Question

classify the animals in terms of the type of estrus they indicate

Answer 1

Estrus is the phase when the female is sexually receptive. It is also referred to as heat period. Estrus cycle is the main reproductive cycle of non primate vertebrates like rat, mice, pigs etc. The estrus cycle has 4 distinct phases which include  proestrus, estrus, metestrus, and diestrus. During proestrus phase follicle enlarges, estrogen hormone increases, vascularity of reproductive tract increases and endometrial gland begin to grow. In Estrus phase the female is receptive and the female allows the male to mount. Estrogen levels decline and LH surge is seen. Ovulation occurs 24 to 48 hours after surge. Uterine motility is high with optimal transport of sperm. Also cervical mucus increases. In metestrus, estrogen levels are low and uterine contraction subside. Endometrial gland continues to grow. In cattle bleeding occurs.FSH increase triggering growth of follicles. In diestrus, progesterone is high. Contraction stops and the corpus luteum regresses at the end of this period if female is not pregnant.

Bases on the periodicity of the cycle, animals can be classified as follows:

• Polyestrous Animals - They have estrous cycles throughout the year (cattle, pigs, mice, rats).
• Seasonally Polyestrous Animals - Animals that have multiple estrous cycles only during certain periods of the year (horses, sheep, goats, deer, cats).
• Monestrous Animals - Animals that have only one estrous cycle per year (dogs, wolves, foxes, and bear)

Anestrus is not a phase of the cycle but a prolonged period of reproductive rest or quiescent.