Veterinary Services 

Centers for Epidemiology and Animal Health October 2008 

_________________________________________________________________________________________________________________________ 

Bovine Leukosis Virus (BLV) 

on U.S. Dairy Operations, 

2007 

In 2007, the U.S. Department of Agriculture’s (USDA) 

National Animal Health Monitoring System (NAHMS) 

conducted the Dairy 2007 study. In all, 17 of the Nation’s 

major dairy States* participated in the study. These 

States divided into two regions and represented 79.5 

percent of U.S. dairy operations and 82.5 percent of U.S. 

dairy cows participated in the study. 

This information sheet presents and compares data 

on BLV prevalence in U.S. dairy cattle collected during 

Dairy 2007 and during a previous NAHMS dairy study, 

Dairy 1996. 

BLV 

BLV is a retrovirus that infects dairy and beef cattle’s 

lymphoid tissue, causing malignant lymphoma and 

lymphosarcoma in 1 to 5 percent of infected animals. 

The virus is transmitted to cattle primarily by direct 

exposure with infected blood, saliva, semen, and milk.1

Most BLV-infected cattle seldom present with clinical 

signs of disease. Signs of infection may include tumors 

in lymphoid tissues, enlarged lymph nodes, weight loss, 

decreased milk production, fever, loss of appetite, rearlimb weakness or paralysis, protruding eyeballs, 

gastrointestinal obstructions, and increased blood 

lymphocytes counts. Because no vaccine is available for 

BLV, virus specific antibodies found in serum or milk are 

a good indicator of exposure and a practical method for 

disease screening. 

Economic impact of BLV on U.S. dairies 

Producers can incur economic losses because of 

BLV through cattle deaths, reduced reproductive 

efficiency, increased replacement and veterinary costs, 

and the ineligibility to export live cattle, semen, and ova 

to countries where BLV control efforts are in place.2 3 

A BLV certification program conducted in New York 

indicated that the disease had a significant economic 

impact on operations with high seroprevalence of BLV in 

which morbidity and mortality rates were high due to 

malignant lymphoma. 

 

*States/Regions: 

• West: California, Idaho, New Mexico, Texas, and Washington 

• East: Indiana, Iowa, Kentucky, Michigan, Minnesota, Missouri, New 

York, Ohio, Pennsylvania, Vermont, Virginia, and Wisconsin 

The association between cattle exposed to BLV and 

herd-level productivity was studied using data from the 

NAHMS Dairy 1996 study.4

 This study found that herds 

with test-positive cows produced 218 kg less milk per 

cow, per year than those with no test-positive cows. 

BLV prevalence on U.S. dairies, 1996 and 

2007 

The Dairy 1996 study was the first statistically based 

study in the United States to provide a baseline 

prevalence of BLV and the measures for controlling it. 

During the study, blood samples from cattle on 1,006 

operations were tested using the Agar Gel Immunodiffusion test (AGID). Results showed that 89.0 percent 

of U.S. dairy operations had cattle seropositive for BLV; 

74.8 percent of these operations had an estimated 

within-herd prevalence of 25 percent or higher. Dairy 

operations with fewer than 100 cows had lower 

individual animal prevalences and were less likely to be 

seropositive for BLV than operations with more than 200 

cows. 

As part of the 2007 dairy study, bulk tank milk was 

collected from 534 operations with 30 or more dairy 

cows and tested with an Enzyme Linked-Immunosorbent 

Assay (ELISA) for the presence of antibodies against 

BLV. Results showed that 83.9 percent of U.S. dairy 

operations were positive for BLV (table 1). 

Table 1. Percentage of Operations in Which Bulk 

Tank Milk Tested Positive for BLV via ELISA, by 

Herd size 

Herd Size 

(Number of Cows) Percent Operations 

Small (fewer than 100) 83.2 

Medium (100-499) 82.1 

Large (500 or more) 100.0 

All operations 83.9 
BLV prevalence estimates were also reported by 

region: 78.4 percent of operations in the study’s West 

region and 84.4 percent in the East region tested 

positive for BLV antibodies. 

