Reproductive Anatomy & Physiology of the Mare

Question 1

The cervix in the mare is approximately how long?

Answer 1

10-15 cm

Question 2

What is the most sensitive organ to hormonal stimulation in the mare?

Answer 2

Cervix

Question 3

The cervix in the mare is closed and dry under the influence of what hormone?

Answer 3

Progesterone

Question 4

The cervix in the mare is low, relaxed and moist under the influence of what hormone?

Answer 4

Estrogen

Question 5

Are ovaries located more laterally in the cow or mare?

Answer 5

Mare

Question 6

What shape is the uterus of the mare?

Answer 6

Y or T shaped

Question 7

What attaches the reproductive tract to the abdominal wall and may make the ovaries difficult to locate?

Answer 7

2 broad ligaments

Question 8

The extensive mesovarium in a mare can mean what?

Answer 8

Wide variation in ovarian position

Question 9

The uterus has about how many folds that run from the tip of the horns to the cervix?
What do these aid in?

Answer 9

• 12-14 folds

- Fluid evacuation

Question 10

What are 3 functions of the oviduct?

Answer 10

• Sperm storage
• Fertilization site
• Embryo transport

Question 11

Unfertilized ova are retained where?

Answer 11

Oviduct

Question 12

Fertilized ova (embryos) descend to where?
When?

Answer 12

• Uterus

- 5.5 days after fertilization

Question 13

The UTJ opens in response to what?

Answer 13

PGE

Question 14

The ovaries in the mare tend to be around what vertebrae?

Answer 14

3rd or 4th lumbar vertebrae

Question 15

Where is the site of ovulation on the ovary of a mare?

Answer 15

Ovulation fossa

Question 16

Mature follicles are what size?

Answer 16

40+ mm

Question 17

The further away from the ovulation fossa the oocyte is, the more dramatic the what?

Answer 17

Follicular change in shape (follicle oblongation)

Question 18

The mare’s udder has how many halves?

Each half has how many glands?

Answer 18

• 2 halves

- 2 glands

Question 19

How many orifices are in each teat in the mare?

Answer 19

2

Question 20

Regulation of the reproductive cycle of the mare is governed by what?

Answer 20

Hypothalamic-pituitary-gonadal axis

Question 21

The majority of mares show signs of heat during what months?

Answer 21

May to August

Question 22

Mares that have little to no ovarian activity and the uterus is flaccid with no tone are in what part of the cycle?

Answer 22

Anestrous

Question 23

Short days stimulate what in the mare?

Answer 23

Stimulate the pineal gland to release melatonin that inhibits GnRH production.

Question 24

How long is artificial lighting set for?

Answer 24

16 hours of light and 8 hours of dark

Question 25

What size light bulb should be used for artificial lighting in a 12 x 12 stall?

Answer 25

200 watt

Question 26

What is artificial lighting used for?

Answer 26

Advances transitional phase

Question 27

What hormone can be used during seasonal anestrous to bring the mare out of anestrous? What dose?

Answer 27

- GnRH | - 20-25 ug TID IM for 2-3 weeks

Question 28

T/F: During the transitional phase, mares have multiple, variable size follicles.

Answer 28

True

Question 29

How does the uterus appear during the transitional phase in a mare?

Answer 29

Uterus has estrual tone with evidence of uterine edema.

Question 30

When does the transitional phase in a mare end?

Answer 30

With the first ovulation of the year.

Question 31

What dose of progesterone can be given to reduce the length of the transitional period in a mare?

Answer 31

150 mg IM SID for 10 days

Question 32

What dose of progestogens (Altrenogest) can be given to reduce the length of the transitional period in a mare?

Answer 32

0.044 mg/kg PO SID for 10 days

Question 33

What are 2 examples of dopamine antagonists that can be used to reduce the length of the transitional period in mares?

Answer 33

- Domperidone (PO) | - Sulpiride (IM)

Question 34

Behavioral estrus is a result of estrogen acting on what receptors?

Answer 34

Alpha receptors of the brain

Question 35

T/F: The sensitivity of estrogen is the same between mares.

Answer 35

False - The sensitivity of estrogen is VARIABLE between mares.

Question 36

Is behavioral estrus a reliable breeding management tool to use in mares?

Answer 36

No

Question 37

During physiologic estrus, the mare is under the influence of what hormone?

