UNL identifies new genetic defects in cattle

University of Nebraska-Lincoln (UNL) researchers have recently identified two new genetic mutations – delayed blindness in Herefords and bovine familial convulsions and ataxia (BFCA) in Angus cattle.

According to a UNL BeefWatch article by UNL Animal Science Breeding and Genetic PhD Candidate Rachel Reith, understanding and identifying genetic mutations allows beef producers to make breeding decisions to avoid producing cattle affected by these mutations. 

UNL researchers have spent years studying genomics to identify mutations and develop tests to help producers make informed decisions.

“The two most recently identified genetic mutations and the tools to address them will help producers make breeding decisions to reduce health issues caused by delayed blindness and BFCA,” says Reith.

These mutations were identified by producers who reported the issue to breed associations or local universities, who then contacted UNL. 

Herefords

Efforts between UNL researchers and the American Hereford Association (AMA) led to a commercial test for a new genetic condition – delayed blindness.

“The investigation began after several American Hereford’s were reported blind in both eyes, with presumed onset around 12 months of age,” Reith reports. “The cattle were normal as calves and had no obvious eye injuries. All of the blind cattle shared a common ancestor which appeared in each parent’s pedigree, leading to a suspected novel recessive mutation which causes the condition.”

In a recessive mutation, affected cattle need to inherit two copies of the mutation – one from each parent, who are related through a common ancestor.

Reith states, “To find the recessive mutation, deoxyribonucleic acid (DNA) samples from affected cattle, their dams and sires were collected with cooperation from the AHA. Samples from unaffected and unrelated cattle were used as controls. DNA samples were sequenced to look for mutations shared among the affected cattle but were not present in unrelated, normal cattle.”

UNL researchers found a recessive mutation fitting the criteria in a gene associated with a condition causing progressive blindness in humans – juvenile neuronal ceroid lipofuscinoses (JNCL). 

The Nebraska Veterinary Diagnostic Center (NVDC) and collaborating board-certified veterinary ophthalmologists performed eye exams and histopathology which determined the retinas of these cattle were degenerating similarly to human JNCL.

The investigation determined carriers of the delayed blindness mutation appeared normal, but DNA samples from additional cattle, including Hereford, Angus, Simmental and crossbred cattle, confirmed only Herefords who were descendants from the identified common ancestor carried the mutation. 

Since the mutation is recessive, it was spread unknowingly by unaffected carriers until affected cattle were produced by carrier mating.

With enough evidence, the novel mutation is causing delayed blindness, and a genetic test was developed for commercial use, allowing producers to help manage the delayed blindness mutation within herds to prevent mating of carriers.

Angus

Not all novel cattle mutations become prevalent in a breed, but genetic analyses help detect and understand the issue. 

According to Reith, with collaboration between Texas A&M  University Professor and Extension Veterinary Specialist Dr. Tom Hairgrove and Dr. Jon Beever, professor and director of animal science at the University of Tennessee, UNL researchers were able to identify a dominant mutation causing bovine familial convulsions and BFCA in a single Angus herd.

The founder had a single copy which he passed on to half of his offspring, and calves who inherited the mutation experienced seizures and were unable to thrive. 

Through genetic investigation, researchers discovered the mutation was only in affected calves and their sire, though the sire was seemingly unaffected himself. 

UNL research concludes sometimes dominant mutations cause a less severe condition or none in some animals but can be detrimental to their offspring, and it is possible the sire may have “outgrown” issues as a calf, which would be unknown to a producer who purchases the sire after weaning.

“Dominant conditions such as BFCA are often detected sooner than recessive ones, such as delayed blindness, due to their notable effect in the first generation,” states Reith. “Although the sire was culled early on due to the frequency of affected calves he was producing, the investigation provided answers for the producer as to why this occurred.”

Importance of genetics

Genetic research like the cases studied by UNL helps producers avoid matings which may result in calves failing to thrive or have other issues detrimental to their well-being or productivity.

In the BFCA example, genetics can provide answers when many calves from a single calf crop have a similar, detrimental condition.

It’s important to note these issues can be investigated only if they are reported to a breed association so the breed association can track and identify an emerging issue. 

Many breed associations work with UNL and the NVDC to determine if the issue can be attributed to an environmental cause such as exposure to a toxin, viral infection or a nutritional deficiency. 

If an environmental cause is not identified, UNL researchers consider genetic conditions, as in the case of delayed blindness and BFCA.

Through genetics, detrimental mutations can be managed to improve herd performance while avoiding unfavorable genetic conditions.

Melissa Anderson is the editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.