Only 7.5 percent of all operations had independently 

confirmed the presence of BLV on their premises via 

laboratory testing during the 12 months prior to the Dairy 

2007 interview (table 2). Of these operations, the 

majority (88.5 percent) submitted blood samples for 

disease confirmation. Only 6.3 percent submitted tissues 

for necropsy. 

Table 2. Percentage of Operations in Which BLV was 

Confirmed Via Laboratory Testing During the 

Previous 12 months, by Herd size 

Herd Size 

(Number of Cows) Percent Operations 

Small (fewer than 100) 5.7 

Medium (100-499) 12.4 

Large (500 or more) 7.8 

All operations 7.5 

Summary 

Although the 1996 and 2007 dairy studies used 

different testing methods (AGID vs. milk ELISA) and 

different samples (serum vs. bulk tank milk), both studies 

suggest that BLV is present on the majority of U.S. dairy 

operations. Different regions were used in the 1996 and 

2007 studies for the geographic distribution of dairy 

operations. For this reason, regional differences in BLV 

herd-level prevalence were not comparable. 

In addition, the Dairy 2007 study found that only 7.5 

percent of operations independently confirmed the 

presence of BLV on their operations via laboratory 

testing. Although no details were available regarding the 

reasons why these operations submitted samples for 

BLV testing, it is possible that they had cattle with clinical 

signs compatible with BLV. The low percentage of 

operations that tested for BLV supports the concept that 

although infection is common, clinical signs of BLV are 

not frequently observed. A lower percentage of small 

operations had antibodies detected than large 

operations. 

The high individual animal prevalence of BLV 

reported in the Dairy 1996 study suggests that testing 

and culling seropositive animals may not be a cost 

effective method to control the disease. Instead, 

preventing disease transmission by implementing 

preventive practices would likely be more cost-effective. 

Since the primary route of infection is through contact 

with infected blood, prevention involves eliminating blood 

transmission from cow to cow. Prevention practices 

include using a new needle for each injection, discarding 

or cleaning syringes contaminated with blood, and 

cleaning blood-contaminated equipment such as 

dehorning equipment and tattoo pliers. Additionally, 

feeding calves pasteurized colostrum and milk, and 

using BLV seronegative dams for embryo transfer 

should assist in reducing the incidence of BLV.1

To review complete reports from the Dairy 1996 and 

Dairy 2007 studies, visit the NAHMS Website at: 

http://nahms.aphis.usda.gov. 

References 

1. Hopkins SG, and DiGiacomo RF. Natural transmission of bovine 

leukemia virus in dairy and beef cattle. Vet Clin North Am Food Anim 

Pract. 1997 Mar;13(1):107-28 

2. Burny A, Bruck C, Chantrenne H, Cleuter Y, Dekegel D, Ghysdael J, 

Kettmann R, Leclerq M, Leunen J, Mammerickx M, Portetelle D. 1980 

Bovine leukemia virus: molecular biology and epidemiology. In: Klein, 

G. (Ed.), Viral Oncology. Raven Press, New York, pp. 231-305. 

3. Pelzer KD. Economics of bovine leukemia virus infection. Vet Clin N. 

Am Food Anim. Pract. 1997. 13 (1), 129-141. 

4. Ott SL, Johnson R, Wells SJ. Association between bovine-leukosis 

virus seroprevalence and herd-level productivity on US dairy farms. 

Prev Vet Med. 2003 Dec 12;61(4):249-62. 

_____________________________ 

For more information, contact: 

USDA–APHIS–VS–CEAH 

NRRC Building B, M.S. 2E7 

2150 Centre Avenue 

Fort Collins, CO 80526-8117 

970.494.7000 

E-mail: NAHMS@aphis.usda.gov 

http://nahms.aphis.usda.gov 

#N526.0708 

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