Pregnancy impending parturition

Question 1

Tubal transport

Answer 1

Around day 4-5 after fertilisation, the embryo secretes PGE2 causing the muscular sphincter of the oviduct to relax, allowing the embryo to pass out into the uterus

Question 2

Conceptus migration

Answer 2

The blastocyst remains mobile until around day 16 and moves throughout the lumen of both horns and body of the uterus
At day 16, the conceptus becomes fixed at the base of the uterine horns

Question 3

Blastocyst capsule

Answer 3

Formation of an acellular glycoprotein ‘capsule’ that completely envelopes the conceptus during its initial intrauterine period
Forms at around day 6.5 after ovulation and increases in size to accommodate conceptus growth until day 18, progressively thins until it is lost by day 23

Question 4

Protective functions of the blastocyst capsule

Answer 4

Provides physical protection for the delicate conceptus during the mobile phase
Anti-adhesive properties that ease conceptus mobility, and protects the embryo against microbial infection
Acts as a filter, allowing exchange of signalling molecules and nutrients between the embryo and the dam

Question 5

Embryo vs foetus

Answer 5

Embryo = the period up to 60 days after fertilisation
Foetus = after 60 days

Question 6

What is the hormone responsible for maternal recognition of pregnancy in horses

Answer 6

Progesterone

Question 7

When do blood progesterone levels in mares rise above baseline levels?

Answer 7

Within 24-48hrs of ovulation

Question 8

What happens if the mare does not conceive or is not mated during days 12-16 after ovulation

Answer 8

The endometrial lining of the uterus releases PGF2a causing the destruction of the CL and a rapid fall in blood progesterone levels

Question 9

What is the importance of maintaining the CL in pregnant mares

Answer 9

High progesterone levels prevent the mare from returning to oestrus and ensure that the cervix remains tightly closed, preventing ascending infections. Progesterone also stimulates the endometrial glands to secrete “uterine milk” that is essential for the nutrition of the equine conceptus before it forms a true placenta.

Question 10

What biochemical message does the developing conceptus send to its dam between days 10 and 16 after ovulation

Answer 10

The developing conceptus sends a biochemical message (believed to be estrogen) to its dam to prevent the release of PGF2α from the uterus, ensuring the maintenance of the corpus luteum.

Question 11

What are the two aspects of conceptus development that are unique to equids and affect the way in which the conceptus sends its vital message to its dam

Answer 11

The remarkably prolonged period of intrauterine conceptus migration/mobility and the presence and persistence of the blastocyst “capsule”

Question 12

When does true implantation occur

Answer 12

Very late in horses, day 40-42, as a result of the slow development of the fetal membranes

Question 13

What is the name of the glycoprotein that envelops the embryo from day 6.5-23

Answer 13

Blastocyst capsule

Question 14

What happens between days 18 and 35 of the pregnancy

Answer 14

Marked increase in uterine tone that fixes the embryo at the base of one uterine horn

Question 15

What is the name of the structure that secretes equine chorionic gonadotrophin (eCG) from days 40-120 of gestation

Answer 15

Endometrial cups

Question 16

What is the function of oestrogens during pregnancy

Answer 16

Oestrogens required for growth and development of the foetus

Question 17

What is the significance of the tendency for implantation to occur in the uterine horn contralateral to the previous pregnancy

Answer 17

Helps to ensure adequate blood supply to placenta and prevents competition between developing foetuses

Question 18

What is teasing behaviour in relation to stud management

Answer 18

Teasing behaviour is a method of routine stud management in which mares are teased daily or every other day from 14-23 post cover/insemination to determine their pregnancy status. Aggressive rejection of the stallion usually occurs in pregnant mares, but teasing can be difficult in mares in prolonged dioestrus, difficult mares in oestrus, and lactational anoestrus after foal heat.

Question 19

What is vaginoscopy and how is it used for pregnancy diagnosis in mares

Answer 19

Vaginoscopy is a method of pregnancy diagnosis in which a speculum is used to examine the cervix. In pregnancy, the cervix should be pale, dry, often with obvious blood vessels, tightly closed, and pedunculated with the canal plugged with mucus. However, some mares can have a relaxed cervix and mares under progesterone influence can give false positives (i.e. prolonged dioestrus).

