Regulation and Function of Gonadotropins Throughout the Bovine Oestrous Cycle

Gonadotropins are protein hormones secreted by the pituitary gland and include luteinizing hormone (LH) and follicle stimulating hormone (FSH). Both LH and FSH govern the estrous cycle i.e. the cyclical pattern of ovarian activity that facilitates the transition of female animals between periods of reproductive non-receptivity to receptivity enabling mating and subsequent pregnancy. The onset of estrous cycles occurs at the time of puberty. In heifers puberty occurs at 6–12 months of age, generally at a weight of 200–250 kg. The normal duration of an estrous cycle in cattle is 18–24 days. The cycle consists of two discrete phases: the luteal phase (14–18 days) and the follicular phase (4–6 days). The luteal phase is the period following ovulation when the corpus luteum (CL) is formed (often further designated as metestrus and diestrus), while the follicular phase is the period following the demise of the corpus luteum (luteolysis) until ovulation (often further designated as pro-oestrus and oestrus). During the follicular phase, final maturation and ovulation of the ovulatory follicle occurs, the oocyte is released into the oviduct allowing the potential for fertilization.