17/06/2026
Breeding on a Calendar - Article 7: Lutalyse and Prostaglandins
I've posted a few videos recently talking about this, but I know a lot of you save the articles.
Lutalyse is one of those products people mention quite a bit when talking about breeding protocols.
“Give Lutalyse.”
“Did you lute them?”
“Use prostaglandin.”
“She needs a shot to bring her in.”
But if we're going to understand controlled breeding, we need to be careful with the language.
Lutalyse does not simply “bring females into heat.”
That is the shortcut explanation.
The better explanation is this:
Lutalyse helps remove a natural progesterone source when a responsive corpus luteum is present.
That may sound more complicated, but it is much more accurate, and once you understand progesterone, this will make a lot more sense (hopefully).
- The corpus luteum is the target -
Progesterone is the holding signal.
A CIDR adds a temporary progesterone signal.
But... the female may also have her own natural progesterone source.
That source is the corpus luteum, often referred to as the "CL".
The CL forms on the o***y after ovulation, and its job is to produce progesterone.
- As long as the CL is active, progesterone stays elevated.
- As long as progesterone is elevated, the reproductive system is being told:
"Hold still. Do not start over yet"
That's why the CL matters.
If a female has a functional CL, she has a natural source of progesterone inside her body.
- Prostaglandin removes the hold -
Lutalyse is a prostaglandin product.
More specifically, "it contains dinoprost, which has prostaglandin F2-alpha activity".
Other products (such as estrumate) may use different prostaglandin analogs, but the basic reproductive idea is similar.
Prostaglandins act on a responsive CL and cause it to regress.
That regression is called "luteolysis".
Luteolysis basically means breakdown or regression of the corpus luteum.
- When the CL regresses, progesterone drops.
- When progesterone drops, the hold signal is removed.
- Then the reproductive system can move toward the next heat and ovulation.
So the real sequence is:
Functional CL → prostaglandin → luteolysis → progesterone drops → system can move toward estrus
That is different from saying:
“Lutalyse causes heat.”
It is more accurate to say:
"Lutalyse removes the progesterone brake if the animal has a responsive CL".
- It only works if the target is there -
This is the part people miss.
- Prostaglandin is not working on an empty o***y.
- It is not creating a cycle from nothing.
- It needs a target.
That target is a functional, responsive CL.
- If the female has not ovulated, she may not have a CL.
- If the CL is too young, it may not respond the same way a mature CL would.
- If the female is truly anestrous and not cycling, there may not be a CL to regress.
If she's pregnant, the consequences can be SERIOUS because progesterone may be supporting that pregnancy.
This is why timing matters (a lot).
- Why protocols combine CIDRs and prostaglandins -
This is where synchronization starts to make more sense.
- A CIDR adds a controlled progesterone signal.
- A functional CL produces natural progesterone.
If we remove the CIDR... but the animal still has a CL producing progesterone, the body may still be receiving a hold signal.
So some protocols include prostaglandin to remove that natural progesterone source.
In simple terms:
- CIDR: adds a controlled progesterone signal.
- Lutalyse/prostaglandin: removes a natural progesterone source from the CL.
Those are different jobs, but they're part of the same strategy.
The protocol is trying to control progesterone from two directions:
the artificial source (CIDR) and the natural source (CL).
- Prostaglandin is not PG600 -
This is another source of confusion for some folks.
PG600 and prostaglandin are not the same thing.
They both have “PG” floating around in conversation, but they are doing very different jobs.
PG600 is a gonadotropin product.
It is used for a different purpose, involving ovarian stimulation and follicular/ovulatory signaling.
We'll get into that later (in the next article).
- Why “more” is not automatically better or needed -
Because prostaglandin has a specific target, more product is not automatically better science.
- If the CL is responsive, the goal is luteolysis.
- If there is no responsive CL, increasing the dose does not magically create one.
If the animal is pregnant, the concern is not whether the shot “worked.", the concern is that removing progesterone support may compromise pregnancy.
This is why protocols, labels, veterinary direction, species, timing, pregnancy status, and withdrawal considerations matter. Many veterinarians will have a detailed schedule for you to follow based on your specific animal (especially when you are looking at AI/LAI).
- Why some females show heat after Lutalyse -
When prostaglandin successfully regresses the CL, progesterone drops, and that drop allows the reproductive system to move toward the next follicular phase.
- Follicles can continue developing.
- Estrogen can rise.
- Behavioral heat can become visible.
- Ovulation can follow.
So yes, a female may show heat after Lutalyse, just don't confuse that by assuming it's a "heat hormone". The heat happens because progesterone falls and the system is allowed to move forward.
- The pregnancy warning -
I've already mentioned this multiple times, but this article would be incomplete without saying this one more time directly.
Prostaglandins can be dangerous in pregnant animals!
If a pregnancy is dependent on progesterone support from the CL, causing CL regression can result in pregnancy loss.
The same tool that'll reset a cycle can also remove the hormone support needed to maintain pregnancy.
That is why prostaglandins need to be handled with respect.
- The practical lesson -
- Lutalyse and similar prostaglandins are not fertility shots.
- CIDRs add a controlled progesterone signal.
- Prostaglandins remove a natural progesterone source.
Hopefully, as we are rolling along through this series, the steps you take and drugs you give to control breeding are starting to make more sense.
Next in the series:
Article 8 - PG600 and Gonadotropins
We'll look at why PG600 is very different from Lutalyse, what gonadotropins are trying to stimulate, and why ovarian response depends on more than just giving “the shot.” And of course, my favorite topic when talking about PG600.... more is not better.
