Oestrus Behaviour - Anatomy & Physiology

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Oestrus is the period of sexual receptivity in a female, commonly referred to as 'heat'. For further infomation on oestrous cyclicity, follow this link.

Species Mare Cow Ewe Sow Bitch
Duration of Oestrus 7 days (2-12 days) 15 hours (6-24 hours) 30 hours (18-48 hours) 50 hours (12-96 hours) 9 days (4-21 days)


Expression of Oestrus Behaviour in Relation to Ovulation

Courtesy of In Practice,November 2005.

Oestrus Detection

  • Oestrus detection is critical, as the absence of detection is the most important reason for delayed breeding.
  • A common problem is lack of return to oestrus at a reliable time after parturition.
  • Cows are not often run with the bull, and so detection is the job of the herdsperson.
  • 70% of oestrus activity occurs at night.
  • Groups of cows need to be examined at least 4 times a day at equally spread intervals.
  • Average oestrus detection rates are ~ 60%, the target is >70%!

Standing to be Mounted

Although pedometers are increasingly being used and in-line milk progesterone tests are being developed, the most reliable method for determining the optimum timing of artificial insemination (AI) is the observation of cows standing to be mounted (STBM).

  • Ovulation occurs approximately 30 hours after the first display of STBM, which in turn is 24 hours after the LH surge.
  • The optimum time to inseminate in order to achieve the best conception rates is six to 24 hours after the first observed STBM.

Signs of Oestrus

  • Standing to be mounted is the only truly reliable indication of oestrus.
  • Other signs of oestrus may include:
    • Homosexual mounting
    • Bellowing when isolated
    • Holding milk
    • Brawling
    • Restlessness
    • Chin pressing
    • Swelling of vulva (also when coming into and going out of oestrus).
    • Mucus discharge (also when coming into and going out of oestrus). This is called a bulling string.

Factors Influencing Oestrus Behaviour

Sexual behaviour in cows is itself influenced by numerous factors:

  • Cows tend to be ridden by cows in, coming into or going out of oestrus. The more sexually active females there are, the greater the number of mounts and likelihood of cows being observed standing to be mounted.
  • Lame cows are less likely to show signs of sexual behaviour.
  • Non-slip surfaces encourage sexual activity, while slippery and rough surfaces discourage such behaviour.
  • Lack of space is prohibitive.
  • The presence of a stock bull can be counterproductive.
    • Rarely see a cow actually being served
    • Cow–cow interactions are reduced, thus interfering with oestrus detection.

Aids to Improve Oestrus Detection

For methods of oestrous synchronisation and oestrus induction click here.

Tail Paint

  • Applied to the base of the tail and sacrum.
  • Removed by rubbing when the cow stands to be ridden.
  • Cheap and effective

KaMaR Heat Mount Detectors

  • More expensive
  • Must be identified, as they can become displaced.
  • Pressure sensitive device with a built-in timing mechanism designed to be activated by standing heat behavior.
  • Glued onto the sacrum
  • Pressure from the brisket of a mounting animal requires approximately 3 seconds to turn the detector from white to red.
    • This timing mechanism helps distinguish between true standing heat versus false mounting activity.
  • AM/PM rule still holds: If you see a red detector in the morning, breed her late that afternoon. If you see a red detector in the evening, breed her the next morning.

Closed Circuit Television (CCTV)

  • CCTV with a time-lapsed video
  • Useful during night hours when the cows are not observed.
  • Good cow identification is important.

Teaser Bulls

  • Teaser bulls or androgenised cows will identify cows that are in oestrus provided they have some sort of marker, such as a chin-ball device.
    • The halter has a cone shaped device underneath which contains a freely rotating ball, working on the same principle as a ball-pen.
    • The stainless steel ball container can be filled with ink of the desired colour.
    • Each fill is enough to mark 25-30 cows (approx. 0.5 litre).
    • Marks fade in 4 to 14 days
  • Using bulls risks the spread of venereal disease.
  • Some bulls aquire harems of specific cows.

Clinical Methods and Assessments for Oestrus Detection

Successful oestrus detection is reliant both on observation and the display of oestrous behaviour. If either element is reduced, this has serious effects on detection and thus submission rates.A period of 30 minutes observation at least three times daily is recommended.

Progesterone Levels

  • Low plasma or milk progesterone indicates that the cow is close to, or in oestrus.
  • Milk progesterone assays can be used routinely on alternate days from 25-30 days postpartum.
  • Sampling of milk progesterone to check oestrus identification can be counterproductive: aware that the purpose of this measurement is to ‘investigate’ their accuracy of oestrus detection, farm staff may be tempted only to sample cows that are definitely in oestrus during the period of checks.

