Reproductive Hormones and Puberty in Animals

Follicular Phase

The phase consisting of Proestrus and Estrus, where FSH selects a follicle.

Proestrus

A new beginning where if pregnancy occurs, proestrus does not happen, and the number of follicles is set.

Follicle Stimulating Hormone (FSH)

A hormone that promotes follicle growth and is stimulated by Activins released from follicles.

Estrus

The phase where Estradiol induces heat behaviors, prepares the reproductive tract, triggers the LH peak, activates sexual behavior, and mucus is produced, culminating in ovulation.

Luteal Phase

The phase consisting of Metaestrus and Diestrus, characterized by the formation of the corpus luteum.

Metaestrus

The beginning of corpus luteum formation, where it secretes Progesterone that inhibits GnRH.

Diestrus

The phase where the corpus luteum is mature, maintains high Progesterone levels, and if pregnancy does not occur, Prostaglandin F2 alpha is released to destroy the corpus luteum.

Luteinizing Hormone (LH)

A hormone that peaks during Estrus, triggered by Estradiol.

Negative Feedback Mechanisms

Regulatory processes that ensure LH and FSH do not peak at the same time, helping to time ovulation.

Frisch Theory

The theory that the onset of puberty is related to body mass index (BMI), beginning when an animal reaches a certain threshold of body fat.

Leptin

A hormone produced by fat cells that plays a key role in triggering puberty.

Internal Factors Influencing Puberty

Factors such as Genotype, Liveweight, Body Condition, and Age that impact the timing of puberty.

External Factors Influencing Puberty

Factors such as Environment, Photoperiod, Nutrition, and Socio-Sexual Interactions that can affect puberty timing.

Genotype

The genetic makeup that impacts puberty timing across species.

Milk Type Females

Females that are milked may reach puberty earlier due to better body condition and nutritional support.

Body Condition

The percentage of body fat that is critical for initiating puberty.

Age

Older animals may reach puberty sooner, provided they have sufficient body mass.

Nutrition

Adequate nutrition, especially fat reserves, is vital for the onset of puberty.

Photoperiod (Day Length)

Longer days may accelerate puberty, while shorter days may delay it.

Socio-Sexual Interactions

Exposure to males or other females can influence the timing of puberty.

Progesterone

A hormone secreted by the corpus luteum that inhibits gonadotropin release and prevents ovulation.

Prostaglandin F2 alpha

A substance released by the endometrium to destroy the corpus luteum if pregnancy does not occur.

Genetic Variability

Muscle Depth and Fat Depth: These can impact how quickly animals reach puberty, as fat reserves and body condition are important for leptin production and hormonal signaling.

What is Weight?

Body weight is a key indicator of an animal's nutritional status and fat reserves, directly impacting the onset of puberty.

Singles vs. Twins vs. Triplets

Animals born in litters (twins or triplets) may experience delayed puberty compared to singletons due to reduced access to nutrients in the womb, affecting body weight and fat reserves at birth.

Negative Energy Balance

If an animal is in a state where it's not getting enough energy (either through poor nutrition or illness), puberty may be delayed.

Decreased Quantity or Quality of Food

Lack of essential nutrients delays puberty because growth factors (like leptin) are insufficient to trigger hormonal changes.

Not Enough Growth Factors

Insufficient growth factors like leptin can delay the onset of puberty.

Puberty and Socio-Sexual Interactions

Exposure to male animals or other females can influence puberty timing.

Confounding Factor

It's important to separate socio-sexual interactions from other factors like body weight when studying puberty.

Breeding Seasonality

Animals often breed in certain seasons, influenced by photoperiod (light/dark cycle) and melatonin (a hormone triggered by darkness).

Modulating Factors

Body Weight, Condition, Genotype: These factors also play a role in reproductive timing.

Manipulating Breeding Seasons

Night Duration: Shorter or longer nights can impact reproductive cycles.

Melatonin Implants

These can artificially alter the reproductive season.

Progestogens/Progestagens

Hormonal treatments to control estrous cycles.

GnRh

GONADOTROPINE LIBERATING HORMONE: Stimulates the production and release of FSH and LH, by the anterior pituitary gland (anterior lobe of the pituitary gland).

FSH

It stimulates the growth and maturation of the follicles that are found in the ovary.

LH

It contributes to the last phase of maturation of the follicle (which has become dominant) and to trigger its ovulation.

Estradiol

Contributes to expressing sexual behavior (behavior characteristic of heat or heat) in the female, by acting on the central nervous system.

Inhibit

Inhibits the release of FSH without altering the release of LH.

Progesterone

It inhibits the release of GnRh, which will also decrease the levels of FSH and LH. This prevents new ovulations.

PGF2a

Causes regression or destruction of the corpus luteum (promotes luteolysis).