Hydrops Information Center

The Hydrops Information Center is your source for the latest information and resources regarding the reported hydrops pregnancies in a line of Simmental cows. 


Background and Original Letter to Membership

The Nebraska Bovine Congenital Defects program recently recognized an increased number of reports of hydrops pregnancies in a line of Simmental cows. Reports involve daughters and granddaughters of the bull WS All Aboard B80, ASA #2852207, and pregnancies created by embryo transfers of daughters. Not all daughters or granddaughters have had problems; in fact many daughters of WS All Aboard B80 have had normal pregnancies. A small number of these daughters develop markedly enlarged abdomens in late pregnancy due to a dramatic excess of fluid in the fetal membranes (Figure 1 and 2). The complications of pregnancy with the condition usually results in loss of the calf and occasional loss of the dam. Early pregnancy termination will save the cow. Late-stage induction and attended birth may save the cow and calf. You should consult with your herd veterinarian for final determination of how to manage the pregnancy. 

Hydrops has several reported causes. There can be abnormalities in fluid metabolism in the fetus or problems in placentation affecting fluid exchange between the fetus and the dam. There is a genetic form described in Japanese Black cattle that affects the fetal kidney function. 

At present, a genetic cause is suspected although the pattern of inheritance is unknown. Epidemiologic features do not suggest a recessive genetic condition. The reported cases suggest a possible dominant variant that is sex-influenced and expressed in the fetus and/or placenta (conceptus) of some female descendants. Reports also suggest the hydrops condition was transferable through embryo transfer to affect pregnancies carried in unrelated recipient dams.

Currently, there have been no cases reported on the ancestors of WS All Aboard B80, so it may be a novel mutation within this sire. At present, using WS All Aboard B80 in a terminal program where all calves are harvested will likely result in normal pregnancies with normal calf growth and health. Until a test is developed, retaining heifers from WS All Aboard B80 carries a small but yet unknown level of risk of developing a hydrops pregnancy. 

The University of Nebraska–Lincoln researchers in coordination with the owners and breeder of the bull and the American Simmental Association are seeking active cases so that the definite cause can be determined. Producers with cows exhibiting symptoms should contact Bailey Abell at The American Simmental Association (406-587-4531; simmental@simmgene.com) or Dr. Steffen at the Nebraska Veterinary Diagnostic Center (402-472-1434, dsteffen1@unl.edu). ASA will arrange for sample collection and paperwork necessary to advance the research and determine solutions to attempt to prevent future cases. Samples from daughters in this line that have had multiple normal pregnancies carried to term and offspring from normal pregnancies are also of interest and serve as controls.

Typically, sampling will involve getting a blood sample in an EDTA (purple top) blood tube from the dam, and the calf if born alive. If the calf is not viable, collecting and freezing an ear for shipment is an alternative. An ear notch frozen from the cow can work, but EDTA blood is preferred. Capturing an image of the cow, and a veterinarian’s report to verify diagnosis is also helpful. Parentage records of the fetus in an affected pregnancy. For a few initial cases, collection of an entire fetus or fetal placental unit will help to determine the cause of the fluid buildup. Please also identify the gender of the calf from the affected pregnancy.

The DNA sample will be used to verify parentage and see if an identifiable genetic risk factor might be determined from DNA sequencing. The ability to develop a DNA test depends, in part, on quickly notifying the ASA regarding active cases in order to gather informative samples. Getting the DNA samples is critical to this work and reporting after the calf is lost and destroyed will not advance this research. Getting an affordable test to market will allow breeders to manage their selection and mating decisions with more accurate information.

 It should be noted that a growing body of evidence supports the hypothesis that a large proportion of animals carry one or more genetic mutations for unfavorable traits or conditions. These undesirable genetic variants simply go unidentified in most animals. Usually, these genetic conditions only come to light once animals are heavily used. WS All Aboard B80 was a heavily used bull due to the many beneficial attributes he possesses. It should be noted that he and his descendants still possess those attributes. The sooner a genetic test can be discovered to manage the genetic condition, the better we can progress with more informed decisions to leverage the positive attributes of All Aboard’s lineage.

An example of late gestation hydrops with a dramatic abdominal enlargement and easily recognized as abnormal. Supporting structures can stretch and the lower abdomen can drop. 

Early presentations may look like a twin pregnancy or a pregnant cow with moderate bloat. Veterinary examination may be necessary for early diagnosis.

Research Update

The ASA staff and University of Nebraska–Lincoln research team are working diligently to thoroughly document the pathology related to this condition to find a causative mutation that can be used for a DNA test. A large genotyping investigation has zeroed in on a region of the chromosome that is likely to contain the causative mutation. Continued investigation, sequencing, genotyping, and analysis is ongoing.

Late in 2023 another project was initiated that will track these pregnancies from conception through to the end of pregnancy to monitor fetal development, potential abnormalities with the pregnancy throughout gestation, and thoroughly document the Hydrops condition and sample collection. This research is ongoing with the pregnancies nearing three months along.

In addition to the above research, the ASA and UNL are collecting information and samples on active Hydrops cases. It is our sincere hope that we will find a DNA test as soon as possible in order to deliver more certainty and informed decisions to the operations with WS All Aboard genetics.


Hydrops has been added to Herdbook’s TraitTrac with WS All Aboard B80 listed as a documented carrier. At this time there are no genetic holds placed on his descendants as there is not a DNA test available yet. Once there is a test, then Hydrops will follow the same policy as other genetic conditions. 

Informational Webinar Recording

An informational hydrops webinar was held and recorded in May 2023. To view the recording and learn from Dr. David Steffan and Jessica Peterson of the Nebraska Bovine Congenital Defects program and ASA staff, click here.

Archived Hydrops Updates

February 2024 Hydrops Update

October 2023 Hydrops Update

ASA Recommended Marketing Statement for WS All Aboard B80 Descendants

For breeders marketing genetics related to the recent Hydrops condition traced to WS All Aboard B80 (ASA #2852207), the ASA has issued the following statement to explain the current understanding and risk associated with purchasing descendants of WS All Aboard B80:

Female progeny who are descendants of or are directly sired by WS All Aboard B80 (2852207) are at risk for carrying a genetic abnormality called Hydrops. Daughters may develop a serious condition during late gestation that results in excess fluid in the fetal membrane, which typically causes the loss of the calf and occasionally the dam. There is no test at this time to identify animals carrying this mutation. Research is ongoing regarding the transmission of the abnormality, and to develop a genetic test. Helping our producers navigate this issue is of the utmost importance to us. Therefore, given that there is neither a full understanding of this condition nor a test, careful consideration should be given regarding the question of whether to breed WS All Aboard B80 descendant females until more information is available to breeders.

If you have experienced a female in late gestation develop significant fluid build up within her uterus/fetal membranes, please fill out the brief questionnaire below and a team member will be in contact with you soon. Thank you.

If you have questions regarding hydrops, please contact Jackie Atkins at jatkins@simmgene.com or 406-587-4531.

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