Friday, March 29, 2024

Puberty under the microscope

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The effect of puberty on reproductive performance and improving embryo survival are just two of the sheep-related projects being undertaken by the AgResearch Animal Reproduction team at Invermay. Animal Production scientists Sara Edwards and Jenny Juengel have been looking at the timing of the onset of puberty and how that relates to reproductive performance. Another project the team is working on is embryo survival and having the ability to increase the number of twins born without increasing the number of triplets.
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Thousands of ewe lambs have been monitored to see when they actually went through puberty. It was found that a percentage, irrespective of liveweight, failed to go through puberty in their first year.

Not only do these late developers miss out on the opportunity to produce a lamb within their first year, they produced fewer lambs over their lifetime.

For those animals not lambed as hoggets, the failure to attain puberty before one-year reduces their lambing rate as a two-tooth.

This difference, Edwards said, is significant, amounting to 20 lambs produced per 100 ewes.

This means that for farmers not mating their hoggets, it could be worthwhile running a teaser ram with a ram harness with the ewe lambs.

This would help determine which ones had gone through puberty in their first year and might also stimulate puberty onset in others. The ones
that have gone through puberty are likely to make the best replacements in terms of reproductive performance.

This also has implications for ewe lamb
management during feed pinches as failure to go through puberty could affect their two-tooth reproductive performance. This means that irrespective of whether they are mated, replacement ewe lambs should be fed as well as possible within their first year.

In a linked study, the team noted that late puberty was a family trait in their research flock and went hunting for the genetic cause of delayed puberty. They found a strong association between the age of puberty and a naturally occurring gene variant.

“Those ewes that were the oldest when they reached puberty had inherited two copies of the leptin receptor gene variant.

“This was a new finding,” Juengel said.

Leptin is a hormone responsible for controlling fat deposition and regulating appetite, and the hormone receptor is known to be associated with the onset of puberty in mice, humans, and cattle.

While the link between appetite, fat deposition, and puberty reflects what is seen in the paddock in terms of heavier ewe lambs conceiving and carrying a lamb, Edwards pointed out that there will also be some big animals that don’t go through puberty and lighter ones that do.

They are continuing their work trying to get a handle on hogget fertility. This includes early scanning at just 30 days after mating to see what is happening with the hogget’s ability to conceive and remain pregnant.

Sara Edwards, left, and Jenny Juengel: Continuing their work to get a handle on hogget fertility.

They will also be using biological modelling to help make predictions about hogget fertility and are looking at ways to improve fertility in years when hoggets may be placed under feed pressure.

The scientists will be working also with the animal genomics team to find out how common the leptin receptor variant is in the national flock. If the genetic variation proves to be the cause of the late puberty, breeding the trait out of the flock could significantly increase lifetime reproductive rates and therefore farm profitability.

Another project the team is working on is embryo survival and having the ability to increase the number of twins born without increasing the number of triplets.

This work was initiated by retired scientist George Davis and has involved multiple scientists and technical staff over many years. Working with farmers such as Peter Wishart and Arnie Gray, they observed patterns that suggested a single gene affected ovulation rate, and genetics that also affected embryo survival.

Juengel said that while ewes may conceive twins there will be a percentage of ewes that absorb one of the embryos before day 35. The ewes will carry on to bear a single lamb and the farmer will never know that eggs were lost.

Increasing embryo survival provides the opportunity to maximise the number of twins produced.

Scientists have been doing some intensive searching for single gene variations to improve embryo survival but have yet to identify these genes.

While Juengel acknowledges they have hit something of a road-block with this work, she hopes that is temporary and new technologies will allow them to continue the search.

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