Improving the success rate of abortion diagnosis

Josepha DeLay, Murray Hazlett, Maria Spinato, Andrew Brooks, Jim Fairles

Identifying the cause of abortion in domestic animals is important so that measures can be taken to prevent additional losses and avoid significant economic impact at the herd or flock level. However, determining the exact cause of abortion can be a frustrating process for veterinarians, producers / owners, and veterinary pathologists. Some cases are the result of physiologic, hormonal, genetic, or other causes that may not produce morphologic lesions or be detectable by available diagnostic tests. Although the cause of abortion is unknown (idiopathic) for a proportion of abortions in all species, a routine approach to testing often allows at least broad categorization of the cause as infectious vs. non-infectious, and exclusion of many specific infectious agents.

The thoroughness of tissue sampling and diagnostic testing has a significant impact on the success rate of abortion diagnosis. Fetuses and placentas submitted intact to the diagnostic laboratory are examined by pathologists in a consistent manner, and a routine battery of microbiologic tests and histopathology are carried out based on the species and clinical history. This approach will identify the involvement of infectious agents and non-infectious conditions in a high proportion of cases.

We reviewed the diagnostic success rate of abortion cases by submission type, abortion submissions to the AHL from multiple livestock species in 2017 and 2018. ‘AHL postmortem (PM) submissions’ included those for which 1 or more fetuses, with or without placenta, were submitted for examination and diagnostic test selection by a pathologist. ‘Field / in-clinic postmortem (PM)’ submissions included those for which PM exam, sampling, and test selection was carried out by veterinary practitioners. Submissions for full PM by a pathologist made up the majority of abortion cases submitted to the AHL (Fig. 1). In all species, the frequency of a definitive or suspected (histologically compatible) etiologic diagnosis was higher for AHL PM submissions than for those cases in which samples were collected by field or in-clinic PM (Fig. 2). All swine abortion cases were submitted as AHL PM submissions, precluding comparison of results based on submission type for this species.

The advantage of a consistent, standardized approach to diagnostic testing of abortion cases is illustrated by these results. To increase the diagnostic success rate for abortion cases, veterinarians are encouraged to submit fetuses with placentas to the diagnostic laboratory for examination and testing. Alternatively, practitioners performing field or in-clinic PMs on abortion cases should conduct thorough exams with consistent sample collection and testing.

Recommended testing schemes for abortions in all species are listed in the AHL User’s Guide, available in print and online at . For cattle (and soon to follow for other species), more detailed information including sampling templates can also be found on the AHL website: . Veterinarians must also be aware of the risk of zoonotic disease transmission when performing field or in-clinic PMs, especially ovine, caprine, and bovine abortions, and appropriate safety precautions should be taken.

There is justifiable concern about the cost of carrying out a set panel of diagnostic tests on every abortion case, and indeed some judicious test selection can be used in specific cases depending on the herd situation. However veterinarians and producers must also consider the financial cost of not reaching a diagnostic conclusion.

 AHL PM vs. field / in-clinic PM (%).

Figure 1. AHL abortion submissions by species and sample type, 2017-2018: AHL PM vs. field / in-clinic PM (%).

 AHL PM vs. field/in-clinic PM (%).

Figure 2. Frequency of definitive or suspected abortion diagnoses by submission type, 2017-2018: AHL PM vs. field/in-clinic PM (%).