Saturday, March 30, 2024

Double trouble

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Could more twins push deer industry productivity? Can twinning hinds be genetically selected for? How do the survival and growth rates of twins compare with single fawns? These are some of the many unanswered questions on twinning which deer farmers and some scientists would like answered. Over the last eight years hinds from the known twinning families have been retained in a bid to further increase the number of twins – in that time twinning has been more consistent. Last year the fawning rate was 104% with 121 fawns from 116 hinds.
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Carterton deer farmers Gavin and Barbara McManaway are convinced that twinning is the result of genetics.

“It’s definitely genetic and it’s the hind genetics that are the driving force,” Gavin says. 

Since 2004 the McManaway’s hinds have produced 21 sets of twins and one set of triplets. 

“We’ve averaged about three sets of twins each year.” Gavin says.

They have farmed deer since 1987, and since the arrival of the first set of twins in 1988, they’ve kept on coming. They have fully recorded their herd – building up a detailed profile of the twin bearing hinds – most of which can be traced back to the hind that produced the first set. 

Over the last eight years hinds from the known twinning families have been retained in a bid to further increase the number of twins. In that time twinning has been more consistent. Last year the fawning rate was 104% with 121 fawns from 116 hinds.

“We suspect there are not many deer farmers in New Zealand that can say that. From a production point of view they must be a bonus.” 

This season only two sets of twins were born.

“What’s interesting is that the hinds are mother and daughter.”

Quite a few of the twins turn out to be both stags so end up in the velvet herd.

“The weird thing is our twin stags are some the best velveters which is probably at odds with what you’d expect.”

He has used the twin stags as sires but there has been no noticeable influence on the twinning rate.

The McManaways are keen to find out more about the general incidence of twins in farmed deer but say it’s difficult because most farmers don’t record their herds.

They would like to see more research into the potential of twinning in deer.

“It’s frustrating. We’ve implemented our own systems to see what we can do to improve the twinning situation but no one seems to think we’ll make much progress. We think that 104% fawning is a fairly impressive statistic.”

Testing for twins

The McManaways have used twin stags as sires without any noticeable influence on twinning rates.

AgResearch scientist Dr Geoff Asher is keen to pursue the topic of twins and says there are probably options for genetic selection of twinning hinds.

Setting up a national genetic register would be one way of picking up higher fecundity bloodlines but reliable identification of hinds would be difficult.

“There’s the danger of over or under-recording twins. Sometimes hinds will cross suckle and sometimes they’ll have a couple of fawns following them but they may not necessarily both belong to the one hind,” Asher says.

But even if genetic selection was pursued he’s unsure whether it would have an industry-wide influence.

“The nearest corollary is with cattle where a lot of research institutes around the world have actively grouped twinning herds of cattle with the view of increasing the overall incidence of twinning. It worked at a herd level but didn’t translate nationally or internationally.”

‘The nearest corollary is with cattle where a lot of research institutes around the world have actively grouped twinning herds of cattle with the view of increasing the overall incidence of twinning.’

Asher estimated 15 years ago that 1-in-200 scanned pregnancies were twins but says that is probably closer to 1-in-100 because of the combination of more artificial insemination (AI), improved genetics, plus bigger and better fed hinds.

The only research on twinning in deer was carried out by Dr Mark Fisher in the mid-1980s.

A prime objective of his post-doctoral fellowship project was to induce twinning using an immunological technique but it was largely unsuccessful. The most twins resulted from gonadotropin hormone injections. 

“The results weren’t particularly encouraging but a lot has changed in that time,” Asher says.

Hinds are bigger and generally in better condition – and more are conceiving twins – because of the combination of improved genetics and environmental factors.

Also, AI has influenced the overall twinning picture – in the deer progeny test (DPT) 2%-3% of AI hinds produced twins. Asher would like “proof of concept” concerning induced twinning to help quantify the survival and growth of twins and overall productivity of the hind.

“We know from the DPT and research programmes and the survival of twins is 70% and 90% for singles. We know that the twins are smaller, but not a lot – what would be good to know is the growth rates of those twins. There’s a lot that needs to be quantified.”

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