Pregnancy failure Flashcards
When does early embryonic death occur?
— Pre-implantation phase
— Before foetal-maternal recognition
— Does not involve elongation of life of CL
When does late embryonic death occur?
— Peri-implantation phase
— Occurs after the life of the CL has been extended
— Luteotrophic factor has been produced
When does abortion occur?
— Post-implantation phase
— After organogenesis
NOTE: Fertility: relates to ability to conceive and
become pregnant, not pregnancy loss.
Approximately 75% of all reproductive pregnancy wastage occurs before . . . in the cow?
Day 21 with the majority occurring between 8 and 18 days after insemination
How do fetal abnormalities arise?
Abnormalities in meiosis:
— Gametes with unbalanced chromosomes
— These can be fertilised to give abnormal embryo
• Polyspermic fertilisation
• Failure to extrude 1 or more polar bodies
. Fertilisation of oocyte and polar body at
first cleavage
. Failure of meiosis
What are some of the causes of embryonic and foetal loss?
Nutritional
— E.g. Vit A and Vit E deficiency: cows, pigs
Environmental
— Climate (high heat)
— Stress
— teratogens (environmental factors that induce fetal
abnormalities during embryogenesis)
Physiological
— Ovulation rate (increased rate in pigs can effect it)
- Uterine environment
. Asynchrony of uterus, ovary and embryo
• Immunological (mothers immune system must tolerate
allogenic fetus expressing paternal antigens)
• Endocrine (lack of progesterone)
• Failure of maternal recognition of pregnancy
. Infectious agents
What are some husbandry and clinical factors that can induce abortion, conception loss?
• Insemination — Semen quality: .May affect fertilisation/embryo quality — Given in error during early pregnancy . May cause embryo loss . Trauma — PD by rectal palpation after 42 days . <2% loss — Palpation of the uterus . Can cause substantial embryo mortality if performed early in pregnancy
What are common infectious agents of abortion?
. Bacterial
• Parasitic
• Fungal
• Viral
What happens to the fetus after early embryonic death?
Tissues resorbed and animal returns to oestrous if no other conceptus in the uterus. As mentioned previously, if prior to maternal recognition of pregnancy then no delay to cycle.
What happens to the fetus after death following infection?
Pyometra may occur
What happens when there is expulsion of the aborted fetus?
— Death of some (but not all) foetuses during the first half of pregnancy may result in lysis of the CL and
immediate expulsion. Foetal death after ossification
As there has been ossification fetus cannot be resorbed.
What happens to cause fetal mummification?
— Papyraceous mummification: foetal fluids resorbed
foetal membranes shrivelled, uterus contracts
— In polytocous species, mummified foetus expelled at
parturition with no harm to live foetuses
— Develops in multiparous bitch, queen and sow
— Less common in uniparous species
Aborted fetus may be in state of autolysis or fresh depends on speed with which agent dispatches
fetus, and means by which pregnancy maintained. What happens to the species that are CL dependent in pregnancy?
— Pigs, goats
— Cows (up to 200 days)
— There can be a delay between time of death and lysis of CL
Aborted fetus may be in state of autolysis or fresh depends on speed with which agent dispatches
fetus, and means by which pregnancy maintained. What happens to the species that are CL independent in pregnancy?
— Ewes, mares
— Fetal death leads to cessation of fetal contribution.
Because P4 is produced by the placenta.
— Placental progesterone declines
— Fetus expelled in fresh state
. E.g, chlamydial enzootic abortion in ewes
In which species is mummification most common?
Sow
What are examples of pathogens causing different kinds of abortion?
Sows: — Porcine parvovirus Cows: - Bovine viral diarrhoea virus (BVDV) Ewes: - Toxoplasma gondli — Border disease virus
What does SMEDI stand for and what is it?
Stillbirths Mummification Embryonic Death Infertility
Characterises a number of viral infection in the sow and reflects different stages of development according to time they were infected.
— Will see a full-term litter consisting of small mummified fetuses ranging up to full-grown stillborn or live weakly piglets.
