Estrous cycle
Estrous cycle can be defined as cyclic period of sexual receptivity exhibited by the females at regular intervals.
Estrous cycle is controlled directly by hormones of the ovary and indirectly by the hormones of the adenohypophysis. The basic pattern of the cycle is same but species differences are found in different stages of the cycle.
In all domestic animals that have attained puberty there is a definite physiological functional rhythm of the reproductive system called the estrous cycle. One cycle interval is defined as the time from the onset of one period of sexual receptivity to the next or as the interval between successive estrus.
Monoestrus animals have only one estrous cycle per year like dogs, wolves, bears but polyestrus animals have several estrous cycles per year like cattle, pigs, human.
Seasonal breeders are animals that have one or more estrous cycles during certain periods of the year. Seasonally polyestrous animals (exhibit many cycles of estrous during certain periods of the year known as breeding season)like ewes, does and mares.
Cows and sows are non-seasonally polyestrous animals.
Seasonally monoestrus animal is (exhibit a single estrus followed by anestrus ) bitches or female dogs.
The queen will undergo a series of ovulatory estrus in each breeding season in spring, summer and early autumn.
Different phases of estrous cycle
The estrous cycle is divided into four marked phases-
Based on changes occurring in the ovary, estrous cycle consists of Follicular phase and Luteal phase.
- Follicular phase – also known as proliferative or oestrogenic phase – oocyte matures, ovulation occurs, estradiol from the follicle is dominant – includes proestrus and estrus phases
- Luteal phase (secretory phase) – corpus luteum forms, fertilization and embryo development, progesterone from the CL is dominant – includes metestrus and diestrus