kiertoestrus

Kiertoestrus, commonly translated as cycling estrus, refers to the normal, recurring pattern of reproductive cycling in sexually mature female mammals that are capable of ovulation. It describes repeated estrous cycles in the absence of pregnancy and is characteristic of polyestrous and some seasonally polyestrous species. The term distinguishes cyclic estrous activity from irregular or absent cycling (anestrus).

Physiology and phases: The cycle is governed by the hypothalamic–pituitary–gonadal axis. Gonadotropin-releasing hormone (GnRH) stimulates the pituitary to release LH and FSH, which promote ovarian follicle development and estrogen production. Rising estrogen triggers estrus, the period of sexual receptivity. Ovulation often follows estrus, after which the corpus luteum forms and secretes progesterone. If the animal does not become pregnant, luteolysis resets the cycle. The cycle is divided into phases—proestrus (follicular development and rising estrogen), estrus (receptivity and ovulation in many species), metestrus (early luteal phase), and diestrus (the luteal phase with progesterone predominance). Duration and presentation of these phases vary by species.

Occurrence and variation: Cycle length varies among species, commonly ranging from about 17 to 24 days in many farm animals, with shorter or longer intervals in others. The clinical signs of estrus and the exact timing of ovulation are species-specific, and some animals may display subtler cues than others.

Diagnosis and management: Detecting estrus relies on behavioral and physical signs, sometimes aided by veterinary tools or hormone testing. Breeding management may include estrus synchronization using hormones (such as prostaglandins, GnRH, or progestogens) to optimize timing for conception or artificial insemination. Proper recognition of kiertoestrus supports reproductive efficiency and welfare.