Glossary
Veterinary Reproduction Terms: Estrus, Anestrus, Polyestrous, Induced Ovulator, Silent Heat and More
Terms used to describe the reproductive cycle of domestic animals. Each definition is quoted or closely paraphrased from the cited source, and each example uses that source's own figures.
Reproduction terms (20)
| Term | Definition | Example |
|---|---|---|
| Estrous cycle | The period from one estrus (heat, the phase of sexual receptivity) to the next estrus [1]. | Cattle: 21 days (18–24) [3]. |
| Estrus (heat) | The phase of sexual receptivity [1]. | Cattle: 18 h (6–24); mare: 5–7 days [3]. |
| Standing estrus (standing heat) | A brief period within a female's estrous cycle during which she will allow herself to be mounted [2]. | Standing still while another animal attempts to mount is the only definitive sign of estrus in cattle [2]. |
| Anestrus (acyclic) | Periods when a cow or heifer does not display estrous cycles are called anestrous or acyclic [1]. | |
| Ovulation | The rupturing of the follicle that releases the ovum (egg) [1]. | Cattle: 10–12 h after the end of estrus [3]. |
| Corpus luteum (CL) | The structure the ovulated follicle turns into — by approximately day 5 of the estrous cycle in cattle [1]. | In cattle, prostaglandin F2α lyses the CL around day 17 and it regresses in about three to five days [1]. |
| Luteal phase | The part of the estrous cycle controlled by the corpus luteum [6]. | Mare: the luteal phase controls the largest portion of the cycle, with approximately 14 days dedicated to the CL [6]. |
| Polyestrous | Having repeated estrous cycles; "polyestrous all year" means cycling throughout the year. | Cattle and pigs are polyestrous all year [3]. |
| Seasonally polyestrous | Having repeated estrous cycles only during a breeding season. | Sheep (early autumn to winter), goats, horses and cats are seasonally polyestrous [3]. |
| Monestrous | Having one estrous cycle per breeding season or per year, rather than repeated cycles. | The bitch is monestrous all year, with cycles 6–7 months apart [3]. |
| Short-day breeder | An animal whose breeding season is triggered by shortening days [5]. | Most sheep are seasonally polyestrous and short-day breeders [5]. |
| Long-day breeder | An animal that cycles when days are long; the seasonality of the mare's cycle is mostly dictated by photoperiod [6]. | Mares are long-day breeders [6]. |
| Induced ovulation (induced ovulator) | Ovulation that is triggered by mating rather than occurring spontaneously [3][7]. | In the cat, ovulation is induced by vaginal-cervical stimulation and occurs 24–48 h after breeding [3][7]; alpacas are induced ovulators [3]. |
| Silent heat (silent ovulation) | Ovulation without overt estrus behaviour [4]. | About 63% of buffaloes had silent ovulations during the postpartum period [4]; some mares show silent heat with a foal at side or with improper body condition [6]. |
| Ram effect (male effect) | The stimulation of non-cycling ewes to ovulate by the sudden introduction of an intact male or a vasectomized (teaser) ram [5]. | |
| Foal heat | The first estrus after foaling [3]. | Occurs at 9 days (4–14) after parturition [3]. |
| Proestrus bleeding | Serosanguineous vulvar discharge in the bitch during proestrus, the phase that precedes estrus. | Lasts 7–10 days [3]. |
| Pseudopregnancy | A luteal phase without pregnancy, which in some species produces signs resembling pregnancy. | In the cat — for example after a sterile mating — pseudopregnancy lasts 40 days [3]. |
| Back-pressure test | A test of estrus in the gilt or sow: a positive response to pressure on the back, like standing to the boar, is the ultimate criterion of estrus [8]. | |
| Gestation | The period between fertilization and parturition [1]. | Gestation lengths for each species are on the reproduction pages. |
Frequently asked questions
What is the difference between polyestrous and seasonally polyestrous?
Polyestrous animals such as cattle and pigs cycle repeatedly all year; seasonally polyestrous animals such as sheep, goats, horses and cats cycle repeatedly only during a breeding season [3].
What is an induced ovulator?
Related tools and references
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Ask WeVet about thisReferences
- The Estrous Cycle of Cattle (Publication 2616)
- Standing estrus (heat) and heat detection aids in cattle
- Features of the Reproductive Cycle (table)
- Estrus Detection in Buffaloes (Bubaline Theriogenology)
- Reproduction in the ewe (Sheep 201)
- Understanding Reproductive Events in the Mare for Successful Breeding Programs (Bulletin 1434)
- Breeding Management of Queens
- Breeding Management of Pigs
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