Question 20

What is rectal palpation and how is it used for pregnancy diagnosis in mares

Answer 20

In early pregnancy (days 16-23), the caudal cervix may be palpated as a turgid, fairly rigid body on the floor of the pelvis, along with an enlargement of the base of a uterine horn and increased muscular tone in the whole uterus. However, rectal palpation alone may not be sufficient for accurate pregnancy diagnosis due to difficulties with the enlarged uterus of older mares, and twin recognition is not possible.

Question 21

What are the benefits of ultrasound scanning examination for pregnancy diagnosis in mares

Answer 21

The benefits of ultrasound scanning examination include early pregnancy detection (10-12 days after ovulation), detection of twins and appropriate treatment, a means of checking fetal health and development, determination of fetal sex, and no reported deleterious effects

Question 22

What is the reliability of detection before 14 days post cover/service

Answer 22

In a small, but significant, proportion of mares, an ultrasound examination carried out prior to 14 days post service may not detect a pregnancy which is subsequently recognised on a later scan.

Question 23

What are the two possible reasons for missing a small blastocyst during an ultrasound examination carried out prior to 14 days post service?

Answer 23

a) a small blastocyst was missed (bear in mind the rapid growth from a tiny size which occurs up to this stage), or b) a secondary ovulation may have been fertilised resulting in a pregnancy several days behind in its development in comparison to that expected.

Question 24

When should no action be taken to induce another oestrus in the case of a mare which has not spontaneously returned to oestrus

Answer 24

Before 20 days post service

Question 25

What is the best time for a first scan, especially for twins

Answer 25

14-17 days post cover/insemination

Question 26

What is the reason for carrying out an early scan at a stage when all conceptions will be identifiable

Answer 26

Nearly all twins arise from multiple ovulations, often with a gap of days between. Consequently one pregnancy (usually arising from a late ovulation) often appears to be several days behind in size and development

Question 27

What is the reason for carrying out an early scan before mating

Answer 27

The use of preliminary ultrasound scans before mating may highlight uterine abnormalities (intraluminal fluid, endometrial cysts, intrauterine air etc) and allow easier differentiation from early pregnancies.

Question 28

What are the ultrasound criteria for early embryonic death

Answer 28

conceptus previously present is not seen on 2 consecutive scans or only remnants detected, irregular or indented conceptus, prominent endometrial folds (caused by oedema – ‘cartwheel’ pattern) and/or uterine fluid, conceptual fluid with echogenic spots, no fetal heart rate after 30 days, poor fetal structure definition, conceptus 2 standard deviations smaller than established mean for that stage of gestation.

Question 29

When is the first scan commonly done

Answer 29

16 days after service

Question 30

When is the second scan usually done

Answer 30

28-30 days post service

Question 31

When are subsequent scan dates approximately

Answer 31

Approx 40 ad 60 days after service

Question 32

After what stage of gestation is the mare less likely to lose her pregnancy

Answer 32

After formation of the endometrial cups at 35 days

Question 33

At what stage should twins in a mare be treated by crushing for the best success rates

Answer 33

16 days post service

Question 34

Can unicornate twins be successfully treated by rupture

Answer 34

no

Question 35

What should be considered if one twin has not achieved dominance in a mare with twins

Answer 35

Prostaglandin administration

Question 36

At what stage is termination considered advisable for twins that haven’t been successfully resolved

Answer 36

Prior to endometrial cup formation (around 34 days)

Question 37

What happens if twin pregnancies remain undetected until after 35 days?

Answer 37

Treatment options are limited and attempts to induce a fertile oestrus may be unsuccessful.

Question 38

What percentage of mares with undetected twin pregnancies will give birth to a normal single foal if no action is taken

Answer 38

Approximately 10%

Question 39

What is the success rate of fetal intracardiac injection of potassium chloride for twin reduction

Answer 39

± 40%

Question 40

What long-term effect may twin reduction have on the TB breed?

Answer 40

Promoting the spread of the “twinning gene”

Question 41

At what stage can the gender of an equine fetus be recognised on transrectal ultrasound examination?

