Chasing Mr Goldenballs’ mutations

In pursuit of Wiltshire lambs who might have inherited the Myomax lean muscle mass gene, farmer and geneticist Nicola Dennis tells how the family went about the testing process.

I wrote about our plans to do DNA testing in our sheep a little while back and I’m sure you have been on the edge of your seats wondering how it went. If you are not a regular reader, I will bring you up to speed.

We have Wiltshire sheep (one of the woolless breeds), they run wild and free on our steep, coastal hills. Last mating, one of us got trigger happy on BidR and bought a fancy-pants ram.

In her defence, this ram was a bargain compared to the other much more fancy-pants rams that she was outbid on. The new ram, Mr GoldenBalls, has the Myomax or GDF8 mutation which increases lean muscle mass in sheep.

We want to introduce this mutation into our flock because we think it might give our completely hands-off sheep a bit of a market edge if/when we want to start selling lambs for breeding. So we decided to DNA test Mr GoldenBalls’ lambs to find out who inherited the Myomax mutation.

The equipment

We ordered the tissue sampling equipment from Allflex via Farmlands. There was a bit of toing and froing on the phone as all parties tried to interpret my order.

To be fair, I did disturb the balance a bit by including custom-printed calf ear tags in the same breath. The equipment costs were more expensive than the estimates in my previous article. Inflation is it’s own pandemic. The sampling gun cost $170, the tissue sampling units were $5.49 each and the calf tags were $4.48/pair.

We use those tags on all our ewes because they are easy to read from afar (which is the closest you will get to our sheep) and we hardly ever lose any. That’s impressive since our sheep view our fences as mere guidelines. But looking at that tag cost in black and white, it was a bit extravagant for this use.

The tissue sampling equipment is a kind of ear tag gun and some boxes of liquid-filled vials (tissue sampling units). The vial goes into the gun, the trigger is depressed and released to reveal a needle. This punches a small hole out of the sheep’s ear which lands in the vial. Under each vial in the box there is a place to write the animal’s tag number which makes matching the sheep to the vial fairly straightforward.

We were a little perplexed about how to get the vial back into the box after sampling because the plastic vial holder comes off when the needle is exposed (our pockets were bursting with these little plastic things by the end) and we ended up awkwardly shoving the vials through holes in the box.

Later we were told vials don’t go back in the box, it is fine to mix them all together in a postage bag. A handy tip that evaded us and all the people who read our “please help” post on Twitter.

Taking the samples

Tailing would probably be a good time to sample lambs, but we don’t dock our sheep. So we rounded ours up in early November. Being pretty close to weaning weight, they were old enough to have an opinion about this intrusion. But they were also a good size to just cram up in the chute and take it like grown ups.

One family member felt his pet sheep “Zippy Zappy” should be put in the priority queue for testing.

Zippy Zappy’s punch site bled a lot more than anticipated. In the following sheep, it didn’t seem to matter where we took the sample, blood was on the cards making our yards look a touch suspicious. But, Zippy Zappy forgave us very quickly and happily spent the afternoon tricking other lambs into coming up the chute for their turn.

As Zippy Zappy betrayed her bio-family, we tried to guess which lambs had the Myomax mutation. Our clipboard contains comments like “chubby wee bum” and “very niiice”. Zippy Zappy was, of course, the best sheep in the whole wide world. We did not sample all our ram lambs. This might have been a mistake. A handful of our ram lambs had tiny scurs on their heads and one had full-blown weapons-grade horns. It might have been useful to have the genotypes of our horny regrets to help get to the bottom of the issue.

The lab stuff

Sending the samples was simple. There was a submission form to download from the AgResearch GenomNZ website which needed to be ticked, signed and posted with the samples.

What was my name and contact details? Which tests did I require? I ticked them all and then wrote “Horns” and “shedding” in too. Just in case they were hidden options. Did I want a 60k SNP chip or an HD chip? On the form I said I wanted a 60k SNP chip because 600k HD chips are for the Harry Hardouts with extra special sires.

I also wrote a short note on the form asking for them to send the raw SNP information, if possible. And, yes of course, I hereby allow GenomNZ to access data from my flock on SIL (Sheep improvement Limited), even though we are not SIL registered.

I went down to the local dairy and forced all the boxes into a postage bag and sent them away.

When they received our care package, GenomNZ sent us a “sample receipt” showing all our scrawls neatly typed out into a table.

The genetic results came via email just before Christmas, after the usual set of Covid delays. A four-week turnaround is usually the norm. Once we had the results AgResearch sent us a three page “Customer Account Application Form” which asked us to list our average monthly trade purchases at three businesses with whom we operate a major trading account. It seemed overboard for genetic testing, and I told them so. In the end, we agreed to abandon the credit application and went with a bog-standard invoice. The bill was $26 per lamb, in case you were too polite to ask.

The results

Results for the gene tests came in a spreadsheet. This housed Myomax (called GDF8 by AgResearch for trademark reasons), GDF9, Inverdale and Booroola (which are three different types of fertility mutations), BCO2 (causes yellow fat) and Micropthalmia (an inherited eye disease).

Half of our lambs had a single copy of Myomax, sorry I mean GDF8 (wink wink), which was to be expected, but exciting nonetheless. None of the lambs spiced it up with any of the other tested mutations which was probably for the best.

GenomNZ apologised that they were not accredited to test for “Horns” or “Shedding” but gave me the raw SNP data to play with to see what I could find. A few SNPS were omitted for commercial reasons and samples don’t tend to yield every single one of the 60 thousand SNP results.

For the “OAR10_29546872.1” SNP that the internet told me was a possible marker for the polled gene in sheep, I could only find results for 19 of our lambs. And since I had neglected to test any rams that actually had horns it wasn’t that easy to tell if I was on the right track.

Science has yet to offer up many clues on the location of the shedding genes in sheep so there wasn’t much to look at there. But again every single lamb was 100% shedding so what, pray tell, would I do with that information anyway. The time will come when I think of something to do with all these sheep genotypes, but today is not that day.

The verdict

We had a lot of fun genotyping our sheep. Was it over $2000 worth of fun? Possibly not. We have a handful of Mr Goldenballs jnrs that look good enough to save from the works. Maybe we can recoup our costs by selling them. We have one spectacular ram lamb (looking at you, number 212) that was a real stand out. Good on paper, even better in the yards. Having that not-so-woolly Adonis probably makes it worthwhile on it’s own.

We also know which of our replacement ewes are carrying the mutation and their DNA results are stored with AgResearch if we want to get into parentage/pedigree analysis further down the track.

We can also be reassured that there is a decent correlation between lambs with “chubby wee bums” and the Myomax mutation. Although it has to be said that with excellent growing conditions in Otago this season, all bums ended up suitably chubby. But some of those bums were better off on the boat to China.

Will we do the testing again next season? Yeah, I think so. If I can find something to do with my growing collection of Myomax Wiltshires, then the rest of my family will probably think so too. Oh and in case you were wondering, Zippy Zappy is now a bonafide member of the Myomax family. She, however, doesn’t identify as a sheep so her contributing to the breeding programme is not a given.