
“Reducing the fatness of lamb to improve its appeal to the consumer has resulted in a general focus on selection for less fat in Australian sheep breeds,” he said.
“Defining the true value of fat requires an understanding of the effect it has on the value of lamb carcases as well as its effects on the productivity of the sheep production system in different environments.”
In trials, his team tested the hypothesis that genetically fatter Merino sheep will have improved performance especially under more restricted nutritional conditions.
Ewes were fed over two months and to a target weight loss of 100 grams a day.
Those that were genetically fatter lost 70g a day, those that were genetically leaner lost 130g/day – an extra 1mm of genetic fat changed liveweight by about 25g/day.
That means over 100 days, the difference in liveweight could be 2.5 kilograms.
Dr Thompson said that small number could translate to quite high differences.
“If I had a group of genetically high fat sheep and they were managed with the low fat sheep and they were at condition score 2.7 at the break to the season, under comparable conditions, below-fat sheep by just 1mm would be condition score 2.4,” he said.
“The significance of that is in the high fat sheep you have about 10 per cent of animals at risk of mortality – those that are under score 2 – whereas about 20pc of the low fat sheep are at risk of mortality.
“The risk of ewe mortality also increases rapidly below condition score 2.”
Dr Thompson said previous research work had indicated the impact of Australian Sheep Breeding Values (ASBVs) for yearling fat (YFAT) on the number of lambs born was not straight-forward.
But his analysis of 44,000 records from ewes in the MerinoSelect database has found an extra 1mm on average of genetic yearling fat is equal to about 18 more lambs born per 100 ewes.
“It is clear that on average there is a positive effect of YFAT on the number of lambs born but the magnitude of the effect varies over a wide range between years and presumably environments,” he said.
Analysis of Sheep CRC Information Nucleus Flock data indicated there was a genetic correlation between fat and lamb survival of 0.34.
The research found that 1mm of genetic fat in tougher conditions translated to 0.4kg in higher birthweight of lambs as well as a 15pc change in survival of twin lambs to 30 lambs per 100 twin-bearing ewes.
“On the ewe side, there’s a number of benefits in terms of genetic fat.
“We can have some confidence that high genetic fat can mean more lambs in utero but a lamb in utero is worth nothing unless you can get it to weaning and beyond.”
Sires with an extra 1mm in YFAT were found to increase lamb survival by 5pc.
Dr Thompson said overall, research had shown selecting to increase fatness in Merinos could improve their robustness to feed deficits by reducing their liveweight loss during summer and autumn, increasing the number of lambs born and improving both lamb and weaner survival.
“Positive selection for fat will make them bullet proof. It’s a work in progress and we still have to nail when fat does deliver the greatest benefits. But when there isn’t time to pile on condition, that’s when genetic fat can come into play,” he said.
“The challenge is that you have no idea of what the genetic fatness of an individual is unless you are able and prepared to use ASBVs.
“In the Merino game, we are talking about yearling fat depth being the indicator of the genetic fatness of that individual.”