Surrogate sires which essentially act as mobile artificial insemination (AI) units, disseminating high value genetics by natural mating, could become reality in the coming years, Emily Clark, research group leader at the Roslin Institute, University of Edinburgh, told delegates.
While the work is only at the ‘proof of concept' stage and would require further regulation before it became a commercial option, Dr Clark said the technology could significantly enhance the efficiency and sustainability of sheep production in the UK.
The surrogate sires are rams which cannot produce their own semen as a result of editing the gene NAN0S2, but are otherwise physiologically normal and should have all the characteristics of a good ram, e.g. good libido and mobility. They can be of different types, for example, hill or lowland depending on the environment they will be used in.
Donor rams would be those with desirable genetics, for example, higher feed efficiency rates or be lower methane emitting animals. They would donate testicular tissue and then, using spermatogonial stem cell (SSC) transfer, the genetics of the donor would be transplanted into the surrogate rams.
This process will enable the surrogate rams to propagate semen with the genetics of the donor ram by the natural mating process rather than by the use of AI.
The offspring of surrogate sires are not genetically edited or modified in any way, which should eliminate concerns about genome edited products in the food chain.
Dr Clark said: "We would initially create a nucleus flock to produce a small number surrogate sires for proof of concept which could take 3-4 years, but would then be more quickly able to develop multiplier units to supply larger quantities of surrogate rams, which would then able to carry the genetics from a donor ram of choice.
"This means that instead of having one ram disseminating high value genetics we could have thousands which would greatly accelerate the speed at which we can achieve breeding goals offering an alternative to AI for genetic improvement."
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What next for embryo transfer?
The future use of embryo transfer (ET), could be changing according to Ian McDougall of Farmgene. He explained that currently embryo transfer was mainly used for the production of pedigree sheep and was reliant on high prices being paid for some of these animals. There is also the export of embryos to New Zealand, Australia, the EU and central and South America, but again this is dependant on demand from these countries for British sheep genetics.
Mr McDougall said: "The rise in popularity of Texels post foot and mouth in 2001 led to a dramatic increase in the use of ET. The introduction new breeds such as Valais Blacknose, Blue Texels and Dutch Spotted also fuelled an increase in the use of ET which peaked in 2021.
"Not much changed in traditional ET methods from 1994 to 2024 apart from the use of a different superovulation hormone, the use of CIDRS and different anaesthetic protocols.
"However, times are changing. Animal welfare concerns about the invasive nature of ET would lead to a ban on the surgical collection of embryos and regulation of recipient selection.
"There is also potentially a ban on the use of PMSG based on animal welfare issues relating to its production – it is already banned in Switzerland.
"We can work without PMSG, but it will be tricky, and we would need to move ET further into the ewe's natural breeding season and make more use of teaser rams to synchronise ewes.
"There is reduced domestic demand for ET due to less available cash in the sector combined with the rising cost of ET, mainly due to increased vet costs, largely as a result of the cost of superovulation hormones doubling in four years.
"Some breed societies are changing rules to discourage ET and some breeds have completed the ‘ET cycle', that is their numbers are where they need to be."
As to the short term future, Mr McDougall said animal welfare outcomes would need to be considered and an alternative to PMGS found, but ET could be combined with other advanced technologies such as IVF and gene editing and the use of sexed semen.
However, this would be expensive and the structure of the sheep industry would need to change to accommodate this.
On a positive note, future demand for ET could be driven by dam line sires with desirable traits such as high tolerance to round worms or low methane emissions or terminal sire lines with favourable genes for meat eating quality or easy lambing and high lamb survival.
Looking further ahead, Mr McDougall said if the UK sheep industry becomes more like that in New Zealand, pedigree breeding will shrink significantly resulting in very little ET in pedigree sheep. But export may increase if UK sheep have genes desired by other countries. Surgical embryo collection maybe replaced by laproscopic collection, IVF may become more successful and affordable and sexed semen must be available.
ET v IVF
Mr McDougall explained the difference between traditional ET and IVF.
For ET the donor ewe is superovulated to produce multiple ova which are then fertilised, usually by artificial insemination (AI). The fertilised ova (embyros) are collected several days later via laparotomy while the ewe is under general anaesthetic. The embryos are transferred to recipient ewes using a laparoscopic technique or frozen.
Whereas in in-vito fertilisation (IVF) oocyte maturation, fertilisation and embryo development occurs in the laboratory.
Oocytes are collected from un-ovulated follicles using laparoscopy. They are then transferred to the laboratory, matured then fertilised to become embryos.
Embryos are grown to six-day-old blastocysts in specialised media in an incubator.
Success rate is usually about 40% with four to six blastocyst embryos per IVF collection, which are either frozen or transferred to recipient ewes.
This procedure is not widely available commercially in sheep.
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