Answer 37

Estrogen

Question 38

There is up regulation and activation of what type of receptors during physiologic estrus?

Answer 38

Follicular LH receptors

Question 39

Circulating estrogen levels are important for up regulation of what receptors?

Answer 39

Oxytocin receptors

Question 40

Physiologic estrus starts around what day if ovulation is day 0?

Answer 40

Day 17

Question 41

What is the normal inter-ovulatory interval in a mare?

Answer 41

19-22 days

Question 42

What are 3 methods of estrus detection in the mare?

Answer 42

- Teasing - Rectal palpation/vaginoscopy - US

Question 43

What are 4 observations made with rectal palpation/vaginoscopy during estrus?

Answer 43

- Hyperemic moist elongated vulva - Soft cervix - Turgid uterus - Presence of a follicle

Question 44

What are 2 observations made using US during estrus?

Answer 44

- Hyperplasia/edema of uterine folds | - Large dominant follicle

Question 45

At any stage during diestrus in the mare, an ovary may contain what?

Answer 45

Antral follicles of less than 2 to greater than 35 mm in diameter at different stages of growth and regression.

Question 46

The major primary wave starts with what? | Finishes with what?

Answer 46

- Starts with uterine PGF | - Finishes with ovulation

Question 47

To distinguish between growing and regressing follicles of the ovulatory wave, what is necessary?

Answer 47

More than one US exam.

Question 48

What is a key component for proper breeding management?

Answer 48

Manipulation of the estrous cycle

Question 49

How large must a follicle be in order to be able to induce ovulation?

Answer 49

Greater than 35 mm

Question 50

What must be present in the uterus to induce ovulation? | What are 2 components of this?

Answer 50

- Uterine edema | - Estrogen exposure and LH receptors

Question 51

When does ovulation usually occur once induced?

Answer 51

24-48 hours

Question 52

What are 4 examples of ovulation induction hormones?

Answer 52

- Human chorionic gonadotropin (hCG) - Deslorelin injectable (Sucromate) - Deslorelin pellet (Ovuplant) - Recombinant LH (rLH)

Question 53

When does ovulation occur when induced by Ovuplant?

Answer 53

38-42 hours

Question 54

What is a drug that is very effective to induce ovulation in mares with good edema and a dominant follicle (35-42 mm)?

Answer 54

Ovuplant (Deslorelin)

Question 55

What is a good choice for ovulation induction with fixed time insemination programs with cooled and/or frozen semen?

Answer 55

Ovuplant (Deslorelin)

Question 56

What are 2 advantages of using Deslorelin vs hCG to induce ovulation in a mare?

Answer 56

- Highly effective | - Wider window for treatment

Question 57

What are 3 possible causes of failure to respond to ovulatory inducing agents?

Answer 57

- "Immature follicles" (not enough LH receptors) - Mare not in estrus even though large follicle is present - Anovulatory follicles (AHF)

Question 58

What are 4 criteria to determine whether or not a CL is present on US?

Answer 58

- Diameter - Volume/area of the CL - Luteal tissue echogenicity - Doppler showing vascularization of CL

Question 59

T/F: The US appearance of the CL is a good indicator of its functionality and its age.

Answer 59

False - It is NOT a good indicator of functionality or age.

Question 60

What are 5 possible indications that an anovulatory follicle (AHF/HAF) is present?

Answer 60

- Fails to ovulate in response to ovulatory inducing agents - Increases in size beyond normal - numerous free-floating echoic specks in the antrum - Single fibrin tags floating in FF - Organized fibrin in antrum

Question 61

What are 2 estrus induction agents that are luteolytic?

Answer 61

- Prostaglandin F2 alpha (Lutalyse) | - Cloprostenol (Estrumate)

Question 62

When progesterone levels from to what level in what amount of time, this induces estrus?

Answer 62

Less than 1 ng/mL in about 24 hours

Question 63

A CL must be how many days old in order to be fully responsive to prostaglandin?

Answer 63

5 days old

Question 64

It is suggested to examine mares when in order to better predict the PGF response?

Answer 64

At the time of treatment.

Question 65

What are 2 things prostaglandins should not be used for?

Answer 65

- Ovulation induction | - Uterine evacuation post-ovulation

Question 66

What are 4 other uses for progesterone?

Answer 66

- Prolong luteal phase - Estrus suppression - Estrus synchronization - Pregnancy maintenance