11. :: Cows have a 21 day Estrous cycle . 12. One signal is released during the follicular phase of the estrous cycle and it shortens estrous cycles. 13. One signal is released during the follicular phase of the estrous cycle and it shortens estrous cycles . 14. Typically, estrous cycles continue until death. 15. This mutual lengthening and shortening of estrous cycles was theorized to produce synchronization of estrous cycles over time. 16. The second signal is released during the ovulatory phase of the estrous cycle and it lengthens estrous cycles. 17. This mutual lengthening and shortening of estrous cycles was theorized to produce synchronization of estrous cycles over time. 18. Indeed, ovandrotone albumin has been found to significantly increase luteinizing hormone levels throughout the estrous cycle in ewes. 19. The second signal is released during the ovulatory phase of the estrous cycle and it lengthens estrous cycles . 20. Humans do not display their estrous cycle externally and like Bonobos use sex for social reasons unrelated to procreation.
