J. D. Bobb, D.V.M.
International SheepLetter
Vol. 19 No. 5, July 1999

Rams secrete pheromones (a hormonal substance that the ewes can smell) from their wool wax which have a dramatic and immediate effect upon ewes which have been kept apart from rams for several weeks.

In a given flock of ewes that are exposed to a teaser ram (vasectomized ram) roughly one-half will exhibit estrus (standing for the ram) at around 18 days after first exposure, and the remainder will exhibit estrus at around 24 days. Therefore, when teaser rams are introduced into a flock of non-cycling ewes, the fertile rams must replace them no later than 14 days after teaser ram introduction. This should result in the majority of the ewes being served over a 10-day period.

The surgical procedure to vasectomizing rams should be completed a month prior to their intended usage. This gives the rams time to heal. Any remaining sperm will be gone from his reproductive tract. You will need to treat the vasectomized ram with antibiotics and fly spray following surgery.

If you plan a September lst breeding date you need to start the process now. Get the ram vasectomized and healed up so that he can be exposed to the ewe flock in mid-August.

The secretion of luteinizing hormone (LH) in the ewe is pulsatile. The main difference between the breeding and the non-breeding season is that the pulses are less frequent during January through June. Within 20 minutes or so of the introduction of a ram to a group of non-cycling ewes, the level and frequency of LH pulses increases dramatically due to the pheromones the rams are carrying.

Ewes within a "teased' group will ovulate within 2-3 days of ram introduction. However, this is referred to as a "silent heat', meaning the ewes are not receptive to the rams. This event, however, starts her natural biological clock and a fertile heat will follow in approximately 17 days in about one half of the ewes. The second half of the flock will short cycle, having another silent heat at 6 or 7 days. These ewes will have a fertile heat at approximately 24 days after the introduction of the teaser rams.

This very useful technique is most successful in the transitional period (July-August) when the majority of ewes in the flock have, not begun to cycle, but are almost ready to.

The use of teaser rams can be used to encourage ewes to breed a few weeks earlier than they would normally. It is used primarily to tighten up the lambing interval and decrease the variation in lambing birth dates. Most producers prefer to lamb as many as possible in the first 17-day cycle to reduce lambing barn hours and to promote a consistent marketing plan.

If you have a large flock, be sure to have adequate ram power to successfully mate the ewes in a short period of time. The success of the synchronized heats depends on the proper ewe-to-ram ratios. This generally means 4 to 5 mature rams per 100 ewes. Ram failure will lead to disappointing results.