— Progressive infection along uterine horns in utero
— Abortion rarely occurs usually get mummification
. Often caused by porcine parvovirus or PRRS virus
What are common infectious agents of the mare that can cause abortion?
*Bacterial — cause placentitis Streptococcus zooepidemicus (most opportunistic pathogen) Escherichia coil (E. coil) Staphylococci *Fungal — cause placentitis aspergiIlus *ViraI — infect placenta & fetus equine herpesvirus-1 (EHV-1) equine arteritis virus (EAV)
What can happen to twin pregnancy in mare?
. one fetus is resorbed at an early stage OR
. one fetus is mummified at an early stage OR
. both twins are aborted, usually at mid to late gestation
How does the predominant source of P4
affect the speed at which a dead fetus is
aborted?
If it is CL dependent it is slower because it takes longer for the CL P4 to drop than if it is placental derived.
What are the common infectious causes of ovine abortion?
. Chlamydophila abortus: 37% — (enzootic abortion) . Toxoplasma gondii: 30% . Campylobacter species: 9% . Salmonella species: 6% . Listeria species: 4% . Schmallenberg virus
What does the schmallenberg virus do?
Late abortion or birth defects in in newborn sheep, cattle and goats.
Transmitted by insect vectors (Culicoides sp.)
If infected mid gestation neural system does not develop.
Chiamydial abortion is the main cause of ovine abortion in the UK. Abortion occurs in last 3 weeks of pregnancy
Placental damage from day 90 as colonised by bacteria, inflammation. Placental inflammation = Foetal death (usually fresh). What does the placenta look like?
Placenta:thickened areas between cotyledons & brownish exudate over surface.
Causes abortion storms.
Toxoplasma gondii is an intracellular protozoan
sheep are intermediate hosts.
Time of infection with Toxoplasma gondii
determines it’s impact of the foetus. Infection in which stage of pregnancy causes most damage?
— Early pregnancy +++ — Mid pregnancy ++ — Late pregnancy + . Lesions in brain, liver and kidney of aborted foetus
What does a placenta infected with toxoplasma gondii look like?
Dark red placental cotyledons with white speckles
of necrosis.
Strawberries!
How can campylobacter species that cause ovine abortion be identified on necropsy?
•Abortion in last 6 weeks of gestation and the birth
of live weak lambs
*Spreads rapidly due to organisms in aborted material
•No lessions present in placenta
Areas of necrosis sometimes seen in fetal liver
What are the two most common infectious agents that cause abortion in cows?
- Neospora species
* Bacillus lichenformis
Explain fetal immunocompetence with regards to BVD?
Fetal infection prior to the development of immunocompetence (at days 90 to 120) results in either fetal death or the development of a lifelong persistent infection where the animal is virus positive and antigen negative. By day 125, the immune system is becoming fully functional and infection after this time usually results in a competent immune response and subsequent elimination of the virus, so that at birth the calf is BVD antibody positive but antigen (virus) negative.
What are some of the non-infectious causes of pregnancy loss in the cow?
. Nutrition
— Deficiencies in vitamin A, selenium, phosphorous, copper
— Negative energy balance
— High intakes of rumen-degradable protein
. Toxic effects of blood urea or ammonia on the embryo
— Ingestion of dietary oestrogens/anti-oestrogens (g
clover)
. Stress
— High temperature and humidity
—fertilisation failure and early embryo mortality
— Other stressors associated with reduced fertility:
environment, psychological, high milk yield in early
lactation
. Timing of insemination
— Too late in oestrous period leads to ovum ageing and
embryonic death
. Conception too soon after calving
— High embryo loss likely due to poor uterine environment
What are some of the non-infectious causes of pregnancy loss in the sow?
Failure to establish pregnancy
— Unattached conceptuses susceptible to damage
— High incidence of late returns to oestrous
—Maternal recognition
Why are abortion rates high in angora goats?
— High metabolic demand for fibre production
. Nutritional stress
. Abortion occurs 90 — 120 days of gestation
. How can the same pathogen cause
different types of pregnancy loss?
And give an example of such a pathogen in
the sheep and the cow?
Timing. Infection at different times of
gestation.
Schmallenberg, toxoplasmosis, BVD
