Vasectomising rams involves removing a piece of tubing that carries sperm from the testes to the penis. Unlike castrated rams, these animals are sexually active but they are infertile.

A group of ewes that are about to start cycling in the autumn can be stimulated to come into oestrus within 24-36hrs after introducing a ram.

This first oestrus is “silent” and infertile. Half the ewes then have a fertile oestrus a week later then again 22 to 24 days after the ram was introduced. The rest return to heat 18 to 20 days after ram introduction. This complicated process leads to the first fertile oestrus of the flock being spread over two weeks.

Vasectomised rams can be used as teasers. They are introduced at the beginning of the season to stimulate ewes to cycle but not get them pregnant. They are then swapped for fertile rams that inseminate the ewes over a 7 day period and so tighten the lambing pattern.

Selecting a Teaser

Choosing the ram to be vasectomised is important. It should be strong and healthy with good teeth, sound feet and no arthritis, brisket or head sores. Young rams are best. They are easier to operate on and have less chance of carrying transmissible diseases. The ram should have some sexual experience and well developed testes and penis. The ram should be permanently identified by tattoo, ear-tag or microchip.

Before the operation, the ram should be bedded on clean straw for at least 24 hours and starved for 12 hours. The operation is done with the ram sedated and local anaesthetic. It is best to leave the ram for at least 3 weeks before releasing with ewes.

Vasectomy is never 100% and if you have any doubts, contact the practice. Regrowth of the tubes that are cut has been known to happen.

The use of Vasectomised Rams

The proper use of vasectomised rams produces a compact lambing period.
They are not useful for breeding out of season.
The ewe flock must be isolated for at least one month from sight, smell and hearing of rams and wethers. The ewes must be on the point of coming into season but not cycling.
The vasectomised rams are put with the flock for 12 days. Ideally, there needs to be 3 teasers per 100 ewes.
The teasers are then removed and replaced by normal rams. The ratio of breeding rams to ewes should be 4 per 100 ewes, because the rams are serving all the ewes in a 7day period.
The ewes come into season in two peaks. 40-60% come into season roughly 3 weeks and the rest at 4 weeks after the teasers were first introduced.
Provided the ewes were on the point of cycling, this results in a close compacted lambing usually in two peak periods six to eight days apart.