Use in AI
Use in ET

Benefits of Synchronisation Programs

♠ Put simply, to save significant time, especially where larger numbers of animals are concerned. It allows you to concentrate all your heat detection over 1-4 days and hence your AI over this same period. If you want to AI the ones you miss, then you will only have to watch them over a 5-7 day period 3 weeks later. For fixed, timed AI, some do not even use visual heat detection, they simply rely on heat detector patches.
♠ The synchronisation protocols utilising a progesterone implant (CIDR®) can actually bring a cow on (make them cycle) if she was not already doing so – even from 40-50 days post calving.
♠ Also, if you do not do the AI yourself, you can advise your AI tech or vet well in advance about the 2-4 day period that they will be needed. Some of the synchronisation programs even utilise a timed AI, so the AI’s are all done at the same time on the same day.
♠ This also means that your calving will be tighter nine months later, rather than spread over a couple of months.


Negatives of Synchronisation Programs

♠ Cost and safety - you need to purchase & handle drugs. These are hormones and essentially safe products, although prostaglandins must not be handled by pregnant ladies as they may cause abortion, and they may also bring on an asthma attack in those that are susceptible to asthma.
♠ If not performed properly (out of date medications, poor injection technique) then you may not get as many to cycle as you were expecting. This is a rare occurrence however.
♠ Where time is not limiting and you can closely observe your females at least twice daily for up to 25 days, you can use spontaneous or natural heats to do your AI. Here each animal only goes through the yards/crush once – to have the AI performed (compared with 3-4 times for most of the synchronisation protocols).


We have mentioned some pros and cons. What doesn’t change is that all the other variables are the same – good nutrition, good visual heat detection, good quality semen and an experienced AI tech or vet. Generally you get very similar pregnancy rates and you use the same AM/PM rule whether you use a synchronisation program or natural heats. There is no right or wrong method, you simply use the method that suits you and your circumstances the most.

Different Protocols for Synchronisation

All these methods should be used on cows that are at least 40-50 days post calving (60-70 days for first time calvers), are in at least condition score 2.5 and on a rising plain of nutrition. There are many more programs that the ones mentioned here with various advantages & disadvantages, but this is a good comparison of the more well known protocols.

 1)     One injection of PG

Cows are monitored for heat for 6 consecutive days & are inseminated according to the Estrumate (prostaglandin injection)AM/PM rule.
On day 6, those that have not cycled/been inseminated are injected with PG and are checked for heat for the following 6 days and inseminated.
Pros    - simple & cheap
Cons   - will not work on those that have not already cycled
- need to set aside 12 consecutive days to check for heat (vs 3-4 days for the next 2 protocols) but still half as long as watching for spontaneous heats

 2)     Two injections of PG

On day 1 a PG injection is given.
On day 11 (or day 14), a second PG injection is given.
The cows are checked for signs of being on heat 2-5 days after the second injection. (Some recent evidence suggests that allowing 14 days between injections will see more females display standing heat).
Pros     - simple & relatively economical to perform
             - only need to heat detect for 4 days
Cons    - will not work on those that have not already cycled

 3)     CIDR® & PG injection

Application of a CIDR®

On day 0 a CIDR® is placed in the vagina with a special applicator.
On day 7 days (or up to 10 days even) an injection of PG is given.
On day 8, the CIDR® is removed.
* Current thoughts are that there is nearly no difference if the implant is removed on the same day as the PG injection is given. There might be a slight loss of synchrony, but no difference in pregnancy rates. So, these two processes can be safely done on day 7-10 unless you are synchronizing recips for an ET program and want a tighter synchrony.
Females are watched for standing heat 36-96 hours after the PG injection (in fact 2/3’s will cycle within 48-72 hours).
Pros    - tighter synchrony of heat (over 2-3 days) compared with above methods
            - can actually induce a heat in those cows that are not already cycling
           - may give improved pregnancy rates because of prior exposure to progesterone in the implant
            - all this means that potentially more cows can get pregnant to AI in this kind of program.
Cons    - a little more expensive and a little skill needed to insert the CIDR

