Prostaglandins induce heat within 72 hours if a functional CL3 is present. If there is no CL3, expect no response. If the ovary has a CL2 or CL1, the dominant follicle begins estrus within 5 days. The interval from injection to estrus is 2.5 days for heifers and 2.5-5 days for cows. Conception rates are lower if a single insemination straw is used after prostaglandins have been given.
Double straws are better.
The release pattern of GnRH from the hypothalamus is influenced by the nutritional intake of the cow. Also adequate dietary vitamin A and protein are needed to maintain body condition and steroid production. Conscientious owners understand their herd's estrous cycles through continuous observation and scheduled palpation. A proper interval should be provided for uterine involution. Cows less than 50 days after calving should not be bred without a thorough reproductive examination.