CAE (caprine arthritis encephalitis) is a chronic viral disease in goats that causes swollen, painful joints in adults and brain inflammation in young kids. There is no cure and no vaccine. Once a goat is infected, it carries the virus for life, though some animals never show obvious symptoms. CAE is one of the most economically significant diseases in the goat industry worldwide, reducing milk production, shortening productive life, and increasing vulnerability to other illnesses.
How CAE Spreads
The primary route of transmission is from doe to kid through infected colostrum or milk. A newborn kid nursing from an infected mother can pick up the virus within hours of birth. This makes the first feeding the single highest-risk moment for transmission in most herds.
Horizontal spread between adult goats also occurs but is less efficient. Prolonged close contact, shared housing, and nose-to-nose interactions over weeks or months can pass the virus between animals. The risk increases with herd density. Studies of Hungarian goat herds found that medium and large herds (over 50 animals) had herd-level prevalence rates above 74%, while smaller operations had significantly lower rates. Within infected herds, the average prevalence among individual animals reached 58%.
The Five Forms of the Disease
CAE can affect several body systems, and different goats may develop different forms of the disease. Many infected goats remain apparently healthy for months or years before signs appear.
Arthritis
This is the most common and recognizable form. Adult goats develop progressively swollen, stiff joints, especially the knees (carpi). Over time the swelling becomes firm and permanent as the joint lining thickens and fluid accumulates. Affected goats lose weight, move reluctantly, and may kneel to eat or graze. The arthritis is not reversible and worsens with age.
Encephalitis
This form strikes kids, typically between 2 and 6 months of age. The virus inflames the brain and spinal cord, causing weakness in the hind legs that progresses to paralysis. Kids may tilt their heads, circle, or lose coordination. Encephalitis progresses over days to weeks, and most affected kids do not survive.
Mastitis
CAE can cause a distinctive udder condition sometimes called “hard bag.” The udder becomes firm and swollen before or at kidding, but produces little or no milk. Unlike bacterial mastitis, there is usually no heat, redness, or foul-smelling discharge. The firmness comes from chronic inflammation of the mammary tissue itself. Does with this form often cannot nurse their kids adequately.
Pneumonia and Wasting
Some infected goats develop chronic respiratory disease or simply lose condition over time despite adequate nutrition. These forms are harder to pin on CAE specifically because the symptoms overlap with many other conditions, but they contribute to the overall economic toll of the virus in a herd.
Economic Impact
CAE’s damage goes well beyond the individual animal showing symptoms. Infected herds experience decreased milk production, shorter lactation periods, elevated somatic cell counts (which reduce milk quality), slower growth rates in kids, reproductive problems, and increased susceptibility to other infections. Goats with clinical disease are often culled years earlier than healthy herd mates. For dairy goat operations in particular, the cumulative losses from reduced milk yield and premature culling can be substantial.
Testing and Diagnosis
Two blood tests are widely used to detect CAE antibodies: the AGID (agar gel immunodiffusion) test and the ELISA. Most diagnostic labs now offer ELISA testing, which can be run on individual or pooled samples. The AGID test is considered more specific (fewer false positives) but less sensitive (more likely to miss infected animals) compared to ELISA. Both are reliable enough for herd control programs.
One important limitation: the virus can take months, not weeks, to trigger a detectable antibody response after infection. A goat that tests negative may still be in the early stages of infection. For this reason, testing once is not enough. Herds pursuing CAE-free status typically test every 6 to 12 months.
Kids under 90 days old present a special challenge. A positive test at that age usually reflects antibodies passed from the mother through colostrum, not an active infection in the kid. Testing kids before 90 days gives unreliable results.
PCR testing, which detects viral genetic material directly rather than antibodies, is also available but comes with its own trade-offs. False positives can occur if the test amplifies unrelated DNA sequences, so PCR results typically need additional confirmation steps. It is most useful in research settings or when antibody tests give ambiguous results.
Treatment Options
There is no antiviral treatment for CAE and no vaccine to prevent it. Once infected, a goat carries the virus permanently. Management focuses on keeping affected animals comfortable. Anti-inflammatory medications can help with joint pain, and good hoof care and soft bedding reduce stress on arthritic joints. Ensuring easy access to food and water matters as mobility declines. Some goats with mild arthritis remain productive for years with attentive care, while others deteriorate more quickly and need to be culled for welfare reasons.
Preventing Spread in Your Herd
Because there is no treatment, prevention is everything. The cornerstone strategy involves breaking the colostrum transmission cycle. Kids are removed from their dams immediately at birth, before they nurse. They are then fed either heat-treated colostrum or colostrum from a CAE-negative doe.
Heat-treating colostrum requires precision. According to Iowa State University Extension, colostrum should be heated to between 133 and 139 degrees Fahrenheit and held at that temperature for one full hour. This inactivates the virus while preserving the antibodies the kid needs. If the temperature exceeds 140°F, the proteins denature, the colostrum turns into a thick pudding-like consistency, and its protective value drops sharply.
Beyond colostrum management, controlling CAE requires a testing and segregation program. All goats in the herd should be blood tested, and seropositive animals either separated into a distinct group or culled. New animals entering the herd should be tested before introduction, ideally twice several months apart to account for the slow seroconversion window. Keeping positive and negative groups from sharing pens, feeders, or water sources reduces horizontal spread.
Many breeders now advertise “CAE-free” or “CAE-prevention program” status. If you are purchasing goats, ask for recent test results and inquire about the herd’s testing history. A single negative test is less meaningful than a documented pattern of herd-wide testing over multiple years.