 4)    Ciderol (Oestradiol Benzoate) EB injections, CIDR® & PG injection

On day 0, a CIDR® is placed in the vagina and 2ml (2mg) of EB is given.
On day 7, the CIDR® is removed and an injection of PG is given.
On  day 8, 1ml (1mg) of EB is given.
Can then start heat detection on the evening of day 8, and most will have cycled by the evening of day 9 (over 24-36 hours).
* Heifers are given half the mentioned amount of EB on days 0 & 8.
* Some also use a 50-100mg injection of Progesterone on day 0 as well – said to help get a couple of percent more females cycling.
Pros     - gives tightest synchrony of heats (most over a 24 hour period), and very strong heats
            - likely to induce more animals to cycle than any of the other methods
            - appears to offer the highest pregnancy rates as well
            - can be used with a 'timed AI' 30 hours after the final EB injection (24 hours for heifers)
Cons    - a little more expensive and a little more complicated but still only 4 trips through the yards.

'Timed AI' is when no heat detection is used and animals are AI'ed at a predetermined time - most AI only those where the heat detector patches have gone off.

 5)     GnRH injections, CIDR® & PG injection

On day 0 a CIDR® is placed in the vagina & a GnRH injection is given.
On day 7 the implant is removed and an injection of PG is given.
On day 9 another injection of GnRH is given.
Most animals will cycle 36-60 hours post PG injection.
Pros     - can be used for timed AI (cows 54-66 hours and heifers 52-56 hours) post PG injection.
Cons    - more variable conception rate (50-70%), because of numerous known & unknown factors.
             - a little more handling and regime a little complicated.

Synchronisation Program

Average number
of females that
actually cycle


Days spent
heat detecting

1) Single PG injection

80% 60%* 12

2) Two PG injections

80% 60%* 4

3) CIDR & PG

90% 65%* 3

4) EB, CIDR & PG Ω

95+% 70%* 1-2

5) GnRH, CIDR & PG  Ω

80-90% 50-70%* 1-2

6) None (spontaneous heats)

90% 60%* 25

* All of these figures can be improved upon by 10-20% in the right hands.
Ω Can used with timed AI (but lower pregnancy rate by 10-15%).

PG         = prostaglandin (Estrumate®, Lutalyse®)
CIDR®  = intravaginal progesterone implant
GnRH   = gonadotrophin-releasing hormone (Fertagyl®)
EB         = oestradiol benzoate (Ciderol®)


Some Points of Note

Re-using CIDR’s - these are the most expensive, single part of any of these protocols, but many believe they can be reused, after cleaning with a soft brush, disinfecting, drying and placing them in a sealed bag again. The Australian version theoretically can be used for a second period of 7 days (& it is even a third) before the progesterone in them runs out. The US version doesn’t have as much progesterone in it & can really only be used a second time. This is off label use - Pfizer, the manufacturer, certainly doe not recommend this.

Estrumate (2ml) or Lutalyse (5ml) – these are considered to give the same results in nearly every trial used. Some vets have a personal  preference for one or the other. The only scientific difference we can fathom is that Estrumate may be more useful in very hot times of year or hot climates.

Reducing wastage of Estrumate – because of the smaller volume of this form of PG, a smaller needle (20G) will see less leakage out the injection hole, and a smaller syringe (2-3ml) will see less error and wastage as well.

Fat animals and injections – use of a 1 ½ inch needle will see the injection fluid deposited within muscle where absorption is much better (compared with injecting into subcutaneous fat itself).

► All treatments are done at the same time each day, and generally in the morning.

► Calf removal at the time of the PG injection in protocols 3), 4) & 5) will increase conception rates by 5% in lactating cows.



1)     Discussion of the CIDR synchronisation programs -

2) Research paper discussing EB, CIDR, PG and GnRH, CIDR, PG protocols -

3) Discussion board for AI technicians with some interesting variations of these protocols & their own experiences & preferences -

4) Research paper discussing use of GnRH in these protocols -

5) Lecture notes on close comparison of various synchronisation programs -

6) In depth discussion of affects of various hormones & protocols on ovulation -