Equine Repro Phys

Anterior pituitary, luteal and follicle stimulation

LH source and principal action

Anterior pituitary, follicle stimulation

FSH source and principal action

Endometrial cups, luteal stimulation

eCG source and principal action

Anterior pituitary, mammary development

Prolactin source and principal action

Hypothalamus, LH/FSH release

GnRH source and principal action

Follicles, FSH inhibition

Inhibin source and principal action

Pineal gland, seasonality

Melatonin source and principal action

Uterus/placenta, prep for foaling

Relaxin source and principal action

Hypothalamus/posterior pituitary, smooth muscle contraction

Oxytocin source and principal action

Follicles/CL/conceptus, estrous behavior, prep of the uterus

Estrogen source and principal action

CL/conceptus, support pregnancy

Progestin source and principal action

Follicles/adrenals, FSH regulation

Androgen source and principal action

Endometrium, luteolysis, smooth muscle contraction, migration

Prostaglandin source and principal action

13-15

How many endometrial folds run along the uterus and cervix of the mare?

Stratum compactum, stratum spongiosum

Parts of endometrium in the mare

Longitudinal, circular

Types of muscle in myometrium of the mare

Myometrium

Essential role in uterine contractility and clearance

• Embryo migration

• Post-breeding induced inflammation

Kenney and Doig classification

Evaluates number of glands and signs of degenerative changes to estimate the probability of the mare conceiving and maintaining a pregnancy to term

Broad ligament

1. Subdivided into mesovarium, mesosalpinx, and mesometrium

2. Clinical significance: dorsally attached (less prone to uterine torsion), elastosis, copper deficiency, aging, multiple pregnancies

Estrus

Cervix during which phase?:

Relaxed, 2 inches long and ¾ to 1 inch wide

Diestrus

Cervix during which phase?:

Firm (well-toned), 2 inches long

Caslick’s index

Angle of deviation x cm of vulvar length above pelvic brim

Cervix, transverse fold, vulva

Barriers to prevent contamination– “the three seals”

Pneumovagina, pneumouterus

Conditions that lead to uterine infections —> subfertility, placentitis

Clitoris

1. Homologous to the penis

2. Largest among the domestic species

3. Clinical relevance:

   1. Contagious equine metritis (Taylorella equigenitalis)

   2. Source of infection for recurrent contamination of the mare

Glans, corpus, transverse frenular fold, two clitoral sinuses, clitoral fossa

Parts of clitoris

12-24 months

At what age range do horses hit puberty?

Month of birth, nutrition, growth rate, stress (body weight, disease), pheromones, breed

What factors is the onset of puberty in horses dependent on?

Three years old

At what age can a horse start to be bred?

• Not recommended to breed horses anytime before they reach this age due to risk of dystocia!

Puberty

1. First ovulation

2. Somatic development and maturation of the hypothalamic-pituitary ovarian axis

Seasonal long-day breeders, spontaneous ovulators, monoovulatory, monotocous, polyestrous

Classifications of mare repro (seasonality, spontaneous/induced ovulators, mono/polyovulatory, mono/polytocous, mono/polyestrous)

80, 20

1. __% of mares display seasonal activity

2. __% may cycle year-round

Light, breed, age, BCS, humidity, pasture vs. hay, temperature, endorphins, prolactin

Influencing/determining factors of seasonality in horses

Horses, cats

Long-day breeders

Small ruminants, water buffaloes

Short-day breeders

Physiologic/natural breeding season

1. May to August

2. Natural fertile period

3. Less costly controlling seasonality

4. No winter-related problems for early foalings in cold areas

Imposed breeding season

1. Jan. 1st (official birthday)

2. Feb 5-15th breeding season (opening of the breeding sheds)

Better prices at yearling sales, more developed 2-3 year old competitions, less chance of infection (parasites and infectious agents) from the environment

Reasons why breeding season of mares is often altered to be earlier

Anovulatory season (winter solstice)

1. Minimal levels of FSH and LH

2. Ovaries and uterus are small and with low tone (follicles <15 mm)

3. Behavior: unseasonal estrus, paradoxical estrus (unique to horses!)

   1. Lack of inhibition from progesterone

   2. Testosterone from adrenals

4. Cervix is flaccid, pale, dry

Spring transition (spring equinox)

1. Erratic estrous cycles

   1. Melatonin drops rapidly in Feb.

   2. LH stores increase slowly until there is enough to have a surge that triggers ovulation

2. Anovulatory follicles

3. Mismatched ovaries/uterus

Fall transition (fall equinox)

1. Erratic estrous cycles

   1. Melatonin increases

   2. GnRH output decreases

   3. Lack of LH surge

2. Anaovulatory follicles

21-24 days with 5-7 days of estrus

What is the estrous cycle length in mares? How many days of estrus do mares undergo?