Answer 41

Approximately 60 (58-70 days) days of gestation

Question 42

What anatomical difference can be recognised on transrectal ultrasound examination to determine fetal gender in horses

Answer 42

The position of the genital tubercle (GT)

Question 43

What technique allows the determination of fetal sex with greater accuracy in older fetuses (100-160 days) transrectally

Answer 43

Colour doppler ultrasonography combined with B-mode ultrasonography

Question 44

What determines the length of gestation in the horse

Answer 44

The fetus determines the length of gestation in the horse through the hypothalamus-pituitary-adrenal axis, but maternal influence is indicated by the majority of equine births being at night.

Question 45

What is the gestational range of ponies, TBs, and donkeys

Answer 45

The gestational range of ponies is 315 – 340 days, TBs is 320 – 360 days, and donkeys is 360 – 380 days.

Question 46

What are the placental and fetal changes that occur during the period of uterine development leading up to birth

Answer 46

During the period of uterine development leading up to birth, placental and fetal changes occur, including the maturation of the fetal musculoskeletal, cardiovascular, nervous, respiratory, digestive, and endocrine systems.

Question 47

What are the uses of transrectal and transabdominal ultrasounds during pregnancy

Answer 47

Transrectal ultrasound is used to measure the combined thickness of the uteroplacental junction just cranial to the cervical os and assess the echogenicity of the uterine fluids. Transabdominal ultrasound enables assessment of the maturity and viability of the pregnancy, as well as placental membranes, fetal fluids, fetal movement and position, fetal heart rate, and fetal size and growth.

Question 48

What are the fetal movement and position changes during pregnancy

Answer 48

The fetal musculoskeletal system matures, and fetal movement is necessary for proper functional and anatomical development. Fetal activity is greatest between 3 to 4 months gestation, and the presentation, position, and posture of the fetus change before foaling.

Question 49

What are the mare changes during late pregnancy

Answer 49

The mare prepares for delivery and nourishment of her new-born foal, including the transfer of passive immunity. The signs to look for include abdominal size, perineal changes, udder development, mammary gland secretion, behavioural changes, and vulval discharge.

Question 50

When does mammary growth begin and when is the major increment in udder size

Answer 50

Mammary growth begins about a month before parturition, but the major increment in udder size occurs in the last 2 weeks.

Question 51

What is “waxing up”

Answer 51

“Waxing up” is the clotting of a bead of colostrum at the end of the teat, which usually happens 24 hours before birth.

Question 52

What happens to the electrolyte concentrations in mammary secretions during late pregnancy

Answer 52

As the mammary gland develops, the concentrations of Na+, K+, and Ca2+ change. Approximately 2 weeks before delivery, Na+ and K+ concentrations are similar to plasma. In the last 2 weeks of pregnancy, Na+ decreases and K+ increases until K+ rises above Na+, which usually occurs within the last 48 hours of foaling. The Ca2+ levels rise slowly and are greater than 10mmol/l within the last 12-24 hours of parturition.

Question 53

Behavioural changes indicating impending parturition

Answer 53

Restlessness, agitation, sweating, pawing, pacing, hind-quarter cringing, tail clamping, and other signs may occur in mares during the first stage of labour. The mare may move away from the herd and exhibit increased restlessness as birth approaches.

Question 54

First stage of labour

Answer 54

Painful uterine contractions during the first stage of labour are responsible for behavioural changes seen in mares. Signs include patchy sweating, skin temperature increase, pacing, tail clamping, and flehmen response. First stage can last from minutes to hours, and sometimes signs appear but are not followed by second stage labour. Prolonged first stage may indicate problems, such as an abnormally thickened placenta.

Question 55

Hormonal changes

Answer 55

During pregnancy, hormonal changes in both mare and foetus are precisely coordinated, eventually leading to birth. Oestrone sulphate and progestagens are two hormones that can be measured in mid to late pregnancy to assess foeto-placental health. Oestrone sulphate levels rise from approximately 80 days of gestation and peak around day 200-220 before declining. Progestagen levels remain low and constant until around day 300 of gestation in maternal jugular blood before rising in TB mares and declining rapidly 2-3 days prior to parturition. Premature foals often survive due to increased cortisol levels from stress in utero.