Equine reproductive physiology

what type of oestrus cycle does a mare have?

seasonal polyoestrous

what does seasonal polyoestrous mean?

multiple cycles during one season

what causes cycling in mares and so when is there season?

long days cause cycling and season is April to August usually

what are the three stages of the oestrus cycle?

anoestrus
transition phase
cycling

what occurs during anoestrous?

not cycling, winter months and ovaries are dormant

when does the transition phase occur?

50-70 days prior to first ovulation

what are the two stages in cycling?

dioestrus - 16 days
oestrus - 5 days

how does light affect oestrous?

• light detected by eye which then goes to the pineal gland

• this activates brain centres

• decreased melatonin secretion with decreasing periods of dark

• release of gonadotropins (FSH and LH)

• activates ovary, which stimulates the development of follicles

• Follicles then produce progesterone and oestrogen

• influences behaviour and receptivity

• changes the uterine environment to produce eggs and allow fertilisation to occur
  

what hormones do follicles release?

oestrogen and progesterone

what does the release of oestrogen and progesterone from follicles cause?

influences behaviour and receptivity of mare
alters uterine environment to produce eggs and allow fertilisation to occur

ways to manipulate seasonality of mares and stallions?

• artificial change to photoperiod by putting mares and stallions under light during winter months

• physical change to photoperiod by moving mares and stallions from northern to southern hemisphere biannually

what occurs in oestrus?

luteolysis, follicular phase and oestrogen increase

what happens in dioestrus?

luteal phase, high progesterone

how long is dioestrus and what are the hormone levels?

16 days with high progesterone levels

why is dioestrus the luteal phase?

there is a CL on the ovary

how long is oestrus and what are the hormone levels?

5 days and high oestrogen

why is oestrous the luteolysis phase?

CL is removed and multiple follicles are produced

what does O stand for?

ovary

what does UH stand for?

uterine horns

what does BL stand for?

broad ligament

what does EUB stand for?

external uterine body

what does OD stand for?

oviduct

what does UtB stand for?

uterine body

what does CX stand for?

cervix

what does UB stand for?

urinary bladder

what does CV stand for?

cervical canal

what does Ve and Vu stand for?

vestibule and vulva

what does L and C stand for?

labia and clitoris

what is the clitoris a key area for with disease control?

key sampling point for venereal pathogen screening prior to breeding

what happens between day 2-6 with follicles?

multiple follicles form due to the 1st FSH peak

what happens to follicles between day 8-12?

follicles grow due to 2nd FSH peak

what happens to follicles day 16-18?

dominant follicle grows at a faster rate and the other follicles begin to regress

what happens at day 21?

follicle lysis and ovulation occurs due to LH

explain what is happening to the follicles at each stage

day 2-6 multiple follicles have formed due to 1st FSH peak
day 8-12 follciles are growing due to 2nd FSH peak
day 16-18 the dominant follicles grow faster and the other begin to regress
day 21 follicle lysis and ovulation due to LH

what does ovulation occur via?

ovulation fossa

what happens when the follicle ovulates?

oocyte is released
captured by fimbria of infundibulum
enters oviduct

what happens to the development of an egg if fertilisation occurs?

the fertilised embryo/egg enters uterus and develops

what happens to the egg if it is not fertilised?

oocyte degenerates in oviduct

what happens to the follicle post ovulation?

day 1-4 the ruptured follicle fills with blood and becomes corpus haemorrhagicum
day6-10 it differentiates into corpus luteum and secretes progesterone

when the CL is secreting progesterone which phase is this?

dioestrus/luteal phase

how does the CL secrete progesterone?

consists of luteal cells which secrete the progesterone

what is the definition of a CL?

soft tissue structure which releases progesterone and maintains pregnancy

what happens to CL if pregnant or not pregnant?

pregnant = CL remains

not pregnant = CL lysed by prostaglandin F2alpha

what does progesterone levels indicate the presence of?

a CL

what happens to the levels of progesterone after ovulation in mares?

rises rapidly

what is progesterone useful for measuring?

stage of cycle/ovulation

what else can be used alongside progesterone levels to monitor mares oestrus cycle?

palpation and ultrasound examination of the ovaries per rectum

what does <0 levels of progesterone show?

no CL and oestrus/anoestrus stage

what does 2.5 level of progesterone show?

