Association for the Advancement of Animal Genetics Conference: Adult mature ewe size gets middleweight nod

The Association for the Advancement of Animals Breeding and Genetics Conference involved discussion about a range of livestock topics from sheep to beef and dairy cattle, but the most contentious chat centred on what is the ideal body size of an adult Merino ewe. Agrarian Management consultant Ashley Herbert Ashley, who led this panel discussion on July 27 at the University of WA, said the traits he mostly focused on was the best management of sheep per hectare. “Constitution, thickness, do-ability, whatever you call it — that’s all gold and they make sheep easier to manage to help lift stocking rate — that’s how we make money,” he said. “But do we run a few big sheep or lots of small sheep?” Mr Herbert said buyers usually only bought a certain liveweight, but on the other side of the scale, big sheep were hard to manage. “There is a lower and upper weight limit with a fair gap in the middle,” he said. “Don’t look for a definitive size answer because it doesn’t exist, it’s conditional on a few things. “Sheep are getting bigger on average and there are management implications for different body weights and different types of sheep — we can cap the liveweight of sheep but there are some trade-offs.” Frankland River farmer Alex Coole said her family’s sheep breeding objective focused on dual-purpose, selecting for robust animals that maintain a 19.5 micron wool cut with easy care qualities including worm resistance, polled and no dag. “We focus on performance breeding through Merinoselect using the dual-purpose plus index as a guide,” she said. “During the 1990s with drench resistance issues, our young sheep were more susceptible to worms — it was decided to change the maiden ewe mating from 1.5 to 2.5 years-of-age — this made them bigger animals, about 70kg. “After 10 years and with better worm resistance, we went back to mating the maidens at 1.5 years-of-age with an average weight of 65kg.” Ms Coole said she didn’t think gaining wool cut and worm resistance and increasing weaning weight was made possible through a large framed ewe size alone. “A large framed ewe is not efficient or realistic to genetic gain,” she said. “We want ewes big enough to bear twins but not too big to handle.” She said from conversations she had with WA farmers, there has been an increased body weight in ewes during the last 10 to 20 years. “For reason of breeding a robust and plainer bodied animal, this may have resulted in heavier adult ewes,” Ms Coole said. “My ideal mature ewe weight is 65kg with a condition score three — they are easier to manage from a shearing and husbandry prospective without losing essential wool cut.” Murdoch University adjunct associate professor John Young said liveweight had a lot of effects on lambing production, particularly lamb survival. “The big one in relationship to the implications of liveweight on profitability was feed requirements — the bigger the sheep the more energy they require,” he said. “Metabolic liveweight is a reasonable prediction of energy requirements, but it is not the whole story — weight is not weight.” Mr Young said the animal that was genetically fatter was capable to draw on its reserves during a feed shortage and this allowed the producer to run higher stocking rates for higher efficiency and profitability. “It’s not just about liveweight, there are components to that liveweight including muscle and fat that are important parts of ongoing research,” he said. “The short answer is it’s important to match your production system to your flock’s genotype or vice versa.” University of New England Animal Genetics and Breeding Unit geneticist Daniel Brown said Sheep Genetics was encouraging breeders to think about adult mature ewe size. “The focus on early age growth has created a more rapid increase in mature age size, but the introduction of Merinoselect indexes has seen this plateau,” he said. “As an industry, especially Merinos, we need to manage better and look to bend the growth curve and select for animals with good early growth that can then plateau. “As we push early growth we are also increasing birthweight — Merino producers aren’t recording this trait enough, so there are concerns in this area.” Prof. Brown said it was only a matter of time when Merino breeders would have do more with birthweight recordings. “It’s not just about weight . . . it’s about frame size and composition, there’re separate things,” he said. “The value of these traits are different in varied production systems. “We need to optimise how we select sheep for the type of environment that they need to express.” Prof. Brown said there were variations in muscle, composition and the size of animals. “Bigger sheep eat more and produce more methane which puts more focus on mature size and this barks on a range of new Sheep Genetic’s projects that can analyse the requirements on feed intake and methane so we can actively select for methane and feed efficiencies,” he said. “Average adult ewe size in the maternal data base is 75kg, I’ve heard of producers not being able to get shearers without having to sedate them to get them shorn.” Prof. Brown said seedstock producers were getting price signals to breed rams with early high growth that pushes heavier mature size. “The challenge is for breeders to make other trait selections like eating quality that will do some goodwill and breed rams that will be right for the future,” he said. Mr Herbert said there was an upper limit to bodyweight with real resistance on a 75kg mature bodyweight ewe. “It’s a contentious topic and in terms of liveweight, it is important producers understand their production system — their target market and customer and what is the best production system to achieve success,” he said. “That will tell what sort of animal is required. “If producers are looking to cap liveweight, they will need to use very careful measurements to select the right animals with the right traits — if you’re doing it just by visual assessment, you will probably struggle.” Mr Herbert said using a lot of detailed measurements without giving up many other productive traits would assist producers in capping liveweight issues.