Dr. Ray Sweeney presented this material for DAIReXNET on October 14, 2015. To view the full presentation, please see our archived webinars page at http://www.extension.org/pages/15830/archived-dairy-cattle-webinars

1. DAIReXNET is proud to present today’s webinar:
Bovine Leukosis Virus: What is it and What
Does it Mean for Me?
Dr. Ray Sweeney, University of Pennsylvania
During this presentation. Dr. Ray Sweeney will discuss some of the big questions you may have about
bovine leukosis virus. If you've been wondering about BLV, here’s where you learn all about it! The
questions Dr. Sweeney will cover are:
What is BLV?
How is it spread?
What happens when cows are infected with BLV?
How is an infection diagnosed?
Is there a treatment?
How do we prevent infection?
Today’s session will be recorded and archived at
http://www.eXtension.org/pages/Archived_Dairy_Cattle_Webinars

2. Our Next Webinar:
The Importance of Animal Handling for Dairy
Cattle
Dr. Kathryn Proudfoot, The Ohio State University
November 5th, 2015
12:00 PM Central
In this webinar, Dr. Proudfoot will discuss why using appropriate animal handling practices is so
important for dairies! She will touch on cow memory and how that can influence fear responses
to handlers.

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4. Bovine Leukosis Virus:
What is it and What Does it Mean for Me?
Raymond W. Sweeney, VMD
University of Pennsylvania School of
Veterinary Medicine
New Bolton Center

5. Outline
• What is BLV?
• How do cows get BLV?
• Who has BLV?
• What happens to cows with BLV?
– Disease?
– Production?
• What can I do to control BLV?

6. What is BLV?
• Retrovirus
– Bovine Leukosis
Virus
– “Bovine Leukemia
Virus”
– Enzootic Bovine
Lymphosarcoma
http://www.altmetric.com

7. What is BLV?
• Related to:
– Avian Leukosis virus
– Feline Leukemia virus
– Human T-cell
lymphotrophic virus
• Distant cousin to:
– Caprine arthritis
encephalitis virus
– Human Immunodeficiency
Virus
http://www.altmetric.com/

8. Bovine Leukosis Virus
• Conventional Wisdom: BLV does NOT infect
people!!

9. Bovine Leukosis Virus
• New Research:
??

10. BLV-Human Risk?
• BLV virus has been found in human mammary
tissue
• More frequently found in samples from breast
cancer than non-cancerous control samples
PLOS-One, September 2, 2015

11. Retrovirus Facts
• Infection is for Life!
– Virus is always present in white blood cells

12. Retrovirus Facts
• Long incubation period
– Many infected individuals never become diseased

13. Outline
• What is BLV?
• How do cows get BLV?
• Who has BLV?
• What happens to cows with BLV?
– Disease?
– Production?
• What can I do to control BLV?

14. BLV Transmission
• BLV is transmitted by White Blood Cells, which
carry the virus

15. Blood Transmission
• Flies

16. Blood Transmission
• Surgery, dehorning, needles

17. Blood Transmission
• Rectal examination (pregnancy diagnosis)

18. Blood Cell Transmission-Other
• Colostrum or milk
• In-utero
• Direct contact
• Semen

19. Outline
• What is BLV?
• How do cows get BLV?
• Who has BLV?
• What happens to cows with BLV?
– Disease?
– Production?
• What can I do to control BLV?

20. How Can We Tell Who Has BLV?
• Antibodies in serum or milk are a reliable test
for infection
– Serum AGID or ELISA
– Milk ELISA through DHIA
– Bulk milk can be tested
– EXCEPTION! Uninfected calves may still have
antibody from colostrum up to 6 months of age

23. Outline
• What is BLV?
• How do cows get BLV?
• Who has BLV?
• What happens to cows with BLV?
– Disease?
– Production?
• What can I do to control BLV?

24. BLV Infection
• Cattle develop antibodies in blood within 6
weeks of infection.
• Remain positive for life (AGID or ELISA)
• The majority of cows with BLV infection NEVER
GET SICK!
• 2%-3% of cows develop cancer
(lymphosarcoma), usually after 2-4 years
• There is no practical treatment for BLV

25. Economic Impact
• Death/culling due to cancer (lymphosarcoma)
– 2%-3% of infected cows
Abomasum
Heart

26. Lymphosarcoma
Spinal Cord
Eye
Uterus

27. What about outwardly healthy BLV
cows?
• Do BLV+ cows produce less milk?
– Multiple studies with conflicting results
– Many studies show no difference
– Other studies show about 2% - 3% reduction in
herd milk production
--Annual Value of
Production in BLV+ herds
was reduced $59/cow– (Ott et
al, 2003)

28. What about outwardly healthy BLV
cows?
• Some studies show an effect on immune
function, which could cause:
– Reduced response to vaccines?
– Increased susceptibility to infections?
– Research continues on this subject
• Cull rates in BLV+ herds were higher in some
studies, no difference in others
• Conclusion: BLV might affect cow health in
cows even if they don’t develop cancer

29. BLV Economic Impact
• Export
– Most countries require BLV- status
– Screening springing heifers for export results in
10-20% refusal rate due to BLV+

30. Outline
• What is BLV?
• How do cows get BLV?
• Who has BLV?
• What happens to cows with BLV?
– Disease?
– Production?
• What can I do to control BLV?

31. BLV Control: Why Should I?
• Raise animals for export or stud
– Foreign markets closed to BLV+
• Reduce losses from cows developing
lymphosarcoma
– Milk production
– Carcass condemnation

32. BLV Control: Why Should I? (cont.)
• What if human link is verified, or
publicized?
– Mandatory control
– Public perception and effect on consumption of
dairy products?
• First step: Discuss testing (bulk milk,
individual cow milk or serum) for BLV to see
“how bad is it?”

33. BLV Control-Goals
• IF I Have a BLV-free herd and want to maintain
BLV-free status (rare in US!)
– Maintain closed herd
– Test all additions before admitting to premises

34. BLV Control Goals
If my herd has BLV
• Eradicate?
– Test/segregate/control strategy
• Not reasonable if high prevalence
• Live with it
– Do nothing
• OK if not having financial impact now, but…
• What if human link?
• Begin steps to reduce infection
– Delay/prevent infection in young stock to:
• Reduce prevalence and reduce cancer losses
• Raise BLV-negative heifers for sale
• Easier to eradicate in future if need

35. Control Steps
• Colostrum
– Antibodies in colostrum from infected cow are
protective to calf
– Treat colostrum to kill virus but preserve
antibodies
• Freeze solid
• Heat treat, 145oF for 30 minutes

36. Control Steps
• Maintain separation of calves from adults
• Individual hypodermic needle
• Disinfect dehorning and tattooing instruments
• Individual rectal sleeve

37. Conclusion
• BLV is widespread in US Dairies
• 3% of infected cows develop lymphosarcoma
• Simple management steps can reduce the rate
of infection
• Economic effect of BLV probably less than
other diseases, but…
• Take steps now to reduce prevalence in case
human link is confirmed

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