Turretfield researchers aiming to improve artificial insemination success rate

SARDI senior research officer Dr Alice Weaver outlined some of this AWI-funded work led by SARDI affiliates Dr Simon Walker and Dr Dave Kleemann, during a recent SA Drought Resilience and Innovation Hub field trip to the centre.

"AI is a really valuable technology for improving genetic gain, using superior sires and sharing superior genetics across the country and globally," she said.

"However far too many producers experience poor results from AI, as low as 20pc pregnancy rate is not uncommon.

"It takes a lot of money to run an AI program so to get a rate of 20pc is really poor.

"Our research work here at Turretfield aims to improve that to 80-90pc."

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Dr Weaver said synchronising a ewe's oestrous cycle was a focus of the research, as oestrus synchronisation protocols have remained largely unchanged in the past five decades since their initial development.

"In a 17-day oestrus cycle, some ewes can ovulate on day one, others on day three - it can vary and be scattered across the cycle," she said.

"The idea with AI is to synchronise the oestrous cycle so that you can inseminate at the correct stage of the cycle."

Dr Weaver said they were trialing different variations of exogenous hormone delivery (prostaglandin, progesterone and equine chorionic gonadotrophin), plus the influence of teaser wethers and ewe nutrition, in an attempt to more tightly control the ewe's cycle.

"When you pull the progesterone pessary (CIDR) out, it should stimulate ovulation," she said.

"We're aiming to increase the flock's chances of getting pregnant by having them ovulate at the right time.

"However we found a lot of variation within the animals after the CIDR was inserted, depending on where they were at in their oestrous cycle - it had a significant impact on the time of ovulation and the success of the AI.

"So [AI success] can all come down to the timing of the oestrus expression and the timing of ovulation."

Dr Weaver said they were also researching the impact of seasons - spring versus autumn - on AI outcomes.

"We found that there is a really big variation in spring compared with autumn," she said.

"The animals performed differently in spring - they're not all cycling at the same time.

"They also get what appears to be luteinised follicles on their ovaries, which may affect hormone production and impact the quality of the eggs.

"SARDI colleague Dr Alyce Swinbourne is currently in the process of analysing the samples for different hormone concentrations.

"We still have work to do to really understand what's going on to improve the pregnancy rates in spring AI programs."

However they did get really good results with an improved protocol in autumn.

"We increased the pregnancy rate by about 15pc, getting up to 85pc success rate at Turretfield Research Centre," Dr Weaver said.

"We now plan to roll this synchronisation protocol out on-farm to test in this next breeding season and we are looking for producers who are interested in being involved."

THERE is also in-vitro embryo production under way in the Turretfield Reproduction labs.

In juvenile in-vitro fertilisation embryo transfers (JIVET), the researchers, led by Dr Jen Kelly, are collecting eggs from ewes between 4-8 weeks of age.

"From birth, ewes have a pool of oocytes in their ovaries and as the sheep cycles, these oocytes grow, mature and then ovulate," Dr Weaver said.

"We in vitro fertilise (IVF) the eggs to produce embryos, which are then transferred into more mature recipient animals.

"The benefit of this is that you significantly reduce your generation intervals, instead of waiting to mate at 12 months of age, you are harvesting oocytes and genetics from the lambs as early as 4 weeks of age.

"In terms of rebuilding the flock and rebuilding superior genetics, JIVET is a great tool, particularly for seedstock producers."

Dr Weaver said they produced 60 embryos from one six-week-old lamb; however there is still huge variation in the quality of eggs both within and between the donor lambs and research is continuing to improve outcomes.

"We are still trying to work out whether we can identify lambs with oocytes that are more likely to develop, as it is a very expensive process, but if you could select a ewe lamb from a very important sire mating and get 60 embryos you could then freeze, it would be a huge gain in trying to rebuild after something like a drought," she said.

The process can also be undertaken on mature animals (MIVET).

"There's also multiple ovulation embryo transfer (MOET), where you stimulate multiple ovulations, AI and then collect the subsequent embryos and then transfer them to recipient ewes," she said.

Dr Weaver said the benefit of these programs was the ability to freeze and bank embryos for later use.

"It would be good to have an embryo bank in case of disasters, such as fire, floods, drought, even disease," she said.