Detect Heats


3 min read

Symptoms Observation Preparing your team Pre-mating heats Deciding on submission

Understanding cow behaviour is crucial to identify when cows are on heat. Typically, non-pregnant cows will cycle every 18-24 days and a heat will lasts on average between 14-15 hours but can last from 2 to 30 hours. It's important to watch for signs such as restlessness, changes in grazing habits, and physical symptoms like a moist, red vulva and clear mucus discharge. Observing cows after milking will reveal most heats. Ensure your team understands heat detection and shares information effectively. Pre-mating heat detection can help identify non-cycling cows and improve your mating process.

Being able to interpret cow behaviour is critical when detecting cows on heat.

The time when a cow is on heat is defined as the period during which a cow will stand to be ridden by her herd mates or a bull. It occurs every 18-24 days, averaging 21 days in non-pregnant cows and lasts on average 14-15 hours. This time can vary from 2-30 hours.

Every detected heat and successful insemination will result in an average increase of 25kg milksolids in production (21 days x 1.2kg milksolids = 25kg milksolids), and a longer recovery time between calving and mating, increasing the chances of more cows getting in calf the following season.


Cows coming into heat (duration 6-10 hours)

  • Will not stand to be ridden
  • Smell other cows
  • Attempt to ride other cows
  • Display a moist, red, and slightly swollen vulva
  • Are restless and bellow

Cows in heat (duration 2-30 hours - average 15 hours)

  • Stand to be ridden - hair and skin rubbed of crest of tail
  • Are nervous, excitable, and restless
  • May ride other cows
  • May stand with back arched and tail in air
  • Spend less time than usual grazing
  • Display moist, red vulva
  • Clear mucus discharge from vulva
  • May hold milk
  • Frequently change from their usual order coming into the shed - often lead the herd from the paddock or lag behind

Cows after heat

  • Will not stand to be ridden
  • Smell other cows
  • Clear mucus discharge from vulva

Heat Detection - Signs to look for

Video 2:27 min


Observe cows to detect heats about 2 hours after the milking is over - this is when most heats will be observable. Before and after milkings in the paddock and on the race before milking starts are also good times to observe.

During a paddock check, observe cows quietly, paying particular attention to restless groups of cows.

Record the number of every cow detected on heat at each paddock check. Make note of suspicious cows who may be coming on soon.

If several people are involved in heat detection, implement a system to ensure that all involved share their records. For example, a whiteboard at the dairy, texting, or use of apps.

Preparing your team

As mating approaches, start by reviewing the team's heat detection skills - does everyone know what to look for when detecting cows on heat? Then, decide which combination of heat detection aids the team will use during AB.

Never underestimate the benefit of talking your heat detection plan through with your farm team to ensure everyone understands who does what, when, and what to look for. It helps to agree on a system to record numbers of cows spotted on heat. If several people are involved in heat detection, implement a system to ensure that all involved share their records. For example, a whiteboard at the dairy, texting, or use of apps.

Pre-mating heats

Pre-mating heat detection is an opportunity to practise heat detection skills and gain insight into which cows should be cycling once mating starts. It is also the easiest way to identify non-cycling cows, and gain insight on whether intervention is required. It also gives the team an opportunity to practice their heat detection skills before AB starts.

Use tail paint to identify cycling cows. Use one colour tail paint to start, then a second colour to re-paint as cows cycle and need to be re-painted. Within two weeks about half the cycling cows should have been identified. At three weeks, cows with the original colour are the non-cyclers or cows that have had very weak cycles.

Calculate the herd's pre-mating cycling rate, if cycling is less than 75 percent of the herd by 10 days before the planned start of mating, heat detection has not been fully effective and/or there are too many non-cyclers.

At that stage it is time to consider the options to improve heat detection during AB and whether to treat non-cycling cows.

If you have been recording when cows are detected on heat, use this information to anticipate when they are due to come on again, or to help determine if a questionable cow is definitely on heat or not. Look for patterns in recorded dates.

Deciding whether to submit cows

  • Record a "?" in the AB record whenever you inseminate a cow that is possibly on heat but you are not sure.
  • Look up any previous insemination heat records for the cow that is possibly on heat.

Last updated: Sep 2023
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