Citrullinemia in Cows
- See your vet immediately. Citrullinemia is a rare inherited metabolic disease that can cause rapid neurologic decline in newborn calves.
- It is most closely associated with Holstein and Friesian lines and is caused by a recessive ASS1 gene mutation that disrupts the urea cycle.
- Affected calves are often normal at birth, then become depressed within hours to a day and may develop tongue protrusion, aimless wandering, head pressing, tremors, seizures, and death within a few days.
- There is no reliable curative field treatment for naturally affected calves. Care is usually supportive, while diagnosis and herd prevention focus on genetic testing and breeding management.
- If a calf shows sudden neurologic signs in the first days of life, your vet may also need to rule out septicemia, meningitis, toxicities, trauma, and other congenital disorders.
What Is Citrullinemia in Cows?
Citrullinemia in cows is a rare inherited disorder of the urea cycle, the pathway the body uses to convert ammonia into urea so it can be removed safely. In affected calves, a deficiency of the enzyme argininosuccinate synthetase (ASS1) prevents normal ammonia handling. Ammonia and citrulline then build up in the body and can quickly damage the brain.
This condition has been described mainly in Holstein and Friesian cattle. It is inherited in an autosomal recessive pattern, which means a calf must receive the altered gene from both parents to become affected. Carrier animals usually look healthy, so the problem can stay hidden in a herd unless breeding records and genetic testing are used.
Most affected calves appear normal at birth or for the first several hours of life. Then signs can progress fast, often over 1 to 5 days, with depression, abnormal behavior, poor coordination, and severe neurologic signs. Because the disease is typically fatal, early veterinary involvement is important for calf welfare, diagnosis, and herd planning.
Symptoms of Citrullinemia in Cows
- Depression or dullness in a newborn calf
- Poor nursing or weak suckle reflex
- Tongue protrusion
- Unsteady gait or incoordination
- Aimless wandering or abnormal behavior
- Frothing or excessive salivation
- Head pressing
- Tremors or convulsions
- Rapid progression to recumbency or death within days
See your vet immediately if a newborn calf becomes dull, stops nursing, seems disoriented, or develops any neurologic sign. Citrullinemia can look like ammonia toxicity, severe infection, meningitis, or other emergencies, and calves may worsen very quickly.
A calf that is head pressing, seizuring, unable to stand, or becoming unresponsive needs urgent veterinary attention. Even when treatment options are limited, prompt evaluation helps guide humane care, protect other calves by clarifying whether the problem is inherited, and support breeding decisions for the herd.
What Causes Citrullinemia in Cows?
Citrullinemia is caused by an inherited mutation in the ASS1 gene. This gene provides instructions for argininosuccinate synthetase, an enzyme needed in the urea cycle. When the enzyme does not work, the calf cannot process nitrogen normally, and ammonia accumulates in the bloodstream. High ammonia is toxic, especially to the brain, which explains the severe neurologic signs.
In cattle, the disorder is inherited as an autosomal recessive trait. That means both sire and dam must be carriers for an affected calf to be born. On average, when two carriers are bred together, about 25% of calves may be affected, 50% may be carriers, and 25% may be genetically clear. Carrier cattle are usually normal in appearance and performance.
The condition is most often discussed in Holstein and Friesian families. Because carriers can look healthy, the disease is best understood as a breeding and herd genetics issue, not something caused by feed, housing, or routine calf care. Pet parents and producers do not cause this disorder through day-to-day management.
How Is Citrullinemia in Cows Diagnosed?
Your vet will usually start with the calf's age, breed background, and pattern of signs. A Holstein or Friesian calf with severe neurologic signs in the first day or two of life raises concern, but citrullinemia is uncommon and other emergencies are often more common. Your vet may first work to rule out sepsis, meningitis, trauma, toxic exposure, congenital brain disease, and metabolic problems.
Diagnostic testing may include a physical exam, neurologic assessment, and basic bloodwork if available. Historically, affected calves have shown markedly increased citrulline, and the disease is associated with hyperammonemia. In practice, the most definitive antemortem confirmation is usually DNA testing for the ASS1 mutation, especially when breed history supports suspicion.
If a calf dies or humane euthanasia is needed, a necropsy can be very helpful. Postmortem findings, combined with breed history and genetic testing, often provide the clearest answer. Confirming the diagnosis matters because it helps your vet advise on whether the parents should be considered potential carriers and whether herd-level screening is warranted.
Treatment Options for Citrullinemia in Cows
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Farm call or clinic exam
- Assessment of calf comfort, hydration, and neurologic status
- Short-term supportive nursing care as directed by your vet
- Discussion of prognosis and humane endpoints
- Planning for postmortem testing if the calf declines
Recommended Standard Treatment
- Exam and neurologic evaluation
- Basic bloodwork where available
- Supportive care such as fluids and nursing support if your vet feels it is appropriate
- Targeted genetic testing for the ASS1 mutation or submission of samples through a diagnostic lab
- Necropsy and tissue submission if the calf dies or is euthanized
Advanced / Critical Care
- Referral-level hospitalization or intensive monitoring
- Expanded laboratory testing and repeated blood sampling
- Aggressive supportive care for seizures, recumbency, and metabolic instability as directed by your vet
- Specialist consultation when available
- Detailed herd genetics review and broader carrier-testing plan
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Citrullinemia in Cows
Bring these questions to your vet appointment to get the most out of your visit.
- Based on this calf's age, breed, and signs, how likely is citrullinemia compared with sepsis, meningitis, or another emergency?
- What tests can help confirm or rule out citrullinemia in this calf right now?
- Would genetic testing for the ASS1 mutation be useful in this case, and which samples do you need?
- If this calf's prognosis is grave, what are the most humane care options?
- Should we test the sire, dam, or related animals for carrier status?
- If this is confirmed, what breeding changes would reduce the risk of another affected calf?
- Would a necropsy add useful information for herd management if the calf dies or needs euthanasia?
- What cost range should I expect for calf testing versus herd-level carrier screening?
How to Prevent Citrullinemia in Cows
Prevention centers on breeding management, not calf care after birth. Because citrullinemia is inherited as a recessive trait, the key step is to avoid mating two carriers. If your herd includes Holstein or Friesian lines, especially with a history of unexplained newborn neurologic deaths, talk with your vet and breeding adviser about whether genetic screening makes sense.
Carrier testing is the most practical prevention tool. A DNA test can identify animals that carry the ASS1 mutation even though they appear healthy. In many herds, the goal is not necessarily to remove every carrier immediately, but to make informed mating decisions so carrier-to-carrier breedings do not occur.
Good records matter. Keep notes on affected calves, pedigree links, semen sources, embryo transfers, and any prior genetic test results. If a calf is suspected to have citrullinemia, confirming the diagnosis through genetic testing or necropsy can prevent repeated losses and help your vet guide a realistic herd plan.
This is a condition where prevention is often far more effective than treatment. Once a calf is clinically affected, the outlook is usually poor. Identifying carrier risk before breeding gives pet parents and producers the best chance to protect future calves.