Estrus and Menstruation

Estrus – Time of ovulation and sexual receptivity in most mammals; known as heat

Menstruation – the shedding of the thickened lining of the uterus in humans and some primates

Animals in estrus mate whenever with whomever when in estrus vs. animals with a menstrual cycle choose when and with whom to mate.

Cows 21 daysPigs 21 daysMares 21 daysEwes 16 days

The estrus cycle is the period of days between coming into “heat”

“Heat” is the term used to describe estrus or sexual receptivity in livestock

Estrus is brought on by a drop in progesterone levels and an increase in estrogen levels

Cows 12-24 hrsPigs 24-36 hrsMares 4 daysEwes 24 hrs

period following estrus when cattle and goats ovulate LH is released when the follicle

ruptures and stimulates the remaining follicle tissue to form the Corpus Luteum

Corpus Luteum produces progesterone which maintains pregnancy

period when the system assumes pregnancy

longest phase of estrus cycle

If pregnancy is not established the CL begins to regress

Progesterone levels dropThe body prepares for estrus again

Day 1 – first day of menstruationDay 5 – Last day of menstruationDay 14 – Ovulation ** Unpredictability of human body

Time at which animals reach a level of sexual maturity that will sustain reproduction

Not best time to breed animal, not fully mature

Cows 1-1½ yearsPigs 5-10 moHorses 1½-2 years

Cows 2-2½ yearsPigs 1-1½ yearsHorses 2½-3 years