reproductive function in horses

Question 1

Mare reproductive characteristics

Answer 1

puberty 12-24 months

seasonally polyestrus

Question 2

stallion repro characteristics

Answer 2

puberty 4-5 years

functional year round- sperm numbers, ejaculate volume

Question 3

season cycle

Answer 3

with winter solstice no cycling because less daylight

Question 4

affect of daylight

Answer 4

perceived through optic N/ chasm

with sunlight pineal gland= decreased melatonin which acts on hypothalamus to increase GnRH acting on Ant. pituitary to increase FSH and LH which act on ovary to increase E2 and P4

throughout spring GnRH and LH accumulate

LH= maturation of follicle, induces estrogen production

Question 5

collection of transitional equine follicles

Answer 5

have 3-4 waves of follicle production prior to mature release at estrus

Question 6

ovarian characteristics in vernal transition

Answer 6

transitional ovary= not long enough to ovulate but have follicles present

behavior= prolonged heat- because follicles present but not ovulated then needs to stand to be bred when in heat

Question 7

uterine characteristics in vernal transition

Answer 7

cervix, body and two hors

Question 8

first ovulation in mare

Answer 8

corpus hemorhagicum- palpable and present for 24 hours

amount of LH needed for ovulation

Question 9

universal birthdate

Answer 9

January 1st- in effort to unify and have horse not be young because of the universal bday want to breed when not ideal breeding season

breeding via AI
physiologic breeding season- april to september
operational breeding season- february to july

Question 10

managing transition in breeding season

Answer 10

artificial lighting programs

stimulates daylight
accelerates time to first ovulation
does NOT shorten transition (estrous not shorter just shifted)- begin dec. 1 first ovulation feb. 15

Question 11

summer

Answer 11

ovulatory receptive because of day length

long day= less melatonin

Question 12

estrous cycle in mare

Answer 12

18-21 days

follicular phase- estrus (4-7 days)
luteal phase- diestrus (14 days)

Question 13

follicular phase

Answer 13

largely function of daylight

estrus
large preovulatory follicle grows stimulating ovulation, which is ovulated decreasing estrogen

biphasic release of FSH- low degree prior to ovulation and 2nd in middle of cycle

estrogen and LH rise concurrently with preovulatory follicle during estrus phase

peak LH= post ovulation- not normal but has to do with fact that have follicles but not ovulating

Question 14

luteal phase

Answer 14

dominated by CL
should remain constant

Diestrus

begins with ovulation (24-48 hrs) before end of estrus

corpus hemorrhagicum
CL- progesterone (pregnancy maintenance, if not pregnant PGF2a causes CL lysis so can re-enter heat)

Question 15

estrus- follicular phase, follicles

Answer 15

dominant follicles- recruited early (8-10 mm) 
pre-ovulatory size large (40-50mm) 
produces estrogen (CS)

Question 16

winking

Answer 16

+ sign of estrus

Question 17

behavior in estrus

Answer 17

receptive

discharge and urination, winking

Question 18

transracial ultrasound during estrus

Answer 18

edema within the uterine wall

urine- contains pheromones

Question 19

cervical evaluation during estrus

Answer 19

no estrogen= pale pink, tight

as estrogen increases, will relax

Question 20

ovulation in mare

Answer 20

equine, cortex inside and medulla surrounds

always ovulates through ovulation fossa, cannot palpate CL because of fossa

Question 21

preovulatory follicle

Answer 21

means ready to breed the mare

Question 22

maternal recognition of pregnancy

Answer 22

if not signaled endometrium releases so will cycle again because prostaglandin increases and progesterone decreases

Question 23

diestrus behavior

Answer 23

not receptive, mare= violent

pale cervix, not relaxed

Question 24

end product of estrus

Answer 24

14 days post breeding check to see if pregnant

if pregnant embryo signals to lumen for maternal recognition

Question 25

fall transition

Answer 25

shorter days= increased melatonin
decreased GnRH
decreased LH and FSH
decreased estrogen and P4

unpredictable behavior

Question 26

winter an estrous

Answer 26

equine industry- ambient temp imps. warmer can cycle longer

during transitional periods LH administration doesn’t always work

closer to equator see more round the year cycling

same hormonal effects as fall

ovary with no large preovulatory follicles present

Question 27

conclusions

Answer 27

mare= seasonal breeders- long days initiate cyclicity

hormones drive the cycle- hypothalamic pituitary gonadal axis

Question 28

seasonality affects both mares and stallions

Answer 28

reproductive function maximal during long days

mare- consistent cyclicity
stallion- increase sperm numbers and ejaculate volume