Principles of Pregnancy Failure Flashcards
Consider what the important consequences of abortion and pregnancy failure in companion and production animal species are. List 3 key consequences and indicate for which common domestic species these consequences are particularly relevant. For example: Reduced milk production (dependent on timing of abortion); dairy cattle, goats and sheep. (5)
- Reduced production efficiency (reduced number of offspring per year): pigs, beef cattle, sheep, high genetic merit cattle (ET), (pedigree) breeders any species
- Emotional distress owner: any species but perhaps considered most important in companion animal owners
- Clinical disease animal: uterine infection may occur post abortion, depending on cause of pregnancy failure/abortion
- Disease after loss - e.g. infection, retained fetal membranes - this could affect all species to varying extents
- Loss of pregnancy after day 35, after endometrial cups have developed, can cause the horse to go into anoestrus
- Financial implications - may have paid for the animal to go to stud, such as horses and dogs, and then money loss in farm species due to reduced milk yield, maybe early slaughter or one less animal to send to market etc
Concerning the general causes of abortion and pregnancy failure in animals; what would be the approximate distribution of non-infectious, infectious and unknown causes?
The correct answer is: 70% non-infectious, 15% infectious, 15% unknown
Give examples of non infectious causes of abortion (7)
· inherited/congenital defect, arised during gametogenesis, fertilisation and early embryo cleavage
· nutrition (iodine deficiency)
· stress (too high/low temperature, photoperiod length, housing, stocking density)
· iatrogenic (AI of a pregnant cow, PGF2a injection when pregnant causing luteolysis)
· insufficient luteal function to support a pregnancy
· twins
· concurrent disease causing pyrexia
Why are there not more non-infectious causes identified if non-infectious causes of abortion are so common?
Non-infectious causes often occur early on in gestation and go unnoticed, if early embryonic loss occurs (i.e. before maternal recognition of pregnancy has taken place) the animal may return to her normal oestrus cycle.
The animal may not be showing any worrying clinical signs that the farmer would present to the vet?
Non-infectious causes could often be down to management issue, and also the vet would advise on this and then is likely to be resolved to an extent if this was the cause, so would not be submitted to the database. Non-infectious causes do not pose as much of a threat as infectious, so farmers may not feel it necessary to submit it as it will not help with the spread of disease or his neighbouring farms.
What are the common causes of pregnancy failure in horses? (5)
Bacterial, fungal – cause placentitis: i.e. Streptococcus zooepidemicus, Escherichia coli, Staphylococci
Viral – infect placenta & fetus: equine herpesvirus-1 (EHV-1), equine arteritis virus (EAV)
What are the common causes of pregnancy failure in dogs/cats? (12)
Split into infectious and non infectious
Infectious examples: adeno, parvo, herpes, distemper, leukemia, FIP, Chlamydia psittaci, Toxoplasma gondii
Non-infectious examples: abnormal uterine environment, foetal abnormalities, low progesterone
To establish the cause of pregnancy failure and abortion, we first need to collect the relevant history, what areas do we need to consider? (6)
· Biosecurity: Recent purchased animals/homebred replacements/hire bulls
· Method of service (AI, natural mating)
· Housing/management: feed types and quality, mixed age groups
· Fertility performance in other animals in the herd/flock
· Vaccination status, previous disease history
· Parturition: degree of assistance (mainly when issues with stillborns are identified)
A full clinical examination of the animal that aborted is the next step, including assessment of body condition in the herd/flock. During this examination samples can be taken which may help confirm/support your most likely differentials: a blood sample is easy to collect. It can be useful to examine a group of non-aborting and aborting animals and collect samples from both groups; a difference in exposure against certain pathogens such as IBR or Neospora may help to support your diagnosis. When the expelled fetus is available this can be your most important resource for diagnosis; if possible submit the whole fetus, with placenta and a blood sample of the dam to the diagnostic lab. When it is not possible to submit the whole fetus you can submit parts of it, dependent on your most likely differential diagnosis. Further guidance can be found in Livestock & Wildlife Disease Diagnosis at APHA or by phoning the lab, the material requested often depends on the diagnostic facilities, which may differ per lab.
You have to manage the expectations of your client (and yourself) when submitting samples to identify the cause of abortion or pregnancy failure; the diagnostic success rate is only 30%!
Why is the diagnostic success rate so low?
Establishing causation is complicated; finding (antibodies against) pathogens in the dam or fetus do not confirm they are the cause of abortion, it only confirms the animal has been exposed to that pathogen. So, you will need additional (for example histopathological) evidence to support your diagnosis.
The submitted material is incomplete; only part of the fetus is available and no placenta was submitted, or a blood sample form the dam. The lab needs all different aspects to identify not only the presence of a pathogen but also the cause of death of the fetus.
The quality of the submitted material is poor; dependent on the speed with which the pathogen dispatches the fetus and the method by which pregnancy is maintained in the various species, some fetuses are fresh when expelled, and others are autolysed. Foetal death leads to cessation of the foetal contribution and placental progesterone will decline, causing the fetus to be expelled in a fresh state (i.e. ewe, mare). When the pregnancy is CL dependent there will be a delay between the time of death of the fetus and lysis of the CL, during which time autolysis of the fetus will occur (i.e. cattle, pigs).
