Pregnancy failure Flashcards
What is meant by early embryonic death?
- Pre-implantation phase
- Before foetal-maternal recognition of pregnancy
- Does not involve elongation of life of CL (PgF2a released by endometrium)
What is meant by late embryonic death?
- Peri-implantation phase
- Occurs after life of CL has been extended
- Luteotrophic factor (MRP) has been released
What is meant by abortion?
- Post-implantation phase
- After organogenesis (organs formed, ossification)
- Material to to be born
When does maximal embryonic wastage occur in cows?
- Days 8-18 after insemination
- Late mebryo mortality occurs days 21-42
What occurs in the first 21 days post-insemination in the cow?
- Fertilisatoin
- Early embryogenesis
- Maternal recognition of pregnancy
What occurs at around day 21 in the cow in terms of pregnancy?
- Placentomes visible, contact between endometrium adn allantochorion
- Prior to this placenta is diffuse
What is the main form of embryo wastage in the cow?
Early embryonic death (before day 21)
What is meant by embryonic death in the horse compared to foetal death?
- Embryonic: before 40d gestation
- Foetal: after 60d gestation
In the mare, what percentage of embryo loss occurs
a. before maternal recognition (early)
b. before 40d gestation
c. later than 60 days
a. 5-24%
b. 8-17%
c. 10%
What are the two types of foetal death in the mare?
- Early (before d150)
- Late (after d150)
What are the two types of early foetal death?
- Type 1
- Type 2
Describe type 1 embryonic death in the mare
- Early embryonic death after maternal recognition
- 15 days
- Persistence of CL and prlonged luteal phase
- Treat with prostaglandin
Describe type 2 embryonic death in the mare
- Foetal death after endometrial cup formation at 36 days
- Lasts until demise of endometrial cups (90-150 days)
- Endometrial cups secrete eCG which is luteotrophic
- Maintian primary CL and form and maintain accessory CLs
- No treatment, wait for cups to complete cycle
List some causes of embryonic/foetal loss
- Chromosomal abnormalities
- Nutrition
- Environmental
- Physiological
- Infectious agents
- Insemination
- Trauma
Describe chromosomal abnormalities as a cuase of embryonic/foetal loss
- Inevitable
- In monotocous species causes early embryonic loss with return to service
- In polytocous, loss of chromosomally abnormal butkeep normal ones
- May be inhereted or arise de novo through gametogenesis, fertilisation and early embryo cleavage
- Abnormal meiosis, polyspermy, failure to extrude polar bodies
- Less likely in animals than humans as select for high fertility and ability to carry to term
What is meant by fertility?
The ability to conceive and become pregnant, not ability to maintain pregnancy
Give an example of a nutritional deficiency that may lead to embryonic/foetal loss
Vitamin A and E deficiency in cows and pigs especially
Give examples of environmental factors that may lead to embryonic/foetal loss
- Climate
- Stress
- Teratogens
What are teratogens?
Environmental factors that induce foetal abnormalities during developmental process, early embryo very susceptible, become sensitive again during CNS and CRS development
Give examples of physiological factors that may lead to embryonic/foetal loss
- Ovulation rate
- Uterine environment - asynchrony of uterus, ovary and embryo
- Immunological (recognition of embryo as foreign body)
- Endocrine
- Failure of maternal recognition of pregancy (lack of preogesterone, esp cows)
Outline how insemination may lead to embryonic/foetal loss
- Semen quality - may affect fertilisation/embryo quality
- Given in error during early pregnancy, may cause embryo loss
Outline how trauma may lead to embryonic/foetal loss
- PD by rectal palpation after 42 days
- Palpation of uterus can cause substantial embryo mortality if performed in early pregnancy
How may things prior to fertilisation result in embryo mortality?
- Environmental influences affecting folliculogenesis
- May influence quality of embryo derived from that oocyte
Give the proportion of causes of equine abortion (non-infectious, infectious, unknown)
- Non-infectious 70%
- Infectious 15%
- Unknown 15%
How may pregnancy loss result in pseudopregnancy?
