Pregnancy failure Flashcards
What is the difference between conception failure and embryonic death?
Conception failure – Fertilisation doesn’t occur, or embryo fails to implant
Embryonic death – Fertilisation occurs, but embryo dies before maternal recognition of pregnancy
In what species is early pregnancy loss common?
Cattle
Pigs
Horses
What are the main causes of conception failure in cattle?
Metabolic or physical stress
Ovarian pathologies (e.g. cystic ovaries)
Poor oestrus detection
Mis-timing of AI (insemination too early or too late)
What is the difference between embryonic death, fetal death, stillbirth, mummification, and maceration?
Embryonic death – Loss of pregnancy before fetal stage
Fetal death – Death after fetal stage has begun
Stillbirth – A dead fetus expelled at term
Mummification – Desiccation of dead fetus within uterus
Maceration – Decomposition of dead fetus within uterus due to bacterial infection
How does the timing of pregnancy loss affect the clinical outcome?
Early embryonic loss → Resorption, often unnoticed
Mid to late gestation loss (after fetal mineralisation) → Mummification or expulsion
Post-luteoplacental shift → Expulsion
In what cases would fetal death after mineralisation but before L-P shift result in expulsion rather than mummification?
In cases of bacteria/inflammation, uterus would produce PG which would lyse CL & result in expulsion
What is the luteoplacental shift and how does it influence fetal death in different species?
Luteoplacental shift is when placenta takes over progesterone production from corpus luteum
In species with early shift (e.g. mare, ewe) → Fetal death likely leads to expulsion
In species with no shift (e.g. sow, bitch, queen) → More likely to result in mummification
What would be the effect of exogenous prostaglandins in species with no placental shift?
Abortion at any stage of pregnancy
Could be used to induce parturition
What would be the effect of exogenous prostaglandins in species with early placental shift?
Resorption of early pregnancy only
Could not be used to induce parturition
How does placentitis affect pregnancy in mares?
Bacterial contamination can ascend through open cervix
Leads to inflammation, fetal growth restriction, or fetal septicemia
Treatment: Local antibiotics in cervix may help prolong pregnancy but are risky, also use systemic antibiotics
How does negative energy balance (NEB) contribute to early embryo loss?
- NEB reduces GnRH & LH secretion → Poor follicle development
2a. Poor follicles → Low oestrogen → Weak oestrus expression
2b. Poor follicle development → Poor oocyte quality → Increased embryo loss
2c. Poor follicles → Weak corpus luteum (CL) → Low progesterone → Compromised uterine environment
How does heat stress contribute to embryo loss?
Direct effects on reproductive endocrine system
Reduces feed intake, worsening negative energy balance
Impaired follicle development → Poor oocyte quality
Uterine stress → Poor embryo survival
How does a poor-quality follicle contribute to pregnancy failure?
Follicles nurture oocyte; if they develop poorly, oocyte is compromised
Poor oocytes reduce fertilisation success or lead to early embryonic death
How does a weak corpus luteum (CL) contribute to embryo loss?
Weak CL → Low progesterone → Poor uterine support
Compromised uterine environment increases risk of embryonic mortality
How does poor embryonic development lead to early embryo mortality in cows?
Failure to secrete maternal recognition signal
This occurs due to:
- Lack of progesterone → Inadequate luteal support
- Attenuated uterine secretions of histotroph (nutrient-rich fluid essential for embryo survival)
Without maternal recognition, luteolysis occurs & pregnancy is not maintained
What can be done to prevent poor embryonic development leading to early embryo mortality in cows?
No product licensed but could stimulate progesterone production with GnRH or
Supplement with progesterone
Timing & identification of problem animals is critical
What factors contribute to embryonic loss in sheep?
Multiple conceptions
Infectious causes:
- Toxoplasmosis, Schmallenberg virus, Border disease → Embryonic loss & return to oestrus
Nutritional factors:
- Flushing with fresh grass – Increases ovulation but needs balance
- Red clover grazing (high phytoestrogens)
Management factors:
- Early breeding season
- Ram-to-ewe ratio
What are the major causes of conception failure in pigs?
Seasonal infertility
- Decreased fertility in summer/autumn
Ovulation failure & ovarian cysts
- Post-weaning, undernutrition, stress
- Poor response to treatment → Culling is likely
Genetics
- Ovulation rates doubled, but embryonic survival declined due to limited uterine capacity
Infectious causes:
- Porcine parvovirus (PPV) → Embryonic death & resorption
- Fetal period PPV infection → Mummification
Nutritional impact:
- Feed restriction increases subfertility
How does age influence early pregnancy failure in mares?
Young mares: Immature reproductive system, inadequate nutrition, or physical stress
Older mares: Acquired structural defects, uterine issues
What are the main causes of early pregnancy failure in mares?
Age
Haemorrhagic anovulatory follicles (HAFs)
Uterine pathology due to inflammatory conditions or lack of histotroph
- e.g. endometritis due to delayed uterine clearance of bacteria post-foaling
- Infectious diseases (e.g. contagious equine metritis)
Foal heat
Maternal stress due to pain, undernutrition or transport
What are Haemorrhagic anovulatory follicles (HAFs) in mares?
Mares don’t get cysts but can have failure of ovulation –> haemorrhagic anovulatory follicles
How does the presence of multiple conceptuses affect pregnancy outcomes in mares?
Common cause of pregnancy loss in mares
Results from multiple ovulations → competition for placental space
Early detection allows for manual reduction (pinching) of one embryo before fixation
What can you see in this ultrasound of a mare with a broad soft cervix?
Follicle in each ovary
R follicle is more mature & close to ovulation
What can you see in this ultrasound of a mare 14 days after breeding?
CL in both ovaries & conceptus in L uterine horn
Define zygote
Product of conception
Define embryo
Mass of tissue, within zygote, that will form living body that has not yet reached stage of differentiation
At what stage is an embryo considered a fetus?
From the completion of differentiation (similar time as mineralisation) onwards
Define resorption & abortion
Resorption – loss of embryo (before mineralisation)
Abortion – loss & expulsion of fetus (after mineralisation)
Describe progesterone levels throughout pregnancy.
- Ovulation occurs
- P4 goes up & plateaus
- P4 falls just before parturition
P4 levels vary between species
- In some P4 is produced entirely by CL (ovarian production of P4) throughout pregnancy
- In other species placenta takes over (luteal-placental shift)
What are the possible outcomes of fetal death?
Abortion – Expulsion after P4 decline & uterine contractions
Mummification – Dehydration of fetus, P4 maintained, no bacteria
Maceration – Bacterial invasion, putrefaction, incomplete expulsion
Stillbirth – Fetus reaches full term but dies during delivery
What are some common non-infectious causes of pregnancy loss?
Genetic abnormalities
Uterine disease (not able to form effective placenta)
Stress (nutritional, heat, other)
Maternal illness
Nutritional phytotoxins
What are the infectious causes of pregnancy loss?
Exposure to reproductive pathogens
- Not always venereal – Many infections occur after pregnancy begins
Recrudescence of latent viral infections
Ascending infections (e.g. placentitis)
Few bacterial venereal pathogens cause pregnancy loss:
- CEM in mares → endometritis only
- Campylobacteriosis in cattle → Endometritis but may cause abortion if persistent
