41. He is testing for when the female enters estrus , which is when mating begins. 42. Dogs do not experience menopause; the canine estrus cycle simply becomes irregular and infrequent. 43. They will prevent a ewe from accessing tending areas before she even goes into estrus . 44. Another important physiological change related to sexuality in humans was the evolution of hidden estrus . 45. Some fillies may exhibit estrus as yearlings. 46. When females go into estrus aggressiveness increases. 47. Reproduction is seasonal, with gestation lasting 5 6 months and estrus lasting 4 months. 48. It was released in 1997 on Estrus . 49. Usually a system of synchronized estrus , pregnancy and births produces cubs of the same age. 50. Most importantly, during estrus she will stand still when mounted by another cow or bull.
