Bovine Leukosis (Lymphoma) in Cows

Bovine leukosis is a disease complex involving lymphoid cancer in cattle. In practice, people often use the term for enzootic bovine leukosis, which is lymphoma associated with bovine leukemia virus (BLV). There are also sporadic forms of lymphosarcoma that are not caused by BLV. Merck notes three sporadic patterns: juvenile, thymic, and cutaneous forms.

BLV is a blood-borne retrovirus that infects lymphocytes. Many infected cows remain outwardly normal for years. A smaller group develops persistent lymphocytosis, and fewer than 5% go on to develop malignant lymphoma. When tumors form, signs vary widely because they depend on which organs are affected.

This is why bovine leukosis can be confusing for pet parents and producers. One cow may look normal on routine testing, while another may show weight loss, enlarged lymph nodes, poor production, or sudden decline. Your vet can help sort out whether a cow is carrying BLV, has lymphoma, or has another condition that looks similar.

The most common infectious cause is bovine leukemia virus (BLV). BLV spreads mainly when infected lymphocytes in blood or tissues move from one animal to another. That means transmission risk goes up with practices that can transfer blood, including reused needles, contaminated dehorning or tattoo equipment, ear-tagging tools, castration tools, and some palpation or surgical procedures if hygiene is poor.

USDA APHIS describes BLV as a blood-borne infection and notes that the virus is common in U.S. cattle herds. Most infected animals never develop cancer, but a small percentage eventually develop malignant lymphoma or lymphosarcoma. Adult cattle, especially those 4 to 8 years old, are the group most often affected by enzootic bovine leukosis.

Not every bovine lymphoma case is caused by BLV. Merck Veterinary Manual also describes sporadic lymphosarcoma, which includes juvenile, thymic, and cutaneous forms. These are not linked to BLV infection. Your vet may need testing and sometimes tissue sampling to tell the difference between BLV exposure and true cancer.

Diagnosis usually happens in two parts: testing for BLV infection and confirming whether lymphoma is actually present. For herd screening, your vet may start with ELISA testing on serum or milk. USDA APHIS lists AGID, ELISA, and PCR as common tests for identifying BLV-positive cattle. ELISA is widely used because it is practical and reliable for screening adult cattle.

If your cow is young and recently received colostrum from a BLV-positive dam, antibody testing can be harder to interpret. Merck notes that maternal antibodies can interfere with serology until about 4 to 6 months of age, so PCR may be more useful in calves. PCR detects proviral DNA in lymphocytes and can help clarify infection status.

A positive BLV test does not prove that a cow has lymphoma. To diagnose cancer, your vet may recommend CBC or hematology, fine-needle aspirate, biopsy, or necropsy with histopathology. Cytology can help, but Merck notes it may be difficult when samples are contaminated with blood. Because signs overlap with abscesses, tuberculosis-like disease, traumatic reticuloperitonitis, heart disease, and other cancers, a full workup matters.

Prevention focuses on stopping BLV from moving in blood cells from one cow to another. Merck and USDA APHIS both emphasize that there is no vaccine and no treatment that clears infection, so herd management is the main tool. Important steps include never reusing needles, cleaning and disinfecting equipment between animals, using bloodless or cautery dehorning methods when possible, and improving hygiene for procedures like ear tagging, tattooing, castration, and palpation.

Regular testing is also important. APHIS notes that ELISA, AGID, and PCR can identify infected cattle. In lower-prevalence herds, your vet may recommend testing and culling positives, then retesting in 30 to 60 days and continuing surveillance. Merck describes repeat testing every 6 months during eradication efforts, with careful screening of incoming animals before they join the herd.

Fly control, clean handling facilities, and thoughtful colostrum and calf-feeding plans may also help reduce risk. For replacement animals, ask your vet about pre-purchase testing and quarantine protocols. Prevention works best when it is consistent, herd-wide, and tailored to your operation rather than handled one cow at a time.