Reproduction, Events and Management: Estrous Cycles: Characteristics

Abstract

The estrous cycle in cattle lasts for 18–24 days. It consists of a luteal phase (14–18 days) and a follicular phase (4–6 days). During the cycle there are generally 2 (dairy cows) or 3 (heifers and beef cows) waves of ovarian follicle growth. Each wave of follicle growth consists of a period of emergence of a cohort of follicles, selection of a dominant follicle and either atresia or ovulation of the dominant follicle. These waves of follicle growth occur throughout the entire cycle, with only the dominant follicle of the final wave coinciding with the follicular phase that undergoes final maturation and ovulation. Ovarian function (follicle growth, ovulation, luteinization and luteolysis) are regulated by the endocrine hormones of the hypothalamus (gonadotropin-releasing hormone), anterior pituitary (follicle-stimulating hormone and luteinizing hormone), ovaries (progesterone, estradiol and inhibins) and the uterus (prostaglandin F2α).