In October of 2021, we had Graeme Martin on the Head Shepherd podcast to talk about teasing in sheep and the biology behind it. This is the first article from that episode.

Graeme has had a long and distinguished career in sheep reproduction. He worked in France and Scotland before returning to Western Australia in the mid-1980s as Lecturer in Animal Science at The University of Western Australia and Research Scientist at CSIRO's Division of Animal Production. Throughout his career, he has specialised in researching the 'male effect' in sheep and has a wealth of knowledge about the science behind teasing.

Graeme takes us through the science of the sheep's brain when it comes to reproduction.

“The sheep is much cleverer than most people give it credit for. It effectively spends its whole day measuring its environment. It measures the length of the night, it measures the amount of food that's available, it measures its body reserves, but also and, in particular, it measures its social surroundings - basically by using smell. And so the sense of smell in the female sheep responds to an odour from a male sheep and this switches on the reproductive system."

"Now there are limitations to this - it is most effective when the animals are not cycling normally. That means, for example, in the period between September and January for merino sheep in Australia. We are lucky that we have got so many merinos in Australia because they really are the best animals for the ram effect and teasing."

"And so what happens is that the female sheep is just wandering around the place and then suddenly she smells a new male. And this is something we've discovered quite recently that it needs to be a new male - a novel male - something she hasn't smelled before. Or maybe she has, but she's forgotten because it was two or so months ago. And so when she smells the smell, her brain switches on, which is within seconds. Two days later, she will ovulate. She won't come on heat with that first ovulation. So she'll go through a cycle and then on the second ovulation she will show heat and can be mated. And that is roughly 19 days after teaser/novel male introduction."

"There is a little bit of a catch here in that after that first ovulation in the first two days, about half of the animals seem to have a short cycle of only about six or seven days instead of 17 days. And they have the second ovulation, therefore, at around nine days. And there's no oestrogen there, either so it's another silent ovulation. The first two ovulations in those animals are silent and then they have the third ovulation at about day 21, and then they come on heat. That's why the recommendation is a 14-day tease because nothing will be back cycling before that. You should have got rid of both those two silent oestruses after a 14 day teasing and then you should have the entire rams in before that next round of ovulation starts."

“You've got sort of peak of activity of sexual behaviour between days 19 and 25 in that period of time. If you have a good percentage of rams, you'll get 70 or 80% of the animals pregnant, which you can then verify later on an ultrasound. This gives you a nice, concentrated lambing. There's a debate about whether you should have the rams present after the second cycle. That's an individual decision. After the second cycle, we don't get much benefit and so it's probably better to pull them out and just keep it concentrated lambing in a nice cohort coming through to the market.”

We all have in our heads this 17 day cycle, and that's obviously an average, not the rule. What is the range and tempo of ovulation?

“15 to 18 days is the range, but you'll get most of the animals on 16 and 17. It is quite reliable compared to other species. So day length decreases, spontaneous ovulation starts kicking in and then teasing is less effective or has zero effect. Once the animals are all cycling, you're wasting your time. There are effects going on in the body in terms of hormones, but you won't have any synchronisation or induction of ovulation."

"So if you were a merino breeder then you might expect the normal seasonal cycles to begin sometime in January, which means that teasing is really only effective up until the middle of January."

You said merinos are the most responsive, but a Romney or a composite, they are later when their spontaneous ovulation starts kicking in - does teasing have an effect on them too, just not as strong?

"Sheep become more resistant to the teasing effect as they become more seasonal. They become less and less resistant as they get closer to the start of the season. So, if you're using a composite with some British genes in there, you can expect the breeding season to be delayed until March. If you go into the end of February, you likely might have a good result with it."

What about mating ewe lambs at 12-13 months. Is it the same sort of process?

"There you've got a sort of strange interaction between the season and the onset of puberty. So teasing can induce an early puberty if the animals are sufficiently mature in terms of the body mass and the body weight and the condition and age. And if you're getting close to puberty, then it's easy to induce early puberty, which is exactly the same experience as you see in the adult ewes. Basically, you can help out the process by using teasing and gain some traction in terms of getting an earlier first pregnancy there."

How long does it take for them to forget a male?

"We don't really know. Basically, we think it's a couple of months. It is an interesting bit of biology because what happens is the female smells a novel male and then in her brain she gets some cell division happening in the memory stems. These new cells make new memories. And then after a while, these cells die. We just don't know how fast they die and therefore how fast the memory disappears. And it's exactly the same process that a female sheep goes through when she smells a newborn lamb. So this process is something that is quite poorly understood. But if you want to be conservative, it would be a few months."

Best practice to keep in mind in this period, is that if you want to use the teasing effect, you want to keep all males in the property well away from where the ewes are. Is one ram providing pheromones enough or is there a percentage that you need?

"The more smell, the better. But generally speaking, you're looking at just a couple of percent, because they wander all over the place. When it comes to putting the entire males in, that’s when you’ve got to be careful. If you're mating during the normal breeding season, then the ram is going to see one ewe in seventeen coming into oestrus every day. That's 6% of the flock coming on heat every day, on average. That's pretty easy for the average ram to keep up with."

"What happens when you’re teasing, is that you’re going to get three, maybe four, times as many per day in that period between the first day 14 and day 26 or 28. So in that period, things are really concentrated and if your ram percentage is too small, they just won't be able to get it all done. You’ll need to bump up your ram power percentage to something like three or four percent. If you're teasing and then single-sire mating, you have to be really careful with your numbers. They're not going to cover the numbers they would in a normal mating."

We have clients putting rams out in November in Australia. Could you just put the rams in two weeks earlier because they shouldn't be spontaneously ovulating?

"The risk is that there's always going to be a few percentage of the flock that are going to be cycling and they'll get pregnant. It's a bit dangerous, which is why teasers have that advantage, being sterile males."

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