- Maternal recognition of pregnancy
- Failure of CL regression
- Progesterone secretion continues
- Pseudopregnancy maintained
- Usually longer than normal pregnancy, as no parturient signal for luteolysis
What causes hydrometra in goats?
- Fertilisation followed by embryonic death
- CL persists
- Accumulation of sterile secretions
Explain how pathogens may enter the pregnant uterus
- Cervix - ascending infections, can occur with cervical incompetence or competent cervix (commensal or venereal)
- Systemic infection
- Pathogens affecting CL e.g. Infectious Bovine Rhinotracheitis (IBR)
What is the main bacterial cause of early embryonic death in cattle?
Campylobacter foetus var. venerealis
What is the main protozoan cause of early embryonic death in cattle?
Tritrichomonas foetus
What is the main bacterial cause of early embryonic death in horses?
Taylorella equigenitalis (CEM)
How are agents causing infection and early embryonic death introduced into the reproductive tract?
Via spem i.e. are venereal
What are common infectious agents causing abortion
- Bacterial
- Parasitic
- Fungal
- Viral
Outline the clinical signs of early embryonic death
- Tissues resorbed
- Animal returns to oestrus
Outline the clnical signs of death followig infection
- Pyometra may follow
- Cattle: CL persists, closed cervix and pus accumulation
Outline the clinical signs abortion
- Expulsion of abortus tissue
- Lysis of CL
- May be in state of autoysis or fresh depending on speed with which agent dispatches foetus and means by which pregnancy is maintined
Outline the appearance of papyraceous mummification
- Foetal fluids resorbed
- Foetal membranes shrivelled
- Uterus contracts
Describe foetal mummification in polytocous species
- Mummified foetus expelled at parturition with no harm to live foetuses
- Develops in multiparous bitch, queen and sow
Outline abortion in species what CL dependent pregnancy
- Pigs, goats, cows up to 200 days
- Delay between time of death adn lysis of CL
- Autolysis likely to occur (e.g. bovine herpesvirus 1)
- Mummified calves have unusual appearance
Describe the appearance of mummified calves
- Fluid resorbed
- Foetus and membranes covered in viscous chocolate coloured material
- Haemorrhage of caruncles is a consequence of abortion
Describe abortion in CL independent pregnancy
- Ewes, mares
- Foetal death leads to cessation of foetal contribution
- Placental progesterone declines
- Foetus expelled in fresh state immediately following death
Describe foetal death in twin pregnancy in teh mare
- One foetus grows more slowly than the other, smaller
- Smaller dies and if other survives then dead will mummify
- Will be delivered at term with llife foal
Outline the treatment of prolonged gestation in cattle
- Treat with PG to stimulate expulsion
- Must be sure foetus is expelled to prevent foetal maceration
- Bacteria enter uterus, digest soft tissues leaving bones
- Bones embedded in uterine wall = endometritis and endometrial damage (slaughter)
Give a key example of a pathogen of sows causing abortion
Porcine parvovirus
Give key examples of pathogens causing abortion in cows
- Neospora caninum
- Bovine viral diarrhoea virus (BVDV)
Give a key examples of pathogens in ewes causing abortion
- Chalmydial enzootic abortion
- Toxoplasma gondii
- Border disease virus
What is SMEDI?
Stillbirths, mummification, embryonic death, infertility in teh sow
- Characterises a number of viral infections in the sow
Describe the classical signs of SMEDI infection
- Full term litter with small mummified foetuses (closer to uterine body) and full-grown stillborn or live weakly piglets (at ends of horn)
- Progressive infection in utero along horn
- Abortion rarely occurs
What are common causes of SMEDI in sows?
