The Estrous cycle of cow ranges 17-24 days in duration.
Each cycle consists of a long luteal phase 1-17th day.In luteal phase the cycle is under the influence of progestiron harmone.
After that there is a shorter folicular phase.In this phase cycle is under the influence of Estrogen harmone.
Next is the Estrous phase.In this phase the secretion of Estrogen reaches to maximum.The time duration of this phase is 6-24 hours.During this time animal shows heat symptoms.Ovulation occour between 24th-32nd hour of onset of Estrous.The average life of egg is 48 hours after ovulation.So one must weight for 48 hours after heat symptoms.
The best time for insemination is 48th-60th hour after the onset of heat symptoms.