Vasectomised rams have many different benefits throughout the farming year.


¨    Synchronisation (Concentration) of Lambing

¨    Advancing Lambing Date

¨    Improvement of Lambing Percentage

¨    Ewe Hogget Selection

¨    Identification of Dry Ewes

¨    Timing of Mating

¨    Identification of Ewes in Oestrus for A.I.

¨    Accustomising Non-breeding Hoggets to Ram Behaviour


The synchronisation and advancement of lambing date, plus the improvement of lambing percentage makes use of the “Ram Effect”. The Ram Effect is a powerful natural phenomenon that utilises the effects of male pheromones on non-cycling ewes.

The remaining functions rely on the non-fertile identification of hoggets and ewes that are showing signs of oestrus.


Maximising Lamb Numbers and Early Season Growth.


Most breeds of sheep do not cycle from winter to early autumn. In February when they do start to cycle the first heat is “silent” and the next three cycles result in increasing numbers of eggs being shed.  The Ram Effect can only  be used to manipulate this cycling of ewes at the start of the mating season.


The Ram Effect is a powerful natural phenomenon that utilises the effects of male pheromones on non-cycling ewes.

Pheromones are very potent chemicals secreted in the wool wax of both rams and teasers. The smell of these pheromones produces an immediate and profound hormonal response in the ewe. The ewe’s blood level of the hormones responsible for oestrus (heat)  will increase markedly within half an hour of exposure. The effect is that almost all ewes in the flock will ovulate (produce eggs) within a few days of introducing the males. The exception will be ewes which have already begun to cycle for the year.

The effect only works if ewes are not exposed to the sight, sound and especially the smell of rams (including ram lambs), teasers or bucks for a minimum of 21 days prior to teasers being introduced.


The timing of introduction of the teasers is very important - too early or too late and there will be little effect. 

The beginning of cycling varies between farms and between different years. The main factors are  breed, (with Dorsets and merinos having a longer breeding season than crossbreds), farm altitude, farm latitude, age, ( with hoggets and 2-tooths beginning later and cycling for a shorter period.), and any stress placed on the animals. Two of the main stressors are inappropriate timing of dipping and shearing.

Monitor your own flock to ensure ideal timing.

The Ram Effect and the Use of Teaser Rams

1. Synchronisation (Concentration) of Lambing


By ensuring most of the ewes are cycling  prior to the fertile rams going out you should get a shorter lambing spread with a higher proportion lambing in the first 3 weeks. This is beneficial in all ewes. Often the two-tooths benefit the most from the ram effect. Hogget usually begin to cycle later so the timing is different.


Timing of the introduction of teasers.

The aim is to have the teasers out before the ewes are showing heats, but not too early, as the ewe is not ready to respond. In our region this period of silent heats begins, late February to early March.

This means the date to introduce teasers depends on your tupping date, hence;


 Tupping date prior to the 10th April count back 20 to 23 days.*


 Tupping date after the 10th April count back 37 to 40 days. *


To synchronise ewes, teaser rams should be put into the ewe flock for only 10 days


Teasers can be used at a ratio of between 1:300 and 1:500.

·      This is generally an effective regime, however individual properties vary due to ewe breed, climate, altitude and other factors. There is also slight variation between years. Please feel free to discuss other options with a vet.


Timing of the introduction of teasers in Hogget mating.


As hoggets begin to cycle later  introduce teasers 20 to 23 days prior to the beginning of mating. The exception to this is if hoggets are mated very late, then consider counting back 37 to 40 days.



2.  Advancing Lambing Date


Slightly earlier lambing can be achieved by utilising the ram effect, however to produce truly out of season lambing hormonal treatment is required. The above timing is appropriate.

3.  Improvement of Lambing Percentage


It has been shown that the more cycles a ewe has prior to conception the more chance of having twins.  By using teasers and ensuring all ewes have at least one cycle before mating starts, you may lift your twinning percentage slightly. The program stated in the section on synchronisation at the top of the page is appropriate.


Additional Uses of Teaser Rams


1.  Ewe Hogget Selection


Not all hoggets are equal; - hoggets that cycle in the first winter of life have been found to have a 10% higher performance over the next three years as compared to those that do not.


Hoggets cycle most strongly around the shortest day of the year, therefore, introduce harnessed teasers on the  1st June. The teasers are withdrawn after one month. 

This system can be used in conjunction with other selection criteria - body weight, wool weight, etc.

Teasers should be used at a ratio of 1:100.

2.  Identification of Dry Ewes


Dry ewes usually continue to cycle after the  “real” rams are removed. Identification of non-pregnant ewes is well ahead of pregnancy scanning and can both highlight a problem very early and label ewes for sale.


Introduce  harnessed teaser rams three days after the fertile rams are removed.

A ratio of 1:500  is adequate.

3.  Timing of Mating


By putting out one harnessed teaser ram with 50 ewes you can help determine the optimum time for mating.   When 45 out of 50 have been marked it’s time to put the “real” rams out. 

4.   Identification of Ewes in Oestrus for A.I.


Timing is crucial in an A.I. program,  normally CIDR’s are used and insemination is at a set time, but  identification by a teaser ram of only those ewes in heat can be used. In a naturally cycling flock approximately 6 out of each 100 ewes will be on heat on any given day. It therefore takes 17 days to for all ewes to have at least one heat and be inseminated. Interestingly an estimated 50 million ewes were mated like this annually in the old Soviet Union. 


Details of A.I. programs can be discussed with staff at the clinic.



5.  Accustomising Non-breeding Hoggets to Ram Behaviour


In the presence of rams, in heat mature ewes tend to remain near the ram and will stand for him to mount. Sometimes they will wag their tail stump, nuzzle and even attempt to mount the ram to inform him of their intentions. Young ewes very rarely display these behaviours. This can mean that they when there is competition from older ewes they can have a heat but fail to get served. 

Hoggets can practice these behaviours and be better prepared for mating when mated as 2-tooths.

Teasers can be introduced as part of a hogget selection program at a ratio of 1:100.


Selection & Identification of Teasers


Rams are best vasectomised as 2-tooths so as to have had some sexual experience. Select young sound rams  and clearly, permanently identify them with dual ears tags.

Dorset  breeds appear to make the best teasers. Romney types are satisfactory however.



The Vasectomy Operation


The ram is usually sedated and given local anaesthetic. A length of the tube connecting each testicle to the penis (vas deferens) is removed. The ram will continue to produce the seminal fluid that normally transports and supplies nutrients to semen,  however he has no semen. The testes also continue to secret the male hormone, testosterone.

A recently vasectomised ram should be left six weeks before he is used, this enables any residual semen in  his tubes to become non-functional.