CL present and dioestrus (early/late)

what does level 20 of progesterone show?

CL present and dioestrus

how do you monitor the levels of progesterone in the blood?

ELISA

when does true implantation occur?

at day 35

what happens with true implantation?

conceptus held stationary within uterine wall
sustains conceptus for remainder of gestation

what happens to the mares immune system at true implantation?

maternal immunological recognition of pregnancy
no longer seen as foreign body and prevents abortion

what is the allantochorion?

definitive placenta which sustains foetus
gas exchange occurs

what is the amnion?

surrounds foetus
poorly vascularised

what is the umbilicus?

connects allantochorion placenta to foetus

where does gas exchange happen between mother and foetus?

gas exchange and nutrient exchange occurs at the allantochorion interface with endometrium

what happens after gas exchange?

blood is then transported from the periphery of the placenta to the umbilical cord where it enter the foetus

how does oxygenated and deoxygenated blood enter and exit the foetus?

oxygen rich blood enter via umbilical vein and CO2 rich blood leaves via umbilical arteries

how does nutrient exchange vary between other animals and mares?

in other animals they have cotyledons whereas horses have micro cotyledons

what do mature endometrial cups secrete?

equine chorionic gonadotropins (eCG)/ pregnant mare serum gonadotropin (PMSG)

when are micro cotyledons fully present?

day 150-term

how are micro cotyledons present on the placenta?

they are diffusive across the whole outer layer

what stimulates parturition?

foetal hormonal signals

what are the three stages of parturition?

1. initiation of myometrial contractions 1-4 hours

2. expulsion on the foetus (within its amnion) 10-30 minutes

3. expulsion of the foetal membranes via additional abdominal contractions up to 3-4 hours post foaling

what would be the normal time placenta should have been passed?

1 hour

what prevents foals getting too big in the mares?

when foetus is at full size which is limited to the size of the placenta of the mare it secretes hormones ready for birth

what is the gravid horn?

where the foal developed in the uterus

what is the non gravid horn?

the horn the foal didn’t develop in

what is the cervical star?

where the placenta attaches to the cervix

what must you check once placenta has been excreted?

that it is fully intact by laying out in F shape

when do foals usually stand and suckle after birth?

attempt to stand within 30 minutes and suckle within 2 hours

when should foals get their colostrum intake?

24-36 hours

what happens when the tip of the non-gravid horn is left in the mare?

can cause sepsis and can lead to laminitis

what does A and U stand for?

Ampulla and ureters

what does UB and VG stand for?

urinary bladder and vesicular glands

what does P, CP and BuG stand for?

prostate, crus penis and bulbourethral glands

what does IcM, BsM and RPM stand for?

ischocavernosus muscle, bulbospongiosus muscle and retractor penis muscle

what does UB and DD stand for?

urinary bladder and ductus deferens

what doe PS and GP stand for?

penis shaft and gland penis

what does SC, CM, T and TE stand for?

spermatic cord
cremaster muscle
testes and tail of epididymis

what happens in the testes?

spermatogenesis and testosterone release

what happens in the epididymis?

spermatozoa maturation for 9 days

what does the spermatic cord do?

suspends testicles within the scrotum

what does the ductus deferens do?

transports semen from epididymis

what is the important role of the cremaster muscle?

temperature regulation of the testes as they have to be 4-6c cooler than the body temp

what does the ischiocavernosus muscles and the retractor penis muscles do?

IcM = maintains erection
RPM = retracts penis when not in use

what does the ureter do?

transports urine from kidneys to the bladder