Synchronising oestrous and advanced breeding can yield significant economic benefits for some sheep producers. Debbie James reports
Breeding ewes to capture the spring lamb market can mean premium prices. Producers this year gained an average of £1.30/kg above the returns on summer-sold lambs.
Only one commercial breed bred in Britain, the Dorset Horn, naturally produces lambs all year round and therefore producers are adopting different techniques to synchronise or advance breeding to produce winter lambs which can be slaughtered and sold for a higher price in spring, when lamb is in short supply.
For pedigree flocks, planned breeding enables breeders to produce lambs for the autumn sales.
One farming partnership who used intravaginal progestogen sponges to synchronise 100 borderline cull ewes to lamb in a short period was father and son, Gerald and Mathew Brown, Carmarthenshire. By doing so they achieved £1.30/kg more by supplying the spring market and they also gained £10 a head on the ewes by selling them early when ewe prices were still good.
“We selected our oldest ewes – ones that we would otherwise have killed off. We decided we would get one more crop of lambs before selling them,” Mathew explains.
The Browns breed Whitefaced mules from Brecknock Cheviot ewes crossed with Texel and Beltex rams. Their lambing shed at Llanpumsaint, Carmarthenshire, is too small to lamb all 340 ewes during the same period so it suited the family to lamb the flock in two batches.
1. Synchronising oestrus
They inserted the sponges in August, a procedure they could do without vet assistance. Careful attention was paid to hygiene, with the Browns disinfecting between each ewe and using an anti bacterial lubrication gel to avoid damaging the ewe’s reproductive tract. They removed the sponges after 12 days.
This triggered a sudden fall in progesterone levels and led to oestrus activity within 36-48 hours.
Crucial to the success of oestrus synchronisation is the timing of when rams are introduced to the ewes and the ratio of rams to ewes.
Rams should be turned in with the ewes between 36 and 40 hours after sponges have been removed and the rams should remain with the ewes for at least 48 hours. There should be more than one ram to 10 ewes.
The danger of introducing rams too soon is that they will repeatedly serve the first ewes that show behavioural oestrus and therefore their semen reserves will be depleted for the later ewes. Rams should be reintroduced 16 days after sponges have been removed.
For the Browns it was the first time they had used sponges but are considering using them again this year after one of the best spring lamb seasons in recent years. Their ewes scanned at 154%. The ewes lambed within three weeks, with a high proportion of ewes lambing in the first seven days.
“We sold some lambs in June and the price difference between those and the lambs we sold at Easter was £1.30/kg more for the spring group. We are averaging 18.5kg lambs so an extra £1.30/kg is worth pursuing,” says Mathew, who sells the lambs to the Dunbia abattoir at Llanybydder. “There were extra costs because we fed the earlier lambs on pellets and grass while the later born lambs only had grass and the sponges cost us £2.25 each. But it definitely paid off.”
2. Accelerating the breeding season
PMSG gonadotropin serum injections can also be used in conjunction with progestogen sponges to both accelerate the breeding season by up to two weeks and to synchronise mating. In some animals, PMSG will also increase the ovulation rate, resulting in more lambs for every ewe. This was the reason why the Browns didn’t use PMSG.
“We didn’t want too many multiple births because the ewes were older. We were keen to get one lamb out of each ewe so that they had a better chance of rearing them,” says Mathew.
Vet Gwyn Jones, of Wern Vets, Ruthin, says the dose of PMSG must be selected carefully to avoid the risk of excessively large numbers of lambs. But there is also the opportunity to increase the dosage if ewes have under-performed in a previous season.
“If a farmer has used the product previously we can look at what results he had and, if he was a bit short of lambs, then the dose can be increased,” Mr Jones explains.
However, he says there are disparities thrown up by the season and the condition of the ewes. “There can be a massive difference from one season to the next, depending on the grass growing season and the flushing effect of moving ewes from sparse pasture to better pasture which has the effect of increasing ovulation.”
