Oestrous Cycle        Menstrual Cycle Occurs in non-primates. Occurs in primates only.  There is estrus/heat production at the time of ovulation and copulation occurs only during that period.  There is no heat period and copulation occurs during any time of the cycle. The broken endometrium is reabsorbed. The broken endometrium is passed out during menstruation. Examples- cow, sheep, rat, deer, dog, tiger, etc Examples: monkeys, apes and human beings