- Porcine parvovirus
- PRRS
- Less frequently by enteroviruses
Give common bacterial agents of abortion in the mare
- Streptococcus zooepidemicus
- E. coli
- Staphylococci
- Mostly opportunistic
Give a common fungal agent of abortion in the mare
Aspergillus
Give common viral agents of abortion in the mare
- Equine herpesvirus-1 (EHV-1)
- Equine arteritis virus (EAV)
Describe the mechanisms of pregnancy failure in a mare with multiple conceptuses
- Placenta is epitheliochorial
- Conceptuses reliant on nutrition from entire surface
- 2 embryos, not enough nutrients for each
Describe the manifestations pregnancy loss in twin pregnancies in the mare
- One foetus resorbed at an early stage
- One foetus mummified at an early stage
- Both twins aborted, usually mid to late gestation
List common infectious causes of ovine abortion
- Chlamydophila abortus
- Toxoplasma gondii
- Campylobacter species
- Salmonella species
- Listeria species
- Schmallenberg virus
Describe Schmallenberg virus
- Late abortion or birth defects in newborn sheep, cattle and goats
- Milk disease in adults (milk drop, pyrexia, diarrhoea)
- Transmitted by insect vectors
- No evidence of zoonosis
- Foetal deformities vary depending on when infection occured during pregnancy
List signs of Schmallenberg virus in newborn sheep
- Hydrancephaly - often seen as deformed head but may appear nromal but unable to stand/suckle
- Born with flexed forelimbs, overlong fixed hindlimbs, twisted spine, abnormally flexed deformed legs (arthrogryposis)
- Bracynathia inferior (undershot jaws, parrot jaw)
- Prevents priming of muscles so unable to stand
During which period are sheep and cattle most sensitive to Schmallenberg virus?
- When the CNS is developing
- Cattle: 3-5 months
- Sheep: 2-3 months
Discuss vaccination against Schmallenberg virus
- 3 vaccines: Bovilis SBV, SBVvox, Sulvac SBV
- All inactivated virus vaccines
- Uptake by farmer low
- None currently available
Describe Chlamydial abortion in sheep
- Main cause of ovine abortion in UK
- Last 3 weeks of pregnancy
- Placental damage from day 90 colonised by bacteria, inflammation
- Causes abortion storms (over 30% of ewes)
- Housed, intensive flocks
- Immune mechanism protecting mother does not control once in placenta
- Nutrition limited during gestation
- High levels of organisms present in abortio products, contamination of envronmetn and other ewes
Describe the signs of Chlamydial abortion in sheep
- Lambs weak, susceptible to other infections, low survival
- Placenta has thickened areas between cotyledons and brownish exudate over surface
Give important features of Chlamydial abortion control
- Isolate aborted ewes and aborted material
- No cross fostering of lambs as will pass infection from ewe to new lamb
- Vaccines available
Describe Toxoplasma gondii
- Intracellular protozoan
- Sheep intermediate hosts
- Infection by ingestion of oocysts in food, water etc
- Time of infection and infective dose detemines impact on foetus
What is the effect of Toxoplasma gondii in early, mid and late gestation
- Early: large damage
- Mid: medium damage
- Late: low damage
Describe the features of abortion due to toxoplasma gondii
- Lesions in brain, liver and kidney of aborted foetus
- Resorption, barrenness, mummification, stillbirth, abortion, live lambs all possible outcomes
- Dark red placental cotyledons with white speckles of necrosis
- Gritty texture of cotyledons
Describe Campylobacter as a cause of abortion in sheep
- Abortion in last 6 weeks of gestation
- Birth of live weak lambs
- Spreads rapidly due to organisms in aborted material
- No lesions present in placenta
- Areas of necrosis in foetal liver (white rings)
Describe non-infectious pregnancy loss in ewes
- Low incidence
- Not usually detected until day 90
- Associated with multple rather than single conceptions
- Incidence of early embryonic death 20-33%
- May be due to ingestion of phytoeostrogens
- Structure defects of genital organs (limited cause)
List common agents causing abortion in goats
- Most agents causing abortion in sheep will also cause abortion in goats
- Toxoplasma
- Chlamydophila species
- Listeria species
- Coxiella species
Compare enzootic abortion in sheep and goats
- In goats infection and abortion can occur in the same year
- In sheep, abortion will occur the year after infection
Outline non-infectious pregnancy loss in goats
- Habitual abortion in most breeds, aborters usually culled
- Angora goats have high abortion rates due to high metabolic demand for fibre production, causing nutritional stress and hypoglycaemia (abortion 90-120 days of gestation)
Describe habitual abortion in goats
- Genetically determined hyperactivity of maternal adrenal cortex
- Initiates parturition
- Foetuses dead and oedematous
What is the most common cause of abortion in cows?
