The breeding cycle of cattle

The cow is a continual-type, polyoestral species with an average cycle length of 21/22 days for previously bred cows and 20 days for heifers. Sexual activity starts at puberty, when the animal has reached 40 to 45% of its adult weight, and then follows a cyclic pattern, characterised by the periodic onset of oestrus. Oestrus, when the animal is “on heat”, is the time when the male is accepted and mounting occurs. This period coincides with the presence of a mature Graafian follicle in the ovary, which is later released by ovulation. Oestrus lasts for 6 to 30 hours and is characterised by visible signs: excitation, anxiety, bellowing, inciting mounting behaviour from other animals and passive acceptation of being mounted by a bull or another cow, in addition to increased vaginal mucus. Ovulation occurs 6 to 14 hours after the end of oestrus and is followed by the formation of the corpus luteum and the start of a period when the uterus becomes gravid, corresponding to the time when the luteal function is active.