Many of you reading these blogs have Aberdale ewes, and will know a little bit about the Inverdale gene, but probably don't have a clue where it originated from and how it got to where it is now!
This morning I met George Davis, the man responsibe for much of the early work on Inverdale. George discovered that the prolificacy gene is located on the X-chromosome and as a result of this discovery he was able to establish a commercial gene marker test. George is also the man responsible for naming the gene 'Inverdale'.
Having been involved with ewes carrying the Inverdale gene for the past three years, and having met others that were involved in the early discovery of Inverdale, including Peter Fennessy (former MD of AbacusBio) and Arnie Gray I was extremely keen to meet George. I had previously read articles about the discovery of Inverdale, and when I visited Arnie Gray in New Zealand two years ago he filled me in on the early days of Inverdale. But reading things in a book is never the same as hearing it from the person that worked for decades on discovering what was causing a line of ewes back in the 1970s to be so prolific.
George told me that he was not involved with Inverdale right from the start, as a group of geneticist and scientists (including Pete Fennessy) at Invermay near Dunedin set about searching for flocks in New Zealand with exceptionally high prolificacy. In 1979 a farmer from the Banks Peninsula came forward with a 12 year old Romney ewe that he had bought at the sale yards in Christchurch (mixed in with a group of cull ewes), and who had had 33 lambs in 11 lambings. Embryo transfer and mating from A281, as she became known led to the creation of the 'special family' of sheep that would lead to the identification of the Inverdale gene. Embryo transfer and laparoscopy over the next six years lead to only further puzzle the team at Invermay, who were expecting the prolificacy gene in this line of sheep to react in a similar way to the Boorola gene (which was also identified by George Davis).
It was only in 1986 that laparoscopy results from two tooth progeny of 84-81, a grandson of A281, identified that his daughters had ovulation rates even higher than those from a heterozygous Boorola ram, who were known to have high ovulation rates. However, the progeny from another two grandsons of A281 were no higher than the control group of ewes that carried no prolificacy gene. This confirmed thoughts that a major gene was present, however as it acted in a different way to Boorola (as two grandsons didn not appear to carry the gene) it posed the question as to where the gene was located.
After this John McEwan at Invermay suggested to George that the gene may be located on the X chromosone. It was years later in 1990 that this suggestion was confirmed. In 1987 George Davis mentioned to a group of sheep farmers in Gore that he was looking for 1200 ewes to be used in a progeny test with sons and grandsons of 84-81. Arnie Gray, a sheep farmer that George had previously worked with came forward and offered 1200 Romney ewes that he was trying to improve fertility in. Arnie was disappointed with the progeny test lambing, with a high death rate amongst his ewes and too many were barren. In 1990 the female progeny of the 84-81 descendents were laparoscoped by George and his team as two tooths. At the end of the day George set to work with his calculator and soon had his evidence to show that in fact they did have a major gene for prolificacy on the X chromosome! Three of the lines were Inverdale carriers, and they averaged 72% with three or more ovualtions, with a mean ovulation rate 1.1 higher than the non-carriers.
Despite the success in identifying the X chromosome gene, there was still a need to measure ovulation rates in ewes with two copies of the gene. Female progeny from when 84-81 was mated with his daughters were laparoscoped, and for the first time ever George found small, pink, undeveloped ovaries, known later as "streak" ovaries. George was unsure whether this was due to close relatedness, or the effect of having two copes of the gene. In 1991 25 two tooth ewes that were not closely related were laparoscoped, to find that 12 ewes had these "streak" ovaries. Another 31 double copy ewes were later laparoscoped to once again find that close to 50% had streak ovaries. This left George with no doubt that this condition was associated with two copies of the Inverdale gene. As we now know, if you cross an Inverdale carrying ram with an Inverdale carrying ewe, half of the female progeny will be unfertile due to these streak ovaries.
It was fascinating talking to George, learning about the early days of Inverdale and telling George all about how Inverdale is being used in the UK. It's hard to believe that George and his team were working hard on discovering the Inverdale gene even before I was born! George has now officially retired, but he is the man responsible for the discovery and gene tests for many prolificacy genes including Boorola, Wishart and the Woodland gene, and of course Inverdale! A true gent, and an absolute pleasure to meet him.
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