oestrus

IPA/ˈiːstrəs/
IPA/ˈestrəs/

oestrus — noun

1. the stage in a female animal's reproductive cycle when she can become pregnant a

1.nounC2
Definition

the stage in a female animal's reproductive cycle when she can become pregnant and will mate with a male; the British spelling of estrus, used mostly when talking about cows, horses, dogs, and other non-human mammals.

Example

The dairy farmer watched closely for signs that his cows were coming into oestrus.

collocation: come into oestrus

Female cats in oestrus often cry loudly at night and rub against furniture.

pattern: in oestrus (state description)

Common collocations
  • come into oestrus
  • in oestrus
  • enter oestrus
  • signs of oestrus
  • synchronise oestrus
Synonyms
  • estrus

    the American spelling; same meaning

  • heat

    informal everyday term, especially for dogs and cats ('the dog is in heat')

  • rut

    used of male deer, sheep, and goats during the mating season, not the female cycle

Antonyms
  • anoestrus

    the resting phase between oestrus periods, when the animal is not fertile

Grammar Patterns

in oestrus

come into oestrus

Usage Note

Uncountable; appears mostly in veterinary, zoology, and animal-husbandry contexts. Standard collocations are 'in oestrus' (during the period) and 'come into oestrus' / 'enter oestrus' (begin the period). Rarely used of humans — for the parallel human cycle, writers say 'ovulation' instead.

Common Mistakes

The woman was in oestrus during her ovulation week.
The woman was ovulating during that week of her cycle.
oestrus describes non-human female mammals; for humans use 'ovulation' or 'fertile window'.
She had two oestruses last spring.
She came into oestrus twice last spring.
oestrus is uncountable; describe repetition with verbs or time phrases, not a plural noun.

Word family

  • oestrous
    adjectiveC2
  • oestrogen
    nounC1
  • anoestrus
    nounC2

Synonym discussion

Sense: noun/1

These four terms all touch on mammalian mating cycles but differ in register and reference. 'Oestrus' is the British technical spelling used in veterinary medicine, zoology, and animal science; 'estrus' is the identical American spelling — choose by audience, not meaning. 'Heat', as in 'the dog is in heat', is the everyday informal word a pet owner or farmer would use for the same biological state, especially when talking about dogs, cats, or cattle. 'Rut', by contrast, refers to the seasonal mating period of male deer, elk, goats, and sheep, when the males fight and pursue females — so 'a stag in rut' and 'a doe in oestrus' describe two sides of the same event. Use 'oestrus' / 'estrus' in writing, 'heat' in speech, and 'rut' only of males.

oestrus ↗estrusheat ↗rut ↗

Common collocations

Nouns

  • oestrus cycle
  • oestrus period
  • oestrus detection
  • signs of oestrus

Phrases

  • come into oestrus
  • synchronise oestrus
  • induce oestrus

Prepositions

  • in oestrus
  • during oestrus

Etymology

GreekLatinEnglish

Borrowed into English in the 17th century from Latin 'oestrus' meaning 'gadfly' or 'frenzy', which in turn came from Greek 'oistros' — a word that named both the biting horsefly and the wild, driving passion the fly was thought to cause in cattle. The biological 'fertile period' meaning developed in the 19th century as scientists noticed how restless and driven mammals became during this stage of the reproductive cycle. The British spelling keeps the Latin 'oe-'; American English simplifies it to 'estrus'.