Calf Recumbency aka Early Onset Muscle Weakness Syndrome

In 2020, there were multiple calves found unable to stand at birth or shortly after and were then seen by veterinarians in Pennsylvania. Calves were either weak and unable to stand immediately after birth, could stand with assistance, or lost the ability to stand within the first two weeks of life.  Besides showing signs of muscle weakness, these calves became unthrifty, succumbed to secondary health problems, or were euthanized.  Researchers from Pennsylvania State University learned of similar cases of calves on farms in New York and Florida^1,2.  There have also been reported cases in Wisconsin.  

Trying to solve the mysterious calf condition

Veterinarians sought to determine what was affecting these animals. One possible cause was dystocia, which could have placed the calf in a low oxygen state that deprived the brain of oxygen, making it difficult for the calf to stand immediately after birth. Dystocia could have also resulted in injuries to the musculoskeletal system.  Another possibility was that calves conceived through in vitro fertilization or embryo transfer have been known to have extreme birthweights, be born premature, or not be fully developed, which could result in the calf’s inability to stand.  A third thought was an infectious disease such as bovine viral diarrhea virus could also cause the calf to be weak and unable to stand.  If the dam was infected with the protozoa neospora, she could transmit this to the calf in utero, which could affect the calf’s nervous system.  After much investigation, veterinarians could not determine a neurological, infectious, or metabolic reason for why these calves could not stand.  

A dive into genetics for answers

With no other likely causes, veterinarians turned to genetics to look for a gene defect.   Researchers from the U.S. Department of Agriculture’s Agricultural Research Service, the Council on Dairy Cattle Breeding, Dr. Chad Dechow from Pennsylvania State University, and many genetics companies worked to discover a defect on chromosome 16.  Researchers determined that affected animals had two copies of a mutation in the CACNA1S gene on chromosome 16³. 

The CACNA1S gene makes the main piece of a calcium channel found on the outside membrane of muscle cells.  The job of these CACNA1S calcium channels is to transmit the signal from the nervous system to the interior of the muscle to other calcium channels that cause muscle contraction, allowing the body to move.  Without CACNA1S calcium channels, the signal is not “forwarded” to the interior calcium channels, preventing the muscle from contracting and resulting in muscle weakness. 

Identified bull as an early-known carrier of the mutation

These researchers identified Southwind Bell of Bar-Lee as one of the earliest known carriers of the mutated allele.  In a 2009 article by Schlesser et al. they identified Southwind Bell of Bar Lee (bull 12 in the article) as having a bimodal distribution of his offspring for perinatal survival⁴.  This means that some of his offspring were likelier to survive than others.  Southwind’s most prominent descendants Roylane Socra Robust and Seagull-Bay Supersire⁵ have also been identified to have the mutated gene. While the prevalence rate of the mutated gene in the Holstein population is currently unknown, it is important to realize that the mutation has been traced back to some influential family lines.

Currently, bull studs are testing their AI bulls for the presence of this mutation.  Bulls identified as having this mutation are still used by some bull studs, while others have eliminated these genetics from their herds. If a bull stud decides to maintain bulls with this mutation, they are publicizing this information so producers can make informed decisions about bull use (Table 1)⁵.  If you have cows and heifers with similar pedigrees as the affected bulls, then it is not recommended to breed with affected bulls.  

Table 1: List of bulls and their Muscle Weakness genetic status.

The unique thing about this defect is that some animals with two copies of the mutated allele survive to adulthood. Winstar Geometirc-P (Table 1) is one such animal that has two mutated genes.  It is not known why some animals can survive, but management differences between farms is thought to be the reason³.

What does this mean for you and your herd? 

 This means that sire selection decisions are more critical today than yesterday.  While genetic testing is available through Feanix Bio for $10 a test, it can get costly to test your entire herd.  Breeding with bulls tested and shown to be free of the mutated gene will allow you to breed your heifers and cows without worry.  Keeping records of animals in your herd with either one or two copies of the mutated gene is key to ensuring you make good sire selection choices in the future to avoid offspring with two copies of the mutated gene. If you breed females to a bull with a mutated gene, it is important to ensure the female’s pedigree does not also have animals with the mutated gene present.  Having different ancestors helps to eliminate the possibility that the female has a copy of the mutated gene. Information on this mutation is still evolving as more animals with the defect are identified.

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