Reproductive Physiology and the Oestrus Cycle

These flashcards cover the definitions of puberty, types of reproductive cyclicity, and the physiological and endocrine phases of the oestrus cycle based on the lecture transcript.

Puberty

The point when an animal is able to start reproductive activity and is considered the first milestone in breeding.

Age at first heat

A definition of puberty based on when an animal demonstrates reproductive activity and readiness to be covered by a male.

Silent heats

Cycles occurring early in puberty where the animal produces hormones and shows behavioral changes but does not actually ovulate.

Age at first ovulation

A definition of puberty marking the first time an animal produces a mature egg capable of being fertilised.

Dairy cattle puberty age

Typically occurs between 7-12 months of age, below a year of age

Beef cattle puberty age

This typically occurs from $12\,\text{months}$ onwards.

Oestrus cycle

The actual cycle consisting of a series of recurring reproductive events controlled by reproductive hormones.

Oestrus

A specific period of sexual receptivity within the oestrus cycle, also known as heat.

Polyoestrus cycler

An animal that has regular oestrus cycles throughout the whole year.

Seasonally polyoestrous

An animal that has regular oestrous cycles but only during certain parts or seasons of the year.

Monoestrous

An animal that typically has only one oestrus cycle within a year.

Long day breeder

Seasonal breeders that breed in the springtime or summer when there are longer hours of light and shorter hours of dark.

Short day breeder

Seasonal breeders, such as the ewe, that breed in the autumn or winter when there are longer hours of dark and shorter hours of light.

Spontaneous ovulators

Animals that ovulate naturally at the appropriate point in their reproductive cycle.

Induced ovulators

Animals that require a specific stimulus, such as being covered by a male, to trigger ovulation.

Anoestrus

A period within an animal's life or cycle where there is no cyclicity.

Gestational anoestrus

A period without cyclicity that occurs because the animal is pregnant and must concentrate on developing the pregnancy.

Lactational anoestrus

A period where animals like the bitch, queen, ewe, and sow are unable to cycle while they are lactating and supporting young.

Foal heat

The first heat seen in a mare after parturition, which typically occurs up to around $2\,\text{weeks}$ later.

Post-parturition cycling in cattle

The period after giving birth before an animal starts cycling again, which in cattle is typically $30\,\text{days}$ to $60\,\text{days}$ onwards.

Diestrus

The period within an oestrus cycle where an animal is not sexually receptive.

Metoestrus

The transitional period where the hormones of diestrus start to increase and the hormones of oestrus begin to slough off.

Proestrus

The period where reproductive hormones start to ramp up leading into the oestrus period.

Estradiol

The main hormone of oestrus produced by the cells in the follicle.

Progesterone

The main hormone of diestrus produced by the corpus luteum, also abbreviated as $P_4$.

Follicular phase

The phase of the cycle following luteolysis characterized by follicle development and a peak in estradiol.

Luteal phase

The phase of the cycle occurring after ovulation when an active corpus luteum produces progesterone.

Luteolysis

The key physiological event from the previous cycle that defines the beginning of the follicular phase.

Ovulation

The physiological event that defines the beginning of the luteal phase.

GnRH

Gonadotropin releasing hormone; the kickstarter for the reproductive system produced by the hypothalamus.