DNA tests to help eliminate horn gene | My Machinery
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DNA tests to help eliminate horn gene

New modelling by the Sheep CRC shows DNA testing for the horn/poll gene reduces the chances of breeding horned Merino rams by 80 per cent in one year, completely removes the horn gene from flocks in seven years and from poll flocks in about 20 years. That was if only rams were DNA tested. It was faster – but more expensive – if both rams and ewes were tested. The Sheep CRC’s modelling involved assessing the impact of DNA testing a poll flock with 1000 ewes using 25 rams each year. Each year 10 rams were replaced by young rams and 410 new ewe replacements were needed. The CRC found the number of horned rams produced by the flock could be reduced from six each year to one almost immediately by testing rams that were introduced. Sheep CRC chief executive James Rowe said commercial producers had expressed a preference for polled Merinos which meant there was a clear price differential of as much as $200 in favour of polled rams. “At $17 per DNA test, there is a clear return on investment for breeders and ram buyers wanting polled Merinos,” he said. While the new data and test has been recognised as a good step forward, the Australian Association of Stud Merino Breeders wants the modelling to be viewed in context – there still has to be a focus on wool quality. President Phil Toland said commercial producers probably did not mind if their Poll Merinos were homozygous or heterozygous polls, just so long as they did not have horns. “Most good Merino wool men are really wanting to put emphasise on wool, not whether it’s horn or poll,” he said. “There’s no sense in having poll animals with inferior wool, it doesn’t work, it’s not acceptable.” Mr Toland said there had been a bigger swing to polls for stud breeders. Many studs had renewed interest in Poll Merinos and new studs were starting with polled animals. “That’s a reflection of the market, people see polls as easier care and they are for shearers, handlers and with flystrike where Merinos fight or get caught in fences.” He said there had been a gradual improvement in Poll Merino wool in the past 10 years which was evident in show entries. For the past two years, the Australian Sheep and Wool Show medium wool classes had more polled animals than horned. Professor Rowe said the new genomic test for the horn gene meant that breeders with poll flocks could avoid breeding from rams that were carriers. “While testing rams as well as replacement ewes reduces the frequency of the horn gene more quickly than just testing rams, the cost of testing is much higher and this should be carefully factored into breeding budgets,” he said. Hazeldean’s Jim Litchfield said DNA technology was a new and fast-evolving field. “We are currently evaluating just where it will fit in our overall breeding program. But we certainly see advantages and think the work done by the Sheep CRC has been outstanding. “Utilising their findings to get the most cost-effective gain from genomic technologies will be the key question for progressive stud breeders.” Mr Litchfield said he had seen a preference for poll rams in recent sales. Although the Hazeldean flock was historically a horned flock, he thought there were advantages in poll sheep other than popular demand. “We will never compromise actual genetic superiority on the basis of horn presence or absence however if one of our poll sires demonstrates genetic superiority and, through DNA analysis, shows that he is homozygous poll then we would use that ram widely and particularly over ewes by other polled sires to further instil the poll factor in our flock.” Horn v Poll … the background – Horn development in sheep is controlled by a single gene that is recessive. – Based on the Sheep CRC’s observations of 2300 Merino progeny in the Information Nucleus Flock, there are three possible gene combinations that determine whether a sheep is horned (H) or polled (P) – HH, PH or PP (the marker genotype). – Animals that have horns (HH) must carry the trait from both parents. PH rams are rarely horned and PP rams are always polled. – DNA testing identifies the marker so breeders can determine how likely it is that a ram’s progeny will have horns when mated to ewes with different genotypes. In poll flocks, studs can avoid breeding from rams that carry the horn gene. – For producers who occasionally have horned sheep in their polled flock, the flock is carrying the horned gene. The frequency of the horn gene can be quite high even though there are not many animals with horns. – The CRC says if only one per cent of males appear with horns, the horn gene is still present in about 10pc of the flock. This means that in 10pc of matings, a sire or dam could pass on a horn gene to its offspring. About 18pc of polled rams being used will be horn gene carriers.

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