Question

Identify from the following group animals which exhibit oestrous cycle
(a) Lion, deer, dog and cow
(b) Cow, monkey, elephant and ape
(c) Monkey, ape, man and elephant
(d) Lion, dog, monkey and ape

Answer 1

Hint: Oestrous cycle is seen in animals belonging to the group of non-primate vertebrates. The first one among them include females with polyoestrous cycles. The oestrous cycle in the second kind of animal varies from 17 to 22 days. The third animal included in this group usually is diestrous. This cycle starts around 12 months of age in the fourth kind of animal.

Complete step by step answer:
From the given group animals the ones which exhibit oestrous cycle are lion, deer, dog and cow.
Let's begin the explanation by learning about types of the reproductive cycle in animals.
The two types of reproductive cycles recognised in animals are estrual and menstrual, with the term ‘ovarian cycle’ representing the interval between two successive ovulations. The term oestrous is derived from the Latin word ‘oestrus’, meaning frenzy. The set of recurring physiological events that are induced by reproductive hormones in most of the mammalian therian females is called ‘estrous cycle’ or ‘oestrous cycle.’ This cycle starts after sexual maturity in females but is interrupted by anestrous phase or by pregnancies. The gap between two oestrous periods constitutes an oestrous cycle. Typically oestrous cycles in females continue until death. A four- phase terminology can be used in reference to animals exhibiting oestrous cycle. They are proestrus, estrus, metestrus or diestrus and anestrus. Some animals may also display blood discharge from vagina often mistaken for menstruation. There are a variety of different oestrus forms:
Polyestrous animals:Oestrous cycles in these animals are seen throughout the year. Examples are cattle lioness, pigs, mouse rats etc.
Seasonally polyestrous animals:Some animals have multiple oestrous cycles only during certain periods of the year, for example, horses, sheep, cats, deer, goats etc.
Monestrous animals:Animals in which one oestrous cycle occurs per year are said to be monestrous. Examples being wolves, bears and foxes.
So, the correct answer is, ‘Lion, deer, dog and cow.’

Additional information:
- The duration of the oestrous cycle in deer is 17 to 22 days.
- A female dog usually goes into heat typically twice a year so dogs are diestrous.
- In cows, the oestrous cycle is a balance between progesterone and oestrogen with females coming into heat every 21 days until pregnant.

Note:
- Animals that show oestrous cycle resorb the endometrium if conception does not occur during that cycle while animals that present with menstrual cycles shed the endometrium through menstruation.
- Monkeys, apes and man are primate vertebrates exhibiting menstrual cycle instead of oestrus.
- Elephants exhibit the longest oestrous cycle amongst all studied non- seasonal mammals to date. It varies from 13 to 18 weeks.