Synchronising Sheep

Author: Shona Young BVMS MRCVS

There are a number of reasons why people may consider synchronising sheep and before deciding which method to use, you need to know what you are hoping to achieve by the procedure. Is it simply a tighter lambing group to ease management and improve disease control? Is it to advance the season so you have early lambs either to meet the spring market, thereby gaining a better price, or to later sell on as pedigree breeding animals? Or is it because you are looking to use artificial insemination so need the cycle to be synchronised artificially?

For each outcome, there will be a method which best suits you but you need to consider both cost, for drugs and/or more rams, and management at lambing time. If you are looking to shorten your lambing period, do you have the staff and space to cope with the same numbers of ewes in a shorter period of time? There are 3 methods for hormonal control of oestrus in ewes which are melatonin implants, progesterone sponges, with or without pregnant mare serum gonadotrophin (PMSG) and teaser rams.

Melatonin implants can advance the season up to 2 months but will not synchronise the sheep for AI purposes and on its own will not condense the lambing period. However, you can condense the lambing period if used with teasers. The implants work by mimicking the effects of shortened day length, during which ewes naturally produce more melatonin which starts reproductive activity. The implant is placed under the skin, 30 - 40 days before the rams go in. There is a delay before the action starts, with peak mating occurring 25 - 35 days after the rams are introduced. Rams are used at 1:50 and the implants do not require removal. This can only be used in ewes which are shearlings or older.

Progesterone sponges are placed into the vagina and on removal 2 weeks later, the sheep are injected with PMSG which synchronises ovulation. This method can be used to advance the season, synchronise for AI and to condense the lambing period. If performing AI, this should be done 55 hours after sponge removal. You can use the sponges without PMSG but this will only condense the lambing period. For both methods, rams are required at 1:10 and this method can be used in ewe lambs.

Teaser rams or vasectomised rams, can be used to advance the breeding season by 2- 3 weeks and to condense the lambing period. This method is not suitable to synchronise for AI. The procedure requires a vet to carry out surgery on the ram under sedation and remove part of the vas deferens, which is the tube that carries semen from the testicles to the penis. This results in a ram which is sterile but still produces "the ram effect" which naturally synchronises the ewes. Candidates need to be sexually mature rams that are physically fit; lame cull rams aren't suitable. The surgery needs to be carried out 8 weeks prior to use to ensure the ram is no longer fertile before being used. The teasers are put with the ewes in the 2 weeks prior to the rams going in at 1:50, with fertile rams at 1:30 thereafter.

Each of these methods have pros and cons, and it really depends on what you are looking to achieve that will determine which is most suitable for you. To achieve the maximum benefits we also need to make sure there are no other issues affecting fertility such as poor nutrition, subfertile rams or infectious disease.

For more information please contact your vet.