As most livestock farmers will be aware, a healthy cow or a post pubertal heifer will have a heat (oestrus) every 21 days or so. I say “or so” because the actual normal range is 18 to 24 days.

On the laws of probability, if you have 100 females in a group, between four and five will come into heat every day over the 21-day cycle.

The purpose of a synchronisation programme is two-fold. Firstly it condenses the animal’s naturally occurring heats into a shorter period and, secondly, hormone treatment can bring forward a heat and get an animal back cycling sooner.

There should be no need to use blanket synchronisation programmes on healthy milking cows

The majority of synchronisation in the dairy herd is carried out on maiden heifers and the main objective here is to reduce workload and condense the calving pattern so more heifers will calve earlier in the season.

Synchronisation is also used on milking cows, but mostly as an aid to get late-calving cows back in calf sooner, or to treat cows with a problem.

There should be no need to use blanket synchronisation programmes on healthy milking cows.

There are generally three hormones that can be used in a synchronisation programme.

These are prostaglandin (PG), progesterone and gonadotrophin-releasing hormone (GnRH). All of these hormones are prescription-only medicines and can only be used under the supervision and direction of a vet.


The most common approach to synchronising heifers is to mate to natural heats for seven days and then give a shot of PG to the remaining heifers not served.

The majority of these heifers should come bulling over the next five days.

Those that don’t can get a second shot of PG 18 days after the first heifer was served, although many farmers will just let the heifers run with bulls after 14 days of observations as the majority should have been served.

Another option with heifers is to give a double shot of PG. The first shot is given 13 days before mating start date and the second shot is given 11 days later, two days before the planned start of mating.

Prostaglandin can also be used to bring forward a heat on milking cows

Using this method, all of the heifers should be served within a three-day window. The thing to remember when using PG is that the animal must be cycling for it to work.

With heifers, this is best assured by making sure they are at target weight at mating.

Prostaglandin can also be used to bring forward a heat on milking cows. Some use it to synchronise healthy, cycling cows in order to condense and increase submission rates.

However, it is more commonly used to bring forward the heat of late-calving cows or cows whose heats have been missed.

Whether PG on its own will be effective at this will all depend on whether the cow is actually cycling – that is has a corpus luteum on its ovaries. The cow would need to be scanned by a vet/trained technician in order to verify this.


Progesterone-based synchrony programmes are more often used as part of a fixed-time AI (FTAI) programme but not necessarily so. Progesterone is a pregnancy hormone, released in higher doses when females are pregnant. A progesterone device, commonly referred to by the brand names CIDR or PRID is placed into the animal’s vagina and left in place for between six and 10 days.

Prostaglandin is used as part of the progesterone programme and, where fixed-time AI is being practised, GnRH will be used also. There are different protocols for FTAI so the best policy is to discuss the most suitable protocol for your farm with your vet.

At a recent Teagasc webinar on breeding, Stephen Moore from Teagasc outlined the recommended FTAI protocol for late-calving cows and heifers. These are outlined in Table 1 under the FTAI heifers conventional semen and FTAI milking cows column.

There is one less yarding with the Teagasc heifer protocol compared to the cow protocol.

Stephen suggested that synchronisation programmes should be used on problem cows to increase the number of cows bred in the first three weeks of the breeding season.

These problem cows include non-cyclers, those with a calving or health issue and, of course, late-calving cows who are at greater risk of not going back in calf.

However, it is essential that cows being put forward for FTAI need to be calved at least 30 days before going on to the programme.

Sexed semen

The FTAI heifer protocol should differ slightly when sexed semen is being used.

Because sexed semen has a shorter “shelf life” in the uterus it should be used slightly later than conventional semen. Because the shot of GnRH times ovulation, the protocol for sexed semen gives the GnRH between six and 16 hours before the sexed semen is inseminated.

This means there will be an extra yarding required when using sexed semen but it will be worth it if it means a higher conception rate is achieved.

New research conducted at UCD shows that sexed semen has the ability to increase profitability on dairy herds.

Donal Walsh’s research shows that where sexed semen is used on heifers with good fertility, the profitability of the farm increases by €31/cow.

Choosing a protocol

When it comes to heifers, the things to consider are the availability of time, labour and handling facilities.

The increased interest in FTAI stems from the fact that heifers are on out-farms or with contract-rearers who may or may not have the skills or time for heat detection. FTAI does away with the need for heat detection.

No heat detection aids are required, at least not for the first round of AI

However, it is much more costly with all the drugs coming in at around €35 per animal plus the cost of AI and arm service.

No heat detection aids are required, at least not for the first round of AI.

Farmers are encouraged to run bulls with the heifers a few days after service and then remove the bulls and apply heat detection aids for a period of two weeks from the start of the third week after service.

Conception rate

Depending on conception rate, about 30% of the heifers would be expected to repeat.

It is important to stress that FTAI protocols also require labour and extra help will be needed, particularly where there are large numbers of heifers.

Administering all the shots and putting in the progesterone devices is a slow process and needs to be done correctly.

The timing of the AI is also critical and where there are large numbers the heifers should either be split into batches or a few people will be needed to do the AI.

In brief

  • Synchronisation programmes can make breeding and calving more compact.
  • Appropriate protocols should be discussed with your vet.
  • The lowest cost approach for heifers is seven days observation and PG for the remainder.
  • Fixed-time AI is expensive but can be used to minimise the number of observations required.