1 department of veterinary reproduction faculty of veterinary medicine airlangga university 2009...

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Department of Veterinary ReproductionFaculty of Veterinary Medicine

Airlangga University 2009

PHYSIOLOGY OF REPRODUCTIONREPRODUCTIVE CYCLES

Part I

ByDr. Abdul samik, M.Si.,Drh

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The Reproduction Cycles

Phenomena : • Puberty and sexual maturity• The breeding season• The estrous cycle• Postpartum sexual activity• Aging and fertility



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Regulation of Reproductive Cycle

• Environmental• Genetic• Physiologic• Hormonal• Behavioral• Psychosocial



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Events of Reproduction• Puberty- Age at which reproductive organs become

functional• Female- Reproduction process occurs within

– Estrous cycle- Repetitive cycle occurring when pregnancy does not

– Estrus- “Heat” or receptivity to mating• Fertilization- Egg & Sperm unite

– Only real male contribution is the sperm• Gestation- Length of time of pregnancy• Parturition- Act of giving birth



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Age of Puberty

• Cattle: 6 to 12 Months• Sheep: 5 to 7 Months• Swine: 4 to 8 Months• Horses: 12 to 15 Months• Humans: 9 to 16 Years



Puberty in Heifers

• Physiological events leading up to puberty• Endocrine and morphological events in

peripubertal heifers are similar to the resumption of cyclicity post partum in mature cows.

• Decreased negative feedback of oestradiol • Maturation of the hypothalamus • Increased frequency of release of LH pulses • Enhanced development of ovarian follicles • Enough oestradiol produced to induce

behavioural oestrus and a preovulatory surge of gonadotrophins

• Puberty is attained with the first behavioural oestrus that is accompanied by ovulation and development of a corpus luteum with a typical life span

• What influences the onset of puberty in heifers?

• Factors that can influence the pubertal rise in release of LH pulses are:

• genotype • season of year when pubertal age is

attained • growth or nutritional intake • social cues • treatment with exogenous hormones

Endocrine mechanisms of puberty

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The Estrus Cycle

• When Heifer becomes sexually mature• ovaries function in a cycle activity• estrus period cycle 17-24 days (21 days)

Estrous cycle – period of time from one estrus to the next



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Breeding Season• Monoestrous : dog, cat• Polyestrous (cycle throughout year) : cattle,

goat, sheep, swine• Seasonal polyestrous (Decreasing light, Fall) :

sheep, goat• Seasonal polyestrus (Increasing daylight,

Spring) : horse



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Length of Estrus Cycle

• Cattle: 19 to 23 Days• Sheep: 14 to 19 Days• Swine: 19 to 23 Days• Horses: 10 to 37 Days



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Duration of Estrus Phase

• Cattle: 6 to 27 Hours• Sheep: 24 to 36 Hours• Swine: 48 to 72 Hours• Horses: 3 to 8 Days



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Luteal phase.

A corpus luteum is formed under the influence of pituitary LH. The function of the corpus luteum is to secrete progesterone, which reduces the amount of the hormone oestrogen produced. As long as the corpus luteum is functional, oestrogen is unable to trigger formation of the follicle (a large fluid-filled sac containing the egg). By day 18 the corpus luteum degenerates due to prostaglandin (released from the uterus) and goes through a regression phase. Associated with corpus luteum regression is a decline in progesterone

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Follicular phase

Following the decline in progesterone, an increase in oestrogen (mainly oestradiol-17β) takes place and peaks before the onset of oestrus.

Oestrogen stimulates the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus.

GnRH stimulates the release of FSH and LH from the pituitary gland. LH rises to a peak at the beginning of oestrus. FSH and LH stimulate the

development of follicles in the ovary.



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One follicle predominates which secretes oestrogen and triggers a wide range of anatomical and physiological changes in the cow

All the changes ensure that if the cow is mated, the sperm will stay alive until one of the spermatozoa will effect fertilisation.

The follicle ruptures and releases the egg (ovulation).



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Stage of heatStage of heat

ProestrusProestrus EstrusEstrus

Metestrus Metestrus DiestrusDiestrus



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Stage of heatA. Proestrus• day 19 -21• period for preparation of

sexual activity



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Stage of heatB. Estrus (heat, sexual

desire)• period of sexual activity,

female permit mating• duration : 6 - 30 hrs

(heifer 15, cows 18hrs)



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Signs of Estrus

• Primary Sign of Estrus

– Stands immobile when mounted.



