Blog: Center for the Science of Animal Care and Welfare

False Pregnancy Phenomenon

clouded leopard at Brookfield Zoo

False Pregnancies: How do we deal with species who experience this phenomenon?
As the Endocrinology Lab Manager one of the best parts of my job is diagnosing pregnancies. And one of the most challenging aspects is diagnosing pregnancies in some of our animals with absolute certainty! I was glaringly introduced to false pregnancies over a decade ago while monitoring progesterone levels in our fennec fox female. Repeatedly her progesterone levels would increase and stay elevated indicating pregnancy, but no pups to be seen. I was shocked! Our fennec fox female had 4 false pregnancies in the span of 1 year. It appeared cyclical? These false pregnancies would last slightly longer than their typical gestation length of 50 days making it very hard to dismiss a pregnancy. We would prepare, wait, but no births.

Fennec Fox graph

Fennec Fox female false pregnancies.  Fecal progesterone metabolite (fP) levels mimic pregnancy profiles and occur every few months, lasting 2-3 months.  Fennec Fox gestation length is approximately 50 days.

Why is this happening?  How is this happening?  We immediately assumed there had to either be a hormone imbalance, illness, maybe even a benefit (or else, why do it?) could it even be psychological? The truth is we just don’t know the cause yet. This is an area of wildlife endocrinology that remains mysterious and we instead are focusing on how to analyze the hormones properly on species that may experience false pregnancies. 

In humans, it has been documented as mainly a psychological issue called pseudocyesis. A woman believes she is pregnant so strongly that the body responds by releasing hormones that trigger the symptoms of pregnancy, even in some cases labor pains…but no actual pregnancy. 

In domestic dogs this happens frequently as well but is documented as most likely a hormonal imbalance. There was a case examined in a tiger that experienced a false pregnancy and the conclusion was a medication given to treat IBS (irritable bowel syndrome) kick-started the process. The hormones progesterone and prolactin that sustain a pregnancy and assist in lactation, are secreted after an ovulation but there is no actual pregnancy. 

False Pregnancies in Other Species

So far we know false pregnancies can occur in some canines, bears, and most (if not all) feline species. This information has been published in peer-reviewed articles. Most of the time, false pregnancies are shorter than pregnancies though this was not the case in fennec fox. One of the main roles of zoos is to participate in breeding programs which makes diagnosing pregnancies correctly vastly important. The AZA’s (Association of Zoos of Aquariums) Species Survival Programs each have a Breeding and Transfer Plan which includes breeding recommendations that would ensure sustainability of the species in AZA zoos.

How do we avoid false-positive pregnancy results? A new assay was developed by the Institute for Zoo and Wildlife Research in Berlin, Germany and can be purchased from a company in the US.  This hormone assay measures PGFM, a hormone that will only increase if there is an actual pregnancy.  

Berlin researchers Finkenworth et al have begun testing this new PGFM assay to distinguish between pregnancy and false pregnancy.  Their first attempt with Iberian lynx was successful showing an increase in progesterone but no increase in PGFM indicating this animal is in fact not pregnant.

Researchers in Berlin have already tested this new assay on nearly 40 species of felids and in a majority of cases they were able to measure PGFM in pregnant individuals approximately 2/3 through their pregnancy, therefore, confirming the pregnancy.  We decided to add 3 more species to this research: Amur tiger, clouded leopard, and black-footed cat. 

Please stayed tuned for the results of this study next time from the Endocrine Lab!

-Jocelyn Bryant, Endocrinology Lab Manager

Posted: 9/18/2017 12:05:03 PM by Robert Sit

Center for the Science of Animal Care and Welfare



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