However synchronisation does have a negative impact on pregnancy rates, he warns. “If ewes breed naturally you would expect a conception rate of between 85-95% but with synchronisation this falls to between 60-70%,” says Mr Jones.
But what should not be overlooked is the convenience of lambing over seven days instead of three weeks, he adds. “Synchronisation is undertaken for convenience while advanced breeding is done for commercial reasons,” he explains.
Another method for advancing ovulation is to implant an artificial hormone, melatonin, under the skin of the ear of early-lambing ewes in June to improve lambing percentages in January.
Mr Jones says the advantage of these implants is that they advance the breeding season without synchronising the ewes which means fewer rams are needed.
“When you synchronise, all the ewes ovulate within 48 hours so you need a high ram to ewe ratio, ideally one ram to eight ewes. That in itself is an associated cost,” he says. “If you are not synchronising the ewes you only need one ram to 40 ewes.”
Melatonin implants can bring lambing forward by two months and has been shown to increase lambing percentages by 20% if given to coincide with normal lambing times.
Trial work on more than 5,000 ewes and ewe lambs of different breeds has shown increased lambing percentages in treated sheep.
It is possible to use both melatonin and sponges to advance the breeding season and to synchronise the ewes. The cost is similar to using a sponge and PMSG injection combination, says Mr Jones.
With all these procedures ewes should be at a condition score of 2.5-3.5 to maximise efficacy.
3. Artificial insemination
Some farmers use artificial insemination, either cervical or laparoscopic, to maximise production. It means they can improve lamb quality by using semen from rams with high genetic merit. It is also an aid to compact lambing.
Mr Jones says cervical AI is relatively cheap – about £2 a ewe – but it is labour intensive because it requires two people to handle the ewe and a third to carry out the procedure. Cervical AI gives a pregnancy rate of about 70%, he says.
There are welfare issues with laparoscopic AI (which deposits semen directly in to the uterine horn), he suggests, and as such this must be a consideration.
“Laparoscopic AI can only be done by vets and there is a welfare cost to it. This should only really be used on pedigree ewes to justify the welfare and financial costs of doing it. It costs around £10 a ewe for this procedure but it does mean that frozen semen can be used,” he says.
The opportunity to use superior sires was the reason why pedigree breeder, Malcolm Evans, used laparoscopic AI. With a small flock of Suffolks and Hampshire Downs he could not justify investing up to £20,000 in a top quality tup.
The procedure was carried out on his farm and he was pleased with the conception rates – 70% on the first and third years and 60% on the second year.
4. Vasectomised rams
One of the least costly methods of advancing breeding is the use of vasectomised teaser rams. Mr Jones says this will advance the breeding season by between one and two weeks, tightening up the lambing period. A major benefit of the ram effect is the synchronisation of oestrous activity. A high percentage of ewes ovulate, conceive and lamb over a short period of time.
Mr Jones recommends two vasectomised rams for every 100 ewes and only 48 hours exposure is sufficient to achieve results. Vasectomised rams must be removed and replaced with fertile rams no later than 14 days after their introduction.
Fertile rams can also be used as teasers, but a small proportion of ewes may become pregnant earlier than required. Because oestrous activity is synchronised following the use of teaser rams, a ratio of one fertile ram for every 25-30 ewes is needed.
Planned breeding provides a number of marketing opportunities for sheep producers. For example: targeting premium Easter lamb prices; evening up batches of lambs; helping pedigree producers produce lambs at the optimum time for autumn lamb sales – as well as tightening up the lambing season. Planning reproduction also allows for more efficient feed management and vaccine application.
It is worth considering using AI, as it provides the opportunity to use semen from genetically superior sires to improve growth rate, carcass characteristics and wool quality. AI also reduces disease spread and the risk of ram failures, especially outside the breeding season, and significantly reduces the number of rams required for synchronised breeding.
For more details, contact your vet. Chronogest CR and PMSG are POM-V products