Hypothalamus-pituitary-gonadal axis

1. LH and FSH secretion have a divergent pattern

   1. Periovulatory period

      1. LH on the rise– it is not a peak but a surge!

      2. FSH is low

   2. Midluteal phase

      1. LH is low

      2. FSH peaks

LH increases, FSH is low

What happens to LH and FSH during the periovulatory period?

LH is low, FSH peaks

What happens to LH and FSH during the midluteal phase?

Primary follicles

Start in mid-diestrus and result in ovulation during estrus

Secondary follicles

Start in late estrus or early diestrus and result in diestral ovulation or atresia

QH, ponies

Which types of mares have minor follicular waves (no deviation) instead of major secondary follicular waves?

Secondary follicular waves

Which type of follicular wave may result in a prolonged luteal phase? —> May result in twins if the mare is bred

Estrus

1. 5-7 days (range: 2-12 days) characterized by presence of one dominant follicle (in more rare cases, there are 2-3)

2. Receptive sexual behavior (clitoris eversion (“winking”), urinating, tail to the side, resistance to move)

Progesterone, estrogens

1. Receptive sexual behavior is determined by the absence of ___ but enhanced by the presence of ___.

   1. Mares in anestrus can accept mating.

   2. Teaser mares are ovariectomized.

22, 19

At the time of deviation, the largest and second-largest follicle has an average size of __ and __ mm

Follicular synthesis; release of estrogens, inhibin, and IGF system

Dominant follicle suppresses circulating concentrations of FSH, most probably due to what reasons?

Estrus

Which stage of estrous cycle?:

1. Tail raising

2. Squatting, tipping pelvis

3. Urinating

4. Everting clitoris

Diestrus

Which stage of estrous cycle?:

1. Switching tail

2. Kicking, squealing

3. May bite and strike at stallion

4. Moving away from stallion

Ideal teaser stallion

1. Vocal

2. Good libido

3. Gentle

4. Easy to handle

Ovulation

1. Pre-ovulatory follicle variable with body size (35 to 70 mm)

   1. Drafts > Light breeds

   2. Thoroughbred and warmblood > Pony

   3. Most mares and breeds 40-50 mm

   4. Season effect (larger early in the breeding season)

   5. Occur in the ovulatory fossa ONLY

      1. Physical limitation to multiple ovulations

Multiple ovulations

1. Thoroughbreds (>50-19%); QH; Appalosas, Standardbreds (6-10%)

2. Effects of age (older > younger), season (increases late in season), ovulating inducing agents (GnRH agonists, hCG contradictory reports), Barren and Maiden > lactating

3. Synchronous (~24 hours apart) vs. asynchronous multiple ovulations

4. Triple and quadruple ovulations are extremely rare

Diestrus

1. Requires 5 days for CL to mature

2. Less variable (14-15 days)

3. Progesterone dominance

Granulosa, theca

Only the ___ cells transform into luteal (small and large) cells). ___ cells degenerate.

Large

In horses, only the ___ [small, large] luteal cells produce progesterone and have LH receptors.

True

True or false?:

Mares do not express oxytocin in the CL.

Oxytocin, pituitary

As in other species, the release of equine endometrial PGF2alpha is stimulated by ___. During late diestrus, initial oxytocin secretion is most probably originating from the ___.

Hypophysis

Another word for pituitary gland

Endometrium

In contrast to other species, no significant luteal oxytocin synthesis exists in the mare, but the horse is the only domestic species where oxytocin has been localized in the ___.

PGF2alpha

(Both blanks are the same hormone.)

1. In the mare, the initial signal for luteolysis is endometrial secretion of ___ during the late luteal phase.

2. Equine corpus lutea have much higher binding affinities for ___, resulting in greater sensitivity to this hormone.

False

True or false?:

There is counter-current transfer (i.e. between uterine vv. and ovarian aa.) of PGF2alpha in mares

Uterotubal junction, UFOs (unfertilized oocytes)

1. Selective transport of embryo through the ___ because of secretion of PGE2 (also used clinically!)

   1. ___ do not pass

   2. If you have ___ [same word as previous blank] in the embryo recovery filter, look further for embryo

Embryonary capsule

1. Composition: mucin-like glycoproteins; galactose, N-acetylglucosamine, sulfated sugars, and sialic acid

2. Functions:

   1. Anti-adhesive (sialic acid residue)

   2. Maintain spherical shape

   3. Signaling to endometrium for MRP

True

True or false?:

Zona pellucida sheds 24 hours from entrance in the uterus

• No hatching like in ruminants

Embryo migration

(Day 6 to fixation at day 16.5-17)

1. Day 9 to 11: 60% of the time in the uterine body

2. The embryo moves from one horn to the other one 10 to 20 times per day

PGE1, PGE2, PGF2alpha

The migration is supported by uterine contractions caused by ___, ___, and ___ produced by the embryo.

