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Another gene discovery means more lambs

October, 2000
Another gene discovery means more lambs

By Claire Grant, AgResearch

New Zealand is becoming unique in the world for studies into fertility, and it’s all thanks to sheep and sheep scientists.

AgResearch has discovered another gene influencing prolificacy – that is a ewe’s ability to produce twins. This follows on from a significant world breakthrough by AgResearch earlier this year when a major gene known as Inverdale was found and mapped to the sheep genome.

This time the gene has been discovered operating in the Coopworth sheep breed. Its effect is less than the Inverdale, producing an extra 25 percent more lambs, which will be ideal for farmers who want to boost lamb numbers with very minimal effort.

Although the gene’s function has been observed, its actual location has yet to be found. The Woodlands gene, as it is known, is unrelated to the Inverdale gene, although both are located on the X-chromosome. This provides another very interesting dimension to overall knowledge on fertility, because understanding and developing how this new gene works in sheep will provide another level of information on exactly what genes are affecting fertility in general.

AgResearch Invermay scientist George Davis, who originally found both the Inverdale and now the Woodlands gene, predicts sheep will become a very important model for fertility studies in the coming years. “New Zealand is a pioneer in this field, with a resource that’s unique. No-where else in the world are there the numbers of sheep with the sophisticated level of recording and the selection lines of sheep that we have here” Mr Davis said.

About the Woodlands gene
The Woodlands gene has a very different pattern of inheritance to the Inverdale gene, yet it is just as complex, and like the Inverdale, it has some totally distinctive characteristics which will make it interesting to human fertility researchers.

The gene is imprinted, which is an unusual form of inheritance documented in very few mammalian gene discoveries world wide.

A gene with a maternal imprint will only work if it is inherited from the father and will be “silenced” if inherited only from the mother. As if that wasn’t unusual enough, Mr Davis believes there is a further imprinting characteristic going on in the line of Coopworth’s he’s studying which has never been documented before. Rams have to inherit the gene from a mother which has the gene switched off or “silenced,” for the effect to show in their daughters.

Basically this means that animals inheriting the gene may either express it or have it silenced, depending on how they inherit it.

Because it can be passed on to offspring in a silenced form, the gene will therefore not be easy to detect. Testing the progeny of each ram is a very slow and cumbersome way of following its inheritance. The development of a test which identifies a genetic marker is therefore vital before it will be widely used in industry.

A marker is a genetic “signpost” which indicates whether or not an animal is carrying a particular gene. Marker test technology has already been perfected by AgResearch, with genetic marker tests developed for Inverdale and the Booroola prolificacy genes.

AgResearch’s molecular biologists are presently working on a marker test for the Woodlands gene, and although the novel way the gene is expressed makes finding one more difficult, it will only be a matter of time before the discovery is made.
In the meantime, Mr Davis and his team are anticipating strong market interest in the gene, and are “packaging” it in a way that will no doubt be very attractive to the sheep industry, by combining the Coopworth’s dual purpose attributes with the Texel’s maternal and carcass attributes.
The Coopworth Texel cross will mean more lambs from a lean and meaty breed of sheep.An interesting twist to this gene discovery story is that Coopworth sheep carrying the gene are more than likely already widespread in New Zealand’s sheep industry.

Mr Davis can trace the pedigree of his line of prolific Coopworths back decades, right back to the original Coopworth flock which was developed at Lincoln University in 1958 by crossing Border Lester and Romney sheep. These original hybrids were the source of many Coopworth flocks now established throughout New Zealand, and Mr Davis believes the gene will be already having an effect.

However, its unusual imprinting form of inheritance will mean the Woodlands gene isn’t being passed on in an obvious way, and it will no doubt be confusing the interpretation of breeding values.

In other words, it’s likely to be out there, but the gene’s potential for improving prolificacy has not been realised or exploited.

This novel inheritance characteristic will present management challenges to stud breeders when its released, but won’t make any difference to commercial farmers as long as they purchase rams known to express the gene.

At the same time the Woodlands gene offers the scientific world some interesting perspectives on how twinning occurs.

The research that started in the 1970’s with a call to New Zealand farmers to provide ewes that had twins or triplets, to start lines of prolific sheep has well and truly paid off. Prolificacy genes have been identified in both the Romney and Coopworth flocks that were established at AgResearch Woodlands near Invercargill, each with different effects on the sheep’s fertility.

The Woodlands gene has the least dramatic effect on prolificacy, but will still make a huge difference to on-farm productivity, and ultimately to the New Zealand economy. “It will be a very attractive option for farmers who want to improve productivity by using ewes that can produce twins rather than singles.”

And the prolificacy gene search hasn’t finished yet. Mr Davis has further prolificacy trials going on, now on commercial farms around New Zealand. But that’s another story….

For further information, please contact: George Davis,
AgResearch Invermay, Phone (03) 489-9188, Fax (03) 489-3739

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