406.587.4531
simmental@simmgene.com
406.587.4531
simmental@simmgene.com
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.
TraitTrac
Hydrops Update: January 2025
All confirmed hydrops pregnancies thus far have been in WS All Aboard B80 (ASA# 2852207) daughters, All Aboard paternal granddaughters (daughters of All Aboard sons) or recipients of these embryos. Thus far, there is no evidence that healthy calves born to females with All Aboard in their pedigree are at risk.
Our hypothesis remains that this is a dominant mutation that is only expressed in a fetus that inherits the variant from the female parent. Following this hypothesis, if an All Aboard daughter or paternal granddaughter produces a healthy calf from a healthy pregnancy, that calf is genetically normal and safe for breeding. The dam of said calf may still be a carrier herself but the calf is likely free. All Aboard and his sons are at risk for silent transmission of the variant but do not directly produce affected calves. It is not necessary for the sire and dam to be related for the calf to be affected.
Early detection and termination of pregnancy is the best approach to prevent loss of the dam with the calf. Affected dams have dramatic abdominal enlargement during late gestation and when palpated the uterus is extremely distended and tense. Ultrasound of the pregnant uterus in affected dams may identify swelling of the uterine wall as early as 90 days of gestation, although this may not be apparent in all cases.
UNL Hydrops Research Update: January 2025
From: Dr. David Steffen, Dr. Matt Hille, and Dr. Jessica Petersen
The transfer of 25 embryos derived from cows that previously produced hydrops pregnancies resulted in 15 pregnancies. Of these, 4 were confirmed hydrops pregnancies, and one pregnancy that was terminated early was suspected to be in early stages of hydrops development. Regular monthly ultrasounds during gestation identified swelling of the uterus in some cows that were later confirmed to be hydrops cases. This ultrasound finding was not definitive in every case but did occur in cows before any outward signs of disease.
We (UNL) collected pathology data from these calves and from several other cases referred to the NVDC. This included DNA sequences, gene expression data, DNA methylation, and information on structural variation in the DNA. No causative marker has been identified at this point. We have identified genes expressed differently in affected calves compared to controls. Currently we are examining the activity of these genes at the protein level. This may allow us to more definitively affirm diagnosed cases and perhaps identify what is causing the observed physiologic changes. There is no anatomic change in the fetus that can identify affected calves by routine microscopy or necropsy. The medulla (center) of the kidney appears redder (congested) than in control calves. We suspect the defect impacts resorption of fluid by the kidney, and the fluid in the uterus to be in part excess dilute urine from the fetus.
Compared with nearly all other known cattle defects, hydrops occurs through a unique means of inheritance. Additionally, we expect the causative variation to be regulatory and not a mutation that “breaks” a gene by altering the gene sequence itself. Due to these characteristics, we remain grateful for reported cases and samples from affected calves, and we encourage submission of additional DNA samples of calves born to All Aboard daughters that were the result of normal pregnancies. Analysis of the extensive data files is in progress. The unusual mechanism of inheritance in this family frustrated the normal rapid gene discovery analysis we often experience with simple recessive gene variants.
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,
Archived Hydrops Updates
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.