Artificial breeding in sheep can range from using teaser rams right through to embryo transfer. Angela Calvert talks to veterinary surgeon Dan Fawcett about some of the available options.
Artificial sheep breeding strategies may be thought of as only for pedigree breeders, but Dan Fawcett, of D. and C. Fawcett Sheepbreeding Services, Penrith, says they have a role to play in many flocks.
He says: “All sheep producers are looking to improve management, genetic gain and ultimately profitability and there are a number of artificial techniques they can use, many of them without the need for veterinary input.
“It might just be using teaser [vasectomised] rams to ensure ewes are cycling before putting the tups in or semen testing rams.
“Then the options of using melatonin implants to control seasons, sponges to synchronise tupping time, artificial insemination [AI] either cervical – which can be done by the farmer – or laparoscopic which needs to be done by a vet. There is also embryo transfer [ET], which again is a veterinary procedure.
“Whatever method you use, it is important to plan ahead and pay attention to detail to remove as many limiting factors to conception as possible.
“Finding out a ram is infertile only after ewes start returning can waste many weeks, impacting on management and profit.”
He recommends rams are semen tested prior to use and says it is something farmers can be taught to do themselves.
“Once you have done a couple of tests you will know what you are looking for. It does not require expensive equipment, a cheap child’s microscope or even a magnifying glass will do. The biggest expense is the artificial vagina [AV] which will cost £70-£100. It also takes time and skill to train a tup to use the AV, but 90 per cent of rams will do it.”
Mr Fawcett says it is important to get a representative sample of semen and this is best done using a teaser ewe and an AV.
“Do not expect a tup to come to the job cold and if a ram has been running with ewes, rest it before testing otherwise you may not get a true sample.
“The second best option is to have the ram in the presence of a cycling ewe and use an electro ejaculator. I would only use just an electro ejaculator on its own as a last resort.”
For successful AI and ET programmes and natural service where it is desirable for a batch of sheep to lamb at the same time, synchronisation of oestrus is required. This involves a progestogen sponge being inserted into the ewe’s vagina for 12 days. On removal she is injected with the hormone PMSG and will be ready to serve or AI two days later.
Whatever the system, preparation of ewes and rams is very similar to ensure health is at its optimum to maximise fertility. This should include making sure worming and vaccination programmes are implemented well in advance of the tupping season.
It is essential any mineral and trace element deficiencies are addressed before tupping as copper and selenium, in particular, are important for fertility.
Mr Fawcett says: “When checking rams testicles take into account what is normal for the breed. For example, Beltex have smaller testicles held high up, whereas Bluefaced Leicesters tend to have bigger, more descended testicles.”
In terms of body condition scoring, Mr Fawcett says he likes ewes to be about 3.5, but is happy for rams to carry more condition as they will start to lose it when they start working.
Fertilised embryos at the stage of transfer to the recipient
The cost of an extended lambing period has been widely documented in terms of management and cost and most producers are aiming to keep this window as short as possible.
Mr Fawcett says: “To have some control over the start of lambing and to keep it tight you have to intervene, even if using natural service.”
If ewes are required to be served ahead of their normal breeding season melatonin implants can be used. These need to be inserted six weeks before introducing tups, eight weeks before AI.
Mr Fawcett believes using teasers is vital to get a flock cycling, especially when wanting ewes to lamb at the beginning of the period which is appropriate to their breed.
Teasers should be introduced five weeks prior to mating for natural service and three weeks prior to sponging for an AI or ET programme.
The teaser effect works best if ewes have not been near a ram (including strong lambs) for a month before they are introduced.
Embryo transfer involves super-ovulating the ewe, by a series of hormone injections, so she produces a lot of eggs, rather than one or two. She is then AI’d and the fertilised embryos are then flushed out at five or six days old and transferred into recipient ewes which have been programmed to accept the embryo and continue the pregnancy.
Mr Fawcett says: “Teasers can provide a huge amount of information and if using AI, raddle the teasers when they are put back with the ewes after the sponges have been pulled. You will then know if the ewes have come in season.”
Mr Fawcett also adds using AI and ET is the fastest way to make genetic gains within a flock, but this can only be achieved by using very good rams.
“It gives you a huge amount of flexibility. Using frozen semen gives you access to a wider gene pool and means you can use rams you could not afford to buy. You can use semen from deceased rams making use of bloodlines which otherwise would not be available.
“AI also makes sharing tups more practical. The average conception rate for AI using fresh semen is 75 per cent and 65 per cent using frozen semen.
“By using ET you are able to make genetic gains on the female side as well which speeds up genetic progress even more by producing multiple lambs from the same parents in one season. It is the quickest and most cost-effective way of setting up a good pedigree flock. It is not without risk, as it is a surgical procedure involving anaesthetic.”
For ET, Mr Fawcett says ewe, as well as ram, selection is important. Using ET can cost between £100-£200 per lamb on the ground, plus the cost of recipients and donors and rams/semen, so is only worth doing if you would otherwise be prepared to pay £1,000 to £1,500 for gimmers.
He says: “You also need to be aware there can be big variations within flushes, more so in some breeds than others. Where there has been more line breeding, flushes are often more consistent.
“If you are thinking of going into ET you have to be aware you will have good years and bad years, but you have to stick at it. There is an inherent variability in the success of flushes. The average conception rate for ET with frozen embryos is 50 per cent and 80 per cent plus with fresh embryos.
“Ideally, if you can flush four ewes at a time they should average out to give a satisfactory result overall. Personally, if you are thinking of starting an ET programme I would buy an older ewe, one which is proven, perhaps from a top flock dispersal. If you do want to buy gimmers I would wait until they have had one crop of lambs and flush them in the second year when they are likely to be more productive.
“They will also have had time to acclimatise to your farm environment in terms of nutrition, pathogens and parasites.
“It is not always a good idea to flush ewes which have been prepared for a sale as they can be overfat. Trying to get them to lose weight pre-tupping will mean they are in a negative energy balance, whereas they should be in a positive energy balance approaching tupping time.
“The same principles apply when buying-in females to use as recipients. A common mistake is to buy them just before you do the procedure. Again, they may be overfat, plus they will not have had time to adjust to your farming system. I would always advise buying ‘recips’ as ewe lambs, let them grow on and start their preparation early.”