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CONTRIBUTOR(S): Vetstream Ltd, Paul Wood,

Detecting estrus

Detecting estrus

Estrus refers to the signs that a cow shows when she is about to ovulate (release an egg from her ovaries). It can last for up to 18 hours.

A heifer displaying the most distinctive sign of estrus as she stands to be mounted ©Mo Kemp

Why do we need to detect estrus?

When a cow shows signs of estrus it indicates that she will be receptive to mating or should be artificially inseminated.

With the increased use of artificial insemination in cattle, the ability of farm staff to accurately identify and detect oestrus in their cattle is crucial to successful reproductive performance.

Estrus detection is often one of the areas that can be most easily improved in terms of herd level reproduction. In herds relying on estrus detection and artificial insemination the economic costs of poor estrus detection can be high – no matter how good other aspects of reproductive performance are, every cow needs an insemination to get in calf.

What are the behavioral signs of estrus?

The primary and most distinctive behavioral sign of estrus is “standing to be mounted” (STBM), as shown by the cow to the far left of the image at the top of this page. When STBM cows will remain immobile whilst being mounted by other cows. STBM is a key behavioural sign of oestrus, however it may only be expressed for short periods of time, with some cows not STBM at all. ​It is important to consider whether the cow being mounted has the ability to move away. For example, the increased use of cubicle systems has led to an increase in misidentification of oestrus in animals stood within cubicles.

Other “secondary” behaviours may also occur including:

  • Restlessness.
  • Vulva sniffing.
  • Chin resting.
  • Mounting and being mounted (without standing).
  • Displaying the flehmen response (curl upper lip back towards the nose)
  • Mutual grooming (such as licking and rubbing).
  • Aggressive behavior.
  • Cows in estrus are often more restless and will tend to take more steps than when not in estrus.

What physiological changes occur during estrus?

Increased levels of circulating oestrogens (hormone) lead to characteristic changes in the genital tract, for example:

  • The genital tract may become swollen.
  • There is increased production of vaginal and cervical mucus, and the mucus becomes less viscous and more transparent. This can give rise to a characteristic “bulling-string”, an outpouring of clear stringy mucus from the vulva upon vaginal examination.
  • Some authors report a reduction in milk yield around the time of estrus.

What methods of estrus detection are there?

Methods of estrus detection include:

  • Direct observation.
  • Heat-mount detectors: these detect mounting behavior.
  • Activity monitors: these detect the increased restlessness of estrus cows.
  • Tests.
  • Bulls/teaser cows.

Direct observation

Observation involves the lowest capital and consumables cost. It can be effective and specific. Best practice recommendations require three, thirty-minute observation periods a day with an observation in the evening.

Observation requires the ability to see the whole herd and as well as clear identification of all cows from a distance. Certain times should be avoided such as feeding, bedding down and when cows are gathered in collecting yards.

Heat mount detectors

Allow the retrospective detection of STBM but need to be checked regularly.

Numerous approaches are available with varying costs:

  • Tail paint or chalk tends to have the lowest cost per application but needs topping up more frequently, chalk is usually applied over the tail-head.
  • Scratchcards are available which can be applied over the sacrum.
  • Kamars are small dye packets which are fixed over the sacrum, they change colour after a period of steady pressure.
  • Heat mount detectors work best when cows have space to express estrus.

False positives are possible, particularly if detectors are placed too far caudally resulting in activation when cows attempt to mount cows not in estrus. False positives are also possible with the use of cow brushes or when cows are bothered by ectoparasites.

Activity monitors

A number of activity monitors are commercially available. Some are leg mounted and measure steps, some are neck mounted and measure activity.

Set up costs can be high but may be offset by labor savings in the longer term. To reduce cost in all year-round calving herds, collars can be “rationed” and only used for non-pregnant cows, this approach is harder in block calving systems where high numbers of activity monitors are needed in the breeding season but can then be redundant the rest of the year.

Activity monitors rely on algorithms to identify cows in oestrus, thresholds may need to be changed to optimise sensitivity and specificity on a given unit. For some systems the activity monitors need time to “learn” a new cows normal activity levels before they can detect the elevated activity associated with oestrus. Activity monitors also rely on cows being able to express estrus and move around.

False positives are possible in times of additional cow activity, for example during handling procedures or at turnout.

Positioning and telemetry systems that work in three dimensions are being explored as a tool for estrus detection.


Progesterone is a reproductive hormone that can be measured in milk via dipstick tests and in-line testing in milking parlors:

  • On-farm progesterone ELISA tests are available but protocols for their use can make them impractical, milk dipsticks are more practical.
  • More regular testing enables more accurate detection of oestrus but is more easily achieved with in-line systems compared to dipsticks.
  • In-line systems are commercially available but currently tend to be high cost and only fitted to new milking machinery.
  • Progesterone dipsticks are perhaps more useful for confirming cows are in estrus if the observer is unsure.

Monitoring of body temperature has been demonstrated to enable oestrus detection, body temperature increases during estrus, vaginal temperature probes have been used experimentally.

Vaginal mucus conductivity changes during in oestrus and probes are available that can detect this.

Using animals to detect estrus

Bulls can be rendered infertile by surgery, such as vasectomy, epididymectomy or via penile translocation procedures. Infertile bulls can then be used to help identify cows in estrus:

  • Worker safety and animal welfare need careful consideration when contemplating using bulls in this way.
  • A chin marker applied to the bull can facilitate identification of estrus cows.

Androgenised cows may be used as an alternative to bulls in some countries where the use of exogenous testosterone is permitted. There are ethical considerations to be contemplated before using cows in this way.

Do I need to keep records?

Good records and communication of identified oestrus events are essential to ensure that inseminations happen consistently and accurately.

Records can also be used to identify cows likely to be in estrus (those identified in estrus or inseminated three weeks previously) for additional attention.

Speak to your veterinarian for further help and advice with optimising your estrus detection.

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