Neospora caninum
List important causes of abortion in cows
- Neospora spcecies
- Bacillus lichenformis
- Arachnobacter pyrogenes
- Salmonella dublin
- BVD
- Other (nutrition, stress, timing of insemination/conception)
Describe the effects of gestation age at time of infection with bovine BVD
- Early: <100 days, abortion, mummification, or in few cases stillborn or alive, virus +ve
- Mid: 90-125+ days, abortion, mummification, cerebellar hypoplasia, ocular/retinal lesions, epidermal lesions, other defects, virus +ve, Ab -ve
- Late: >150 days, term calf, normal development, virus -ve, Ab +ve, persistently infected, can become cytopathic
List major causes of non-infectious pregnancy loss in the cow
- Nutrition
- Stress
- Timing of insemination
- Conception toosoon after calving
Describe nutrition as a cause of non-infectious pregnancy loss in the cow
- Vitamin deficiencies in vit A, sleenium, phosphorous, copper
- Negative energy balance
- High intakes of rumen-degradable protein (high urea or ammonia in blood)
- INgestion of dietyar phytooestrogens
Give examples of stress that may cause abortion in cows
- High temp and humidity - fertilisation filaure and early embryo mortality
- Environment, psychological, milk milk yield in early lactation
How does timing of insemination affect abortion in cows?
Too late in oestrus period leads to ovum ageing and embryonic death
How does conception too soon after calving lead to abortion?
High embryo loss likely to due poor uterine environment
In the sow, what groups can pregnancy failure be divided into?
- Failure to establish
- Failure to maintain an established pregnancy
Describe failure to establish pregnancy in sows
- Unattached conceptuses susceptible to damage
- High incidence of late returns ot oestrus
- Can be due to lack of maternal recognition, stress e.g. gilt aggression, infection
- Infection most likely cause
What are the sensitive periods during which a pig conceptus is more likely to react to an adverse agent?
- Pre-attachment: before days 13-14
- Embryonic: days 14-35
- Foetal: after day 35
How does ovulation rate correlate to emrbyo survival in the sow?
- Negative correlation
- Increased ovulation rate leads to decreased embryo survival
- Increased competition for uterine space
Outline how nutrition affects embryo survival in the sow
High energy levels post service reduce embryo survival
Outline the effect of stress on embryo survival in the sow
- Increased stess reduces survival
- Temperature, management etc
- Avoid moving sows
Give examples of intrapartum factors that affect embryo survival in the sow
- > 20 mins between births
- Litter size: most deaths in last 3rd of litter due to secondary uterine inertia
- Older sows with more than 5 litters have increased intra-partum death
- Weight of sow
- Environmental stress - Temperaure, small farrowing crates
Give examples of post-partum factors that lead to neonatal death
- Mostly overlaying or chilling
- Lactation shorter than 3 weeks markedly increases piglet mortality
Give the main causes of pregnancy wastage in the bitch
- Abnormal uterine environment e.g. cystic endometrial hyperplasia
- Foetal defects
- Progesterone deficiency
- Infectious agents
What is the main cause of pregnancy wastage in the queen?
Progesterone deficiency
- Little evidence of abortion being a clinical problem in queen
Describe how sheep become infected with Chlamydia
- Ingestion/inhalation of infectious material
- Tonsil lymphoid tissue is primary site of infection, spreads via blood to caruncles then to placenta
What diagnostic tests can be used for Chlamydia
- Serological testing
- Aborted material
- post-mortem of lambs
- Bacterial cultre from swab
- Examination of fresh placenta
- Ziehl-Neelson staining of placenta