Fixation

Happens at the base of one of the two uterine horns

• Site of future ___ can be predicted 1-4 days before it occurs, as endometrial thickness at the mesometrial aspect at the future site increases significantly.

Increase in size of conceptus, increase in uterine tone, less sialic acid residue in capsule

Mechanisms of fixation

Body pregnancy, early pregnancy loss

1. Fixation in the uterine body

   1. Cranial body = ___

   2. Caudal body = ___

Deprivation hypothesis

Natural twin reduction in mares

Day 16 of embryo

1. <50% of the yolk sac wall has mesoderm

2. Folds of ecto- and mesoderm gives rise to the amnion

3. Hyperechoic lines are specular reflection artifacts, not the ICM

Heartbeat check

1. Amniotic cavity is completed

2. Allantois started to emerge from hindgut

3. Heartbeat present at 21-22 days of gestation

30-day pregnancy check

1. Allantoic and yolk sac cavity are 50:50

2. Chorionic girdle cells start differentiating

21-22 days

When does the equine embryo start to have a heartbeat?

Endometrial cups

1. Formed from the chorionic girdle (CG) (invasive trophoblastic cells) 35-38 days

2. Secrete equine chorionic gonadotropin (eCG)

3. eCG (FSH-like activity in pigs/ruminants) in mares has a LH-like activity

4. Luteinizes and/or induces ovulation of growing follicles = accessory and secondary CLs

5. eCG starts 35-40 days, peaks at 60-80 days, and sloughs off by 120-150 days

Endometrial cups

What secretes eCG?

Primary CL, secondary CLs, placenta

1. Sources of progesterone:

   1. ___

      1. Ovulation to 100-120 days

   2. ___

      1. 35 to 100-120 days

   3. ___ takes over around 100 days until foaling

150

Progesterone is in very low concentration from ___ days to parturition (~340 days)

5-alpha-dihydroprogesterone

Other progestogens maintain pregnancy from 150 days to term, particularly ___.

Primary corpora lutea

Result from single or multiple ovulations during the follicular phase (estrogen dominance)

Secondary corpora lutea

Result from ovulations during the luteal phase (diestrus ovulation; > 2 days from the primary ovulation) or early pregnancy (progesterone dominance, under influence of eCG)

Accessory corpora lutea

Result from luteinization of anovulatory follicles during early pregnancy under influence of eCG

Supplemental corpora lutea

Includes secondary and accessory corpora lutea that develop during early pregnancy

Corpus hemorrhagica

Primary or secondary corpora lutea that develop an intraluteal fluid-filled cavity subsequent to ovulation

Corpora albicantia

Regressed corpora lutea

110-120

1. Uteroplacental shift

   1. At ___ days

40

1. Placentation

   1. ~__ days of gestation

   2. Epitheliochorial

   3. Micro-cotyledonary

   4. Diffuse

5-7

1. Last months of pregnancy

   1. ___ months of gestation: the fetus cannot rotate on its longitudinal axis

      1. Gravid and nongravid horn

330, 380

1. Duration of pregnancy

   1. Variable length: between ___ and ___ days of gestation

Night

What time of day do horses usually foal?

Large, small

1. Foaling monitoring

   1. ___ farms: continuous monitoring, video cameras

   2. ___ farms: no monitoring or are shipped to nearby facilities for foaling

Stage 1

Which stage of parturition?:

1. Rolling, pawing, kicking, and looking at abdomen

2. Walking

3. Sweating

4. Flehmen response

5. Seclusion

6. Frequent passage of manure and urine

7. 0.5 to 6 hours (or longer)

Stage 2

Which stage of parturition?:

1. Rupture of chorioallantois

2. Recumbency

3. Active abdominal and uterine contractions

4. Delivery of foal

5. <30 minutes

Stage 3

Which stage of parturition?:

1. Expulsion of the placenta

2. 3 hours

3. True emergency = risk for metritis, laminitis, endotoxemia, death