How to detect heat in cows?


We have talked about colostrum and how to proceed after childbirth to take advantage of all its properties, but that is the end of a long road before that. For all this to happen, gestation must first occur, either by artificial or natural insemination , and we must be attentive.

As in humans, animals also have periods of increased sexual receptivity. A cow is said to be in heat when her sexual receptivity increases in order to facilitate copulation.

This occurs approximately every 21 days, and can vary from 18 to 24 days between oestrus and oestrus, and lasts between 12 and 18 hours, although it can also vary between 8 and 30 hours.

During estrus, estrogen production increases, so that it becomes the predominant hormone until ovulation, which occurs between 10 and 12 hours after the end of estrus.

Ratio of average times between reproductive events (adapted fromHeat Detection and Timing of Insemination for Cattle)



Mounting tolerance

When a cow is in heat, her behavior is affected and it is essential to differentiate and know the most characteristic signs of this state. The most evident is the tolerance to mating, since, as we have said before, their sexual receptivity increases. Therefore, when being ridden, the cow will remain immobile, with the spine arched with the hindquarters slightly raised and the tail deviated.

Secondary signs

Tolerance to mating is the only sure sign of estrus. Then, there are other signs that vary in duration and intensity and can occur before, during or after estrus.

Although they are not as reliable as mating tolerance, they can be used as clues to keep a closer eye on a particular cow and see if she does, indeed, become immobile in the face of a mating attempt. Some of them are:

  • Riding other cows

When cows are in or approaching estrus, they may mount other mates.

  • Altered behavior

In addition to the above, there are other secondary, but equally important, behavioral changes. They are nervous, they moo continuously, they are much more attentive to their surroundings and their activity increases, remaining standing most of the time, unlike their companions.

  • Increased social interactions

Estrus causes an increase in their sociability, so that they form groups with other cows and become closer and friendlier with them. Physically, we can see that they rest their heads on the rump of other cows and smell them, for example. This behavior is known as “ Flehmen’s reflex “.

  • Decreased appetite

As is the case with many humans, they eat and drink less when they are nervous. Consequently, they also ruminate less and milk production decreases.

But, in addition, these behavioral changes are accompanied by physical changes that we can detect simply by looking around a bit.


  • Mucous vulvar discharge and reddened vulva

Normally, when a cow is in heat, we can see that the vulva is more reddened than normal, or that a clear, transparent mucus hangs from it. In many cases this mucus can also be seen on the tail, thighs or perineal region. On the contrary, there are some occasions when it only appears when palpating the cow during artificial insemination.

  • Tail base hair rubbed or matted and dirty flanks

As mentioned above, cows often mount other cows when they detect that they are in heat and, when this happens, the skin on the tail and rump rubs, scratches or mats.

  • Metrorrhagia

If we find bloody slime on the vulva or tail, we can know that the cow had an estrus that began approximately 48 hours earlier.


In 90% of the cases, the cause of poor heat detection is the technique used, either due to factors that reduce the expression of heat signs or poor observation by the farmer.

RUMI. Innogando. Cattle. How to detect heat in cows? Causes of poor detection of jealousy

In the remaining 10% of cases, the problem is the animal and the causes may be multiple:

  • Functional ovarian or follicular cysts
  • Silent zeal
  • Shortened, nocturnal or evening jealousy
  • Or simply have irregular cycles.


To detect estrus in a cow by observation requires great dedication and a lot of time. At least three daily observations of at least 20 minutes’ duration would be necessary and, even then, we would only be able to detect at most 80% of jealousy, since, as we have seen, there are some that take place during the night and others that may go unnoticed.


RUMI relies on these parameters to detect estrus in time. By monitoring the animal’s condition in real time, it is able to record the animal’s activity at all times (resting, walking, eating, grazing and ruminating).

We know that cows in heat increase their motor activity and decrease intake and rumination. Rumi is able to pick up such changes in behavior and, in addition, takes into account other important events that have taken place previously, such as the date of parturition or last estrus.

Thanks to its own application, the farmer will be able to visualize all this and, with this, what we achieve is to allow him both to anticipate them and to be able to act in time.

Bull riding a cow in heat
Luna, one of our cows, captured this scene while wearing a camera around her neck.

- Last entries -

Share this entry


Leave a Reply

Your email address will not be published. Required fields are marked *