Wishart gene offers double-barrelled fertility benefits

October 2007
The Wishart gene is the latest in a stable of four sheep prolificacy genes investigated by scientists at AgResearchs Invermay campus, near Dunedin.

Scientist, Dr George Davis, who has headed this programme since its inception is especially excited about the latest find. Not only does the gene seem not to carry any undesirable side-effects but sheep which carry it have a high probability of also having a genetically inherited tendency for superior embryo survival.


The first prolificacy gene investigated at Invermay was the Booroola, which came in with merinos from Australia in the 1970s. One copy of the gene in a ewe produces one extra lamb (ie 100 extra lambs per 100 ewes) and two copies, 1.5 extra lambs (150 per 100 ewes). Colleagues at Invermay discovered the piece of DNA responsible for the trait and a marker test is available.

Few farmers in New Zealand have picked up on this gene because it produces too many lambs to be sustainable for the ewe. It is mostly used overseas, especially in milking flocks in Israel where lambs are removed from their mothers at birth and artificially raised; economic in that country.

Ten years on, the Inverdale gene turned up in Romney sheep in Banks Peninsula. Pluses were that if the ewe had a copy of the gene she would produce an extra 0.6 lambs (60 per 100). Two copies though (one from each parent), and female progeny are infertile.

That could have been the beginning and end of the story, but geneticists at Invermay again came up trumps with a marker test for the Inverdale gene. Now a number of farmers especially in Otago and Southland are mating rams carrying the gene across unrelated ewes. Their daughters which carry one copy of the gene are mated to a meat breed sire.

Move on a decade and the Woodlands gene was discovered in Coopworths and is believed to be quite common in the breed. One copy provides an extra 0.25 lambs (25 per 100).

Again, theres a flaw. The gene is maternally imprinted, meaning if its inherited from the mother its silent (not expressed). A ewe with the gene will never carry a daughter expressing it unless she has been mated with an expresser ram. As yet, a marker test has not being developed so the Woodlands gene is not commercially useful.

The Wishart gene

In the 1990s Southland Romney farmer and ram breeder, Peter Wishart, noticed one of his ewes had bred triplets every year for seven years. AgResearch came on board and after seven years of the flock being closely observed on-farm it was concluded that one copy of the Wishart gene pans out to another 0.5 lambs (50 lambs per 100).

The reason Im enthused is it doesnt carry the over-the top lambing of the Booroola, is not associated with infertility and has no complicated imprinting. On the face of it, the gene should be straightforward to use, says Dr Davis.

Theres not yet a marker test available for the Wishart gene so ewes that carry it cant be identified until they start breeding. However, Davis is confident that Invermay geneticists are likely to identify a marker meaning its presence could be confirmed by a blood test.

However, this wont be straightforward. Unlike some other major genes, the Wishart gene is not on the X chromosome. Identifying on which of the other 26 chromosomes its located, is the major focus of work by the AgResearch team.

Even without a marker test, the Wishart gene may not be too far off commercial release as research has showed up nothing untoward. For now, Peter Wishart has so few progeny-tested rams, that he would want to use them himself. Eventually, he could get to a point of selling rams with the gene although as they carry only a single copy, it would be inherited by only 50% of progeny.

Presuming a marker test for the gene is developed, it will then be possible to identify rams with a double copy and guarantee that prolificacy is passed on.

As yet, no rams carrying a double copy of the gene have been conclusively identified although Dr Davis anticipates that one in four of rams in the current round of progeny testing may have carried a double copy. The remainder are likely to be carrying a single copy or to be non-carriers.

In the meantime, selective breeding is doing the job for Wishart, giving him a lambing rate 40% higher than the average.

"Lamb is the key driver of our incomes in sheep farms so the more we produce, the better profits we have," he says.

Embryo survival

One influence on lambing percentage is increased ovulation rates. Another is embryo survival. Serendipitously, the Wishart flock seems to offer both, with embryo loss about a third of what would be expected.

This double genetic whammy was discovered when Invermay scientists measuring the ovulation rates in the Wishart sheep to see which were carrying the prolificacy gene found that some were going on to scan a consistently higher number of embryos than would have been expected on the basis of ovulation.

We would laporoscope the ewes and say they would scan about X, but lines were consistently scanning a lot more. This went on for two or three years of us saying this was Murphys Law, but then it became obvious that it was an ongoing feature of the flock.

Last year Invermay borrowed 10 rams from Peter Wishart. These were mated with 60 unrelated Romney ewes, with 30 of their daughters retained. Now ewe hoggets, they will be laparoscoped next autumn to measure any differences in ovulation rate then a few months later will be pregnancy scanned and embryo survival compared.

Well be looking for those that shed two (or three) eggs then went on to have less singles (more twins) than expected, says Dr Davis.

The exercise will be repeated for several years, to develop a flock profile.


The heroes in the quest for useful genes are farmers, says Dr Davis. The discovery of the Wishart gene in the flock of one of Southlands most prominent ram breeders, was especially fortuitous.

Working with pedigree records which go back almost to Noahs Ark has been very helpful.

The long-term nature of genetic research means it can be difficult getting reliable funding, says Dr Davis. This has become even more challenging in recent years, with the meat and wool industries strapped for cash, but farmers have been consistently generous with their time and effort.

Ideally, this farmer input would be recognised as in-kind support and matched with dollars, he suggests.

The Invermay teams always on the lookout for something new and Dr Davis urges that if farmers notice any unusual traits in a ewe that they check with him before putting her on the truck for the works.

As the Sheep Improvement Limited (SIL) database grows, it could become a wonderful source of information for researchers looking for traits of possible commercial interest. However, this data is farmers property and could not be used without permission.