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Secondary Signs of Estrus• Behavioral

– Bellowing– Increased Activity– Walking the fence line– Charging– Butting– Licking

– Sniffing– Flehmen posture

(inverted nostrils)– Circling– Chin-resting– Mounting



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• Physical Signs of Estrus

– Manure on flanks– Roughened tailhead– Loss of hair on tailhead– Abrasions on tailhead

– Red vulva– Swollen vulva– Clear mucus

discharge from vulva



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• Miscellaneous Signs of Estrus

– Depressed appetite– Depressed milk production– Frequent Urination– Metestrus bleeding : 35-45 hours

after estrus; too late to breed



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Stage of heatC. Metestrus (after heat)• day 1-5 of cycle• not permit mounting• 50% cow , 90% heifer -

metestral bleeding• corpus luteum begins to

develop



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Stage of heatD. Diestrus (between heat)• day 5 - 19• complete lack of sexual

desire



Estrous Cycle

0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 0 1

Hor

mon

e Le

vel

Progesterone (P4)

Estradiol (E2)

Day of Estrous Cycle

New CLForming

Mature CL Present Fol. Size

& CL Size

LH and FSH During the Estrous CycleH

o rm

one

Con

cen t

r at i

o n

Days Relative to EstrusEstrus Estrus5 10 15

Progesterone

FSH

LH

The Estrous Cycle in CattleH

o rm

one

Con

cen t

r at i

o n

Days Relative to EstrusEstrus Estrus5 10 15

1st

Wave2nd

WaveProgesterone

EstradiolFSH

LH

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Mechanisms of luteolysis during the oestrus cycle of cowsLuteolysis starts between days 16-17 post oestrus in the cow. Bovine luteal tissue is

usually not responsive to PGF2-alpha until after day 4 post oestrus

Two major mechanisms of luteolysis have been suggested:

1. Reduction of the blood flow in the corpus luteum (CL)A rapid decrease in luteal blood flow has been recently proposed as one of the main luteolytic actions of PGF2-alpha. It was demonstrated that the reduction in luteal blood supply 8 hours after prostaglandin injection was coincident with the onset of structural luteolysis, the first significant decrease in CL volume was seen.



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2. Direct action on luteal cells

A direct action of prostaglandin on the luteal cells, resulting from both the

decrease in cAMP synthesis normally produced in response to LH and the

inhibition of the steroidogenic action of cAMP. These effects would be further

amplified by a reduction in the number of receptors for LH.

This theory is further supported by the result of a study that demonstrated that

a prostaglandin-induced decrease in plasma progesterone concentrations

occurs before a detectable decrease in both the volume of the CL and the

luteal blood flow.



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Follicular development in cattle

Ovarian follicular growth and development in ruminants is characterised by

two or three consecutive follicular waves per oestrous cycle.

Each wave involves the recruitment of a cohort of follicles and the selection of

a dominant follicle.

The dominant follicle continues to grow and mature to the preovulatory stage

while others undergo atresia.



Hor

mon

e Le

vel

P4

E2

Ovulation

Attretic (Die)OvarianFollicularPool

Follicular Waves

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Recruitment of follicular waves

The growth of follicular waves is initiated by a rise in circulating FSH.

All follicles growing as a cohort contain specific receptors for FSH and

depend on this gonadotrophin in their growth.

At this stage the growing follicles do not have a sufficient population of

LH receptors to respond to a LH-like stimulation.

For this reason this stage of follicular growth is sometimes called FSH-

dependent.



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For reasons not yet properly understood only one dominant follicle is selected

from among the cohort recruited by the small rise in FSH. A defining

characteristic of the dominant follicle appears to be its greater capacity for

estradiol production.

Selection of the dominant follicle is associated with a decrease in FSH, FSH is

maintained at basal levels. The selected future dominant follicle acquires LH

receptors which allow it to continue growth in the environment of low FSH and

increasing LH levels.



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It seems that by decreasing the FSH support, the selected follicle depletes

subordinate follicles from their vital growth stimulant while it benefits from

both the low FSH and growing LH stimulation



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Selected dominant follicle and ovulation

Following its selection, DF growth, oestrogen activity and lifespan are

controlled by the LH pulse pattern. In response to maximum concentrations

of oestrogens produced by the dominant follicle a massive LH release takes

place. It is called a pre-ovulatory LH surge or peak and acts as the direct

stimulation of ovulation



1 department of veterinary reproduction faculty of veterinary medicine airlangga university 2009...

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