Submitting a complete set of samples within 6 hours after expelling the fetus will significantly improve the abortion diagnostic success rate.
Non-infectious causes are the most common cause, so not always able to be tested for or found!
When looking for infectious causes, and you find antibodies to a certain disease, it is difficult to know if the dam has been exposed before through things such as vaccination or if it is actually infected - and how can we be sure that’s the cause. Not everything has DIVA potential
If you only submit parts of the fetus - how do we know this is the right part? Different diseases require different tissues to isolate the correct things and do the corresponding tests - if the material is contaminated, or isn’t the right part of the animal, then the test cannot be done or will be unreliable.
What treatment would you advise for:
. A cow aborts because of a Salmonella dublin infection
Antibiotics and supportive treatment, particularly fluids either orally or in the vein, increase survival rates in calves and adults. Salmonella Dublin, unlike some other salmonellas is usually sensitive to most antibiotics. some, but not all, treated animals will become carriers, that is excrete Salmonella Dublin in their faeces for prolonged periods without ever showing signs of disease
What treatment would you use for
A cow aborts because she was inseminated 6 weeks after her first insemination
better management. why was pregnancy not picked before inseminated again? Better communication between the vet and the farmer, or between staff on the farm. Improve record keeping.
What treatment would you give for
A ewe aborts due to Toxoplasma gondii?
In the event of an outbreak, little can be done to prevent further spread since transmission is via contaminated food or water rather than sheep-to-sheep contact. Animals (especially cats) should be prevented from gaining access to sheep feed or bedding. Previously, monensin has been given in sheep feed in the lead up to lambing. Although this was shown to reduce perinatal lamb mortality related to Toxoplasma infection, monensin is no longer licensed for sheep and should not be used.
The best method of controlling ovine toxoplasmosis is therefore by vaccination. A live vaccine containing tachyzoites of the avirulent S48 strain is available. These tachyzoites do not cause pathology or form bradyzoites or tissues cysts. A single dose of vaccine is administered intramuscularly at least 3 weeks (and up to four months) prior to mating, from an age of five months. The vaccine is known to protect against toxoplasmosis for at least two lambing seasons
What treatment would you give for
A ewe aborts due to nutritional stress; inclement weather and insufficient feed have deteriorated the ability to maintain pregnancy?
better management, improved plane of nutrition. if bad weather and they are struggling, bring them in. Change this strategy ASAP to prevent it occuring in other ewes, but without causing stress. Pregnancy scanning so you can feed the twins and triples the right amount and not overfeed the singles.
What preventive strategies can be put in place to reduce the risk of abortion and pregnancy failure? (9)
· Good management (housing and nutrition)
· Monitor fertility performance (herd level parameters, levels of progesterone)
· Vaccination (vaccines available for Salmonella dublin, IBR, BVD, Leptospira, Coxiella, Blue tongue; the VMD product database will provide up to date information on vaccines available for all species). Be aware of the epidemiology of each pathogen though and the effect vaccination may have; does it eliminate or reduce clinical disease? Ensure your client can be compliant with the requirements of the vaccine (adhere booster times, correct storage and application etc)
· Biosecurity (live animals, semen, mechanical and biological vectors, fomites, aerosols)
· Correct plane of nutrition - e.g. pregnancy scanning ewes to ensure singles, doubles and triplets get sufficient amount.
· Practice good hygiene - biosecurity included
· Minimise stress
· Vaccination for what you can
· Use the database from earlier to look for the most common agents and reasons for abortion in your area, and apply this to your management strategy if it is of concern and something you can prevent
To finish this session, let’s think about zoonoses; earlier we mentioned the zoonotic risk of Toxoplasma; are there other zoonotic pathogens which cause abortion or pregnancy failure in animals that we need to be aware off? (5)
Infection of pregnant ewes with Chlamydia abortus may result in enzootic abortion of ewes. C. abortus may also cause abortion in goats and cattle.
Leptospirosis is caused by the spirochaete bacterium Leptospira interrogans, of which only some strains are pathogenic. L. Icterohaemorrhagiae is the main serovar causing human disease
Q fever is caused by the bacterium Coxiella burnetii. This can survive for long periods in the environment and is generally transmitted in aerosols or by fomites, including dust particles. Transmission to humans mostly occurs through exposure to aerosols containing C. burnetii. These may arise via bacterial shedding in products of abortion or normal parturition, or result from contaminated dust particles or bedding
Brucella - Brucella abortus has last been diagnosed in the UK in 2004, however surveillance still exists and farmers should be reporting each abortion to the APHA who will decide on further investigation. Follow the link for up to data regulations on Brucella.
Listeria monocytogenes is a bacterium that is widely distributed in the environment,
including in soil, decaying vegetation and fodder such as silage in which the bacteria
can multiply