Other Methods

  • Detection of a follicle and absence of a corpus luteum by palpation or ultrasound examination of ovaries.
  • Crystallisation patterns in vaginal mucus.
  • Fall in body temperature prior to oestrus.
  • Reduction in vaginal pH.


Oestrus Detection

  • Oestrus detection is only important when Artificial Insemination regimes are practiced and often these are now done following hormonal stimulation rather than waiting for a spontaneous cycle.

Signs of Oestrus

  • Restless
  • Seeks ram
    • Forms a following harem with other ewes
  • Waggles tail
  • Moves tail laterally to allow mating
  • Slightly swollen vulva
  • Slight mucoid vulval discharge

Clinical Methods and Assessments for Oestrus Detection

  • Low plasma progesterone


Oestrus Detection

  • Oestrus detection is a crucial assessment to ensure sows are presented to the boar at the correct time.
  • Good relationship between weaning and return of oestrus, unlike the cow.
  • Observe twice daily remote from feeding time.

Signs of Oestrus

  • Stands for a boar producing lots of pheromones in saliva.
  • Stands very firmly to be mounted, hence the 'back pressure test' is very reliable.
    • But, becomes refractory after 10 minutes standing, then no visible response for 1-2 hours.
  • Vulva swollen and congested 3 days prior to Oestrus.
  • Desire to seek the boar.
  • Other signs include:
    • Restlessness with repetitive grunts
    • Pacing
    • Searching
    • Mounting
    • Being mounted
    • Lowered feed intake
    • Loss of appetite
    • Male-like sexual behaviour:
      • Persuing
      • Nosing
      • Mounting other females
    • Increase in vaginal mucous (requires digital examination)
      • Usually more pronounced in guilts than sows.


  • Oestrous detection is a problem because mares not in oestrus can cause significant damage to a stallion.
  • May be a slight oedema of the vulva and a mucoid discharge.
  • Generally mares return to oestrous about 6-10 days after foaling.
    • Called a 'foal heat' because often the foal develops diarrhoea at this time, which makes the oestrus easy to detect.
      • Fertility may not be high at 'foal heat' oestrus.
  • Mares with an older foal at foot may not show signs of oestrus, as they are protective of the foal ('foal shy').

  • Commonly teasing is performed (usually daily) using a less valuable stallion over a 'teasing board'.
  • Mare will stand as if to urinate, lift her tail and lean her hindquarters toward the stallion.
  • Mare repeatedly exposes her clitoris ('winking')
  • If the mare is in oestrus, the stallion usually demonstrates a Flehmen response.

Clinical Methods and Assessments for Oestrus Detection


  • Detection of a follicle and absence of a corpus luteum by palpation or ultrasound examination of ovaries.
  • Demonstration of follicle size, follicle wall thickening and follicle wall softening on ultrasound.

Vaginal and Cervical Examination

By visual; examination of the vagina and cervix using an illuminated speculum, it is possible to detect the preovulation period.

  • In dioestrus, the cervix is small, constricted and firm.
  • In dioestrus, the cervix and vagina are pale pink and mucus is scanty and sticky.
  • During oestrus, there is a gradual increase in vascularity of the genital tract and relaxation of the cervix with dilation of the cervical os.
  • Approaching ovulation, the cervix becomes very relaxed and its protrusion can be seen on the vaginal floor.
  • Vaginal folds glisten with clear lubricant mucus.


  • Long period of proestrus where the bitch is attractive, but will not allow mating.
    • Characterized by:
      • Vulval swelling
      • Presence of serosanguinous discharge
  • Followed by standing oestrus:
    • Standing to be mated
    • Deviation of the tail
    • Discharge becomes paler in colour
    • Reduction in vulval oedema
  • Poor relationship between time of ovulation and external appearance.

Clinical Methods and Assessments for Oestrus Detection

  • Assessment of vulval softening
  • Assessment of vaginal epithelial cells
  • Examination of the appearance of the vaginal wall.
  • Measurement of plasma progesterone concentration (detecting a rise in progesterone that preceeds ovulation in this species).


  • Oestrus detection is important, for although the queen is an induced ovulator (thus ovulation will not be missed), the LH response to mating decreases with each day of oestrus and follicles ultimately regress.
  • Proestrus is short and often unnoticed.
  • Oestrus is characterized by increased vocalization,rubbing and rolling.
  • Queen is more active and will seek the tom.
  • Stands to be mated by lowering her front quarters and extending her hind legs.
  • Demonstrates lordosis
  • Tail erect and held to one side.
  • Slight mucoid vulval discharge.

Oestrus Behaviour - Anatomy & Physiology Learning Resources
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