Sheep farming

Improving ewe fertility – improving profits

With the global demand for lamb increasing by a potential two and a half million tonnes by 20201, UK sheep farmers have to be in a position to take a share of this opportunity. Improved lamb survival and ensuring there is a no stragglers policy will obviously aid with this. There is, however, a large potential improvement by targeting ewe fertility to ensure a consistent lamb crop.

Why improve flock fertility?

As sheep display seasonal oestrus, this means lamb production is in essence seasonal too; this leads to fluctuations in prices due to supply and demand. By using techniques to advance the breeding season, some farms have been able to overcome some of these fluctuations and not only improve cash flow, but also profitability. An earlier lambing time provides an opportunity to utilise spring grass efficiently for lamb production allowing for earlier marketing of the lambs for a faster return on investment. Lambs sold in April and May generate on average a 21% greater return over those sold in the summer months, giving up to an extra £18 per 45kg lamb2.

Synchronisation of a lambing period also has obvious advantages, not only from the perspective of an even batch of lambs for rearing, but from a labour perspective. On-farm labour is one of the biggest fixed costs in a sheep enterprise and the most profitable UK producers have half the labour costs per ewe due, in part, to a condensed lambing period3.Synchronisation also enables the use of advanced breeding techniques such as artificial insemination and embryo transfer. These techniques can lead to fast improvements in the genetic potential of a flock and the lambs. Allowing access to superior rams without the initial purchase costs, a top terminal sire can add £3.50 extra sale value per lamb per year4.

What options are there?

Natural cycling in seasonal breeding sheep commences due to an increase in the hormone melatonin. This is triggered by decreasing day length and then begins a cascade of hormonal interactions which leads to oestrus and ovulation. There are several methods which can be used to alter the breeding season of sheep, which have varying levels of success.

The most commonly used is the “teaser” or “ram effect”; this is where the sheep have not had sight or smell of a male for a period of 4 to 6 weeks. A male is then introduced and the pheromones can bring the sheep into season a few weeks earlier than normal and there will be a small degree of synchronisation depending on where the sheep were in their normal hormonal cycle. The male introduced has to be vasectomised by a veterinary surgeon.

Another method is the use of melatonin implants, these simulate the natural decrease in day length and therefore can advance the breeding season. The implants will tend to induce cycling 60 – 70 days after their use and must be given to the males too, in order to increase the quantity and quality of the semen. They will not, however, synchronise oestrus, so the use of advanced breeding techniques and the potential for reduced labour is not possible.

Injections of the hormone prostaglandin have also been used; these act by removing the progesterone influence of the corpus luteum, allowing the levels of oestrogen to build and the sheep to ovulate if they have a follicle ready for ovulation. This method will allow for some degree of synchronisation of oestrus and ovulation, but will not advance the breeding season due to the need for the sheep to be cycling at the time of injection.

The final option is the use of progesterone devices, such as CIDR® OVIS, these mimic the natural progesterone of the sheep and in essence hold the cycle and allow the development of follicles that are ready for ovulation. Meaning that when the device is removed the drop in progesterone allows for oestrus behaviour and the timed injection of equine chorionic gonadotrophin (eCG) means the developed follicles will ovulate leading to close synchronisation. The use of these devices in this manner also allows the commencement of cycling out-with the normal breeding season, by triggering natural hormonal events. Hence progesterone devices can both advance and synchronise the breeding season.


In European studies in several different breeds of sheep, CIDR OVIS has been shown to be highly effective at stimulating and synchronising oestrus behaviour in ewes at different stages of seasonal breeding5.

Another European study has shown that all ewes ovulated within 58 hours after removal of CIDR OVIS and administration of eCG6. In instances where oestrus is synchronised, knowledge of the point of ovulation can help determine the most successful time for AI and other advanced breeding methods.

CIDR OVIS had less removal issues (P<0.05) than a flugestone acetate sponge7 and 84.5% of sheep showed no or a clear discharge when using CIDR OVIS5.

For further information on how CIDR OVIS can benefit your flock and improve your productivity speak to your veterinary surgeon.

1.Petersen M, Global Sheep Production 2013
3.AHDB Stocktake report 2016;
4.HCC Ram Buyer’s Guide 2009;
5.Zoetis Study A141C-XC-13-019 and A141C-XC-13-020;
6.Zoetis study A141C-ES-15-055;
7.Swelum, A.A-A et al, 2015, Theriogenology; 84, 498–503.

One device should be inserted into the vagina of each ewe to be treated. The vaginal insert should be left in position for 12 days followed by an injection of eCG administered at device removal. The onset of oestrus occurs within 1-2 days after removal of the insert. CIDR® OVIS is presented as a “T” shaped device consisting of progesterone impregnated silicone rubber elastomer skin moulded over an inert nylon spine. Each device contains 0.35 g progesterone. Indicated for the induction and synchronisation of oestrus and ovulation in non-cycling ewes during seasonal anoestrus. For information about side effects, precautions, warnings and contra-indications for this product, please refer to the product packaging and package leaflet. Do not store above 30°C. Keep out of the sight and reach of children. For animal treatment only. POM-V.

For further information please see the product’s SPC or contact Zoetis UK Limited, Walton Oaks, Dorking Road, Tadworth, Surrey KT20 7NS. Customer Support: 0845 300 8034.

Use medicines responsibly ( Date of preparation: March 2018. AH182/18