Gestation (Average Length Of Pregnancy)   Horses: Heavy (Draft) The normal is 330 to 340 days.                  Light (Riding)  The normal is 340 to 342 days.     Donkey:  The normal is 365 days.    Dog:  The normal is 59 to 66 days    Dog:  58 to 70 days noted in rare occurrences.   Cat:  The normal is 58 to 65 days   Reproductive Cycles (Average)   Horse: Cycle Length:  Normal is 21 days.  Can vary from 19 to 26.              Duration of Estrus: Normal is first 6 days of cycle.              Can vary from 2 to 10 days.              Best breeding Time: Early on 3rd day, then every 2nd day,              until the mare refuses to accept the stallion.   Dog:  Cycle Length:  Normal is 21 days.            Duration of Estrus: From day 10 of her cycle until the female            no longer stands for the male.            Best breeding Time:  day 10, 12, 14, continuing until               the female no longer accepts the male "Willingly".   Cat:  Cycle Length:  14 to 21 days.           Duration of Estrus:  Normal is 6 to 7 days during her cycle.           Best breeding time:  Daily from day 2 of Estrus.  Until           the female no longer accepts the male.