AgResearch Invermay farm systems science team leader Peter Smith, of Mosgiel, said teaser rams had been used by AgResearch for "donkey’s years".
A teaser ram has been vasectomised and was sterile and continues to produce testosterone.
A flock of female sheep were given access to a teaser ram to syncronise their estrous cycling, the process of going on heat and ovulating in regular cycles during the breeding season.
"There are a lot of farmers who swear by them," Dr Smith said.
However, the use of a teaser rams on a commercial mature ewe flock did not increase conception or lambing rate, Dr Smith said.
Mature ewes cycle at the right time for an "intact ram" so using a teaser ram was not necessary.
However, a teaser ram could "tighten up" the duration of lambing by having more of mature ewes cycling at the same time.
If a farmer wants his mature ewes to lamb earlier, they could put a teaser ram in a flock of mature ewes for 17 days and then put the intact rams in a month earlier than the usual tupping date.
"With mature ewes there is not a lot of use for teaser rams but hoggets is a different kettle of fish."
Many southern farmers put teaser rams in a flock of hoggets 17 days before they released the breeding rams.
A teaser ram could increase the cycling and conception rate in a hogget flock.
"You’ll get about a 16% in your lambing rate from the hoggets if you use teasers."
"That will do the trick in most cases."
A critical part of a successful hogget lambing was ensuring the flock had an appropriate body condition score.
"If you are not getting the animals up-to-weight, the use of teasers will bring some in that are under weight and that will bring problems."
A skinny hogget was unlikely to hold a pregnancy, Dr Smith said.
He believed if a hogget was up-to-weight and cycling and never mated, she would perform better during mating as a two-tooth, he said.
"With your two-tooths, you will have a higher lambing rate if they have cycled as hoggets."
Reasons farmers did not use teaser rams was the cost of maintaining a teaser ram.
A vasectomy of a ram cost about $200.
Lambs born on the Invermay campus were trucked to the Woodlands Research Station near Invercargill.
As hoggets, their mating process includes teaser and intact rams and they return to Invermay as two-tooth ewes.
The teaser rams at Invermay would be put to use in early April to identify which ewes in a Beef + Lamb New Zealand central progeny test were ovulating before they were artificially inseminated.
"That is the major reason we have them at Invermay," Dr Smith said.
