Pregnancy Failure

Question 1

When does pregnancy failure occur?

Answer 1

Early embryonic death (pre-implantation), late embryonic death (peri-implantation), abortion (post-implantation)

Question 2

When is the period of maximal embryonic wastage?

Answer 2

Most wastage occurs very early in gestation, in cows 75% of waste occurs before day 21

Question 3

What are the common causes of reproductive wastage?

Answer 3

Fertilisation failure, embryo mortality (early & late) & abortion

Question 4

How might pregnancy loss result in pseudopregnancy?

Answer 4

Pregnancy loss after MRP, failure of CL regression, progesterone secretion, pseudopregnancy – can occur in the mare, goat, sow and queen

Question 5

What are the two types of pseudopregnancy in the mare following pregnancy loss?

Answer 5

Type I – early embryonic death after MRP, persistent CL and prolonged luteal phase, treat with prostaglandin
Type II – fetal death after endometrial cup formation at day 36, lasts until demise of endometrial cups

Question 6

By what two routes can chromosome abnormalities arise?

Answer 6

Inherited & de novo during gametogenesis, fertilisation and early embryo cleavage

Question 7

What are the main causes of embryonic and fetal loss?

Answer 7

Nutrition, environmental, physiological, infectious agents

Question 8

What developmental stages can be affected?

Answer 8

Early embryo mortality, maternal recognition, gamete transport, fertilisation, late embryo mortality

Question 9

What events prior to fertilisation may result in embryo mortality?

Answer 9

Environmental influences may affect folliculogenesis, folliculogenesis may influence the embryo derived from the oocyte

Question 10

How common are infectious causes of abortion?

Answer 10

In the minority – approximately 15%

Question 11

What are the possible routes of infection?

Answer 11

Cervix, systemic infection, pathogens may affect the CL rather than conceptus

Question 12

What are some of the common infectious agents causing abortion?

Answer 12

Cattle – Campylobacter fetus var. venerealis, Tritrichomonas fetus, Neospora caninum (most common), Bovine viral diarrhoea virus
Horses – Taylorella equigenitalis, Escherichia coli, Aspergillus, Equine herpesvirus-1
Sows – Porcine parvovirus
Ewes – Toxoplasmosis gondii, Border disease virus

Question 13

What determines whether the aborted fetus is in a state of autolysis or fresh?

Answer 13

In species with CL dependent pregnancy there is a delay between time of death and lysis of the CL resulting in autolysis
In species which are CL independent for the most part of gestation fetal placenta leads to cessation of fetal contribution, thus placental progesterone declines and the fetus is expelled in a fresh state

Question 14

What does the outcome of infection depend on?

Answer 14

The age of the fetus at the time of infection

Question 15

What are the signs of porcine parvovirus or PRRS virus?

Answer 15

Stillbirths, mummifications, embryonic death, infertility

Question 16

How does bovine BVD affect calves according to their age?

Answer 16

Early gestation, <100 days – virus +ve
Mid gestation, 90-125 days – virus +ve, antibody –ve
Mid to late gestation, >150 days – virus –ve, antibody +ve (normal development)

Question 17

What are the common infectious causes of ovine abortion?

Answer 17

Schmallenberg virus, Chlamydophila abortus (main cause in the UK), Toxoplasma gondii, Campylobacter species, Salmonella species, Listeria species

Question 18

What are the possible outcomes of Toxoplasma gondii infection?

Answer 18

Resorption, barrenness, mummification, stillbirth, abortion, live lambs

Question 19

Why do Chlamydia and Campylobacter spread rapidly?

Answer 19

Organisms present in large numbers in aborted products

Question 20

How does the incubation period for enzootic abortion differ in goats compared to sheep?

Answer 20

Shorter – infection and abortion can occur in the same year

Question 21

What are the common causes of non-infectious pregnancy loss in the common species?

Answer 21

Cow – nutrition, stress, timing of insemination, conception too soon after calving
Sow – failure to establish pregnancy (pre-attachment before days 13-14), nutrition, stress, litter size, age of sow, weight of sow
Ewes – considered to be low – diet, multiple conceptus
Goats – high in Angora goats as increased metabolic demand for fibre production

Question 22

What is the link between pregnancy loss and ovulation rate in the sow?

Answer 22

Negative correlation – as ovulation rate increases, embryo survival decreases

Question 23

Is abortion a problem in the bitch and queen?

Answer 23

Limited evidence to suggest abortion is a clinical problem in bitch and queen

Question 24

What are the various types of equine pregnancy failure?

Answer 24

Early embryonic death – before MRP
Embryonic death – before 40 days
Early fetal death – 60-100 days
Late fetal death – after 150 days
Abortion – before 300 days
Stillbirth – after 300 days

Question 25

What are the clinical signs of a failing pregnancy?

Answer 25

Early embryonic death – tissues resorbed and the animal returns to oestrus
Death following infection – pyometra
Expulsion of abortus tissue – death of some, but not all, fetuses during the first half of pregnancy may result in lysis of the CL and immediate expulsion
Fetal mummification – develops in multiparous bitch, queen and sow, mummified fetus expelled at parturition with no harm to live fetuses

Question 26

Why does equine twinning result in pregnancy failure?

Answer 26

Placenta is epitheliochorial, conceptus is reliant on nutrition rom the entire surface area of the endometrium, twins run out of room and compete for nutrients

Question 27

What are the manifestations of pregnancy loss in twin pregnancies?

Answer 27

One fetus is resorbed at an early stage OR one fetus is mummified at an early stage OR both twins are aborted, usually mid to late gestation

Question 28

What is aneuploidy?

Answer 28

One or two chromosomes too few or too many

Question 29

What is polyploidy?

Answer 29

Whole multiples of the haploid number

Question 30

What structural chromosomal abnormalities can occur?

Answer 30

Deletions – genetic material lost

Insertions, inversions & translocations – genetic material re-arranged