Risk Assessment for Bovine Leukosis Virus and Infection Control
If Bovine Leukosis Virus exists in the herd or if the herd is untested:
On Farm Biosecurity where Positive and Negative animals are co-mingled.
Feed newborn calves safe colostrum.
- Colostrum from recently tested negative fresh cows or banked negative colostrum donors.
- Powdered colostrum replacers.
- Frozen colostrum from positive or untested cows. There may still be a risk of transmission, especially if the donor cow is PL (persistently leukocytotic).
- Dehorn only with burning-type dehorners or with scrupulously disinfected* cutting tools. When doing bloody dehorning, keep calves separated until blood dries.
- Scrupulously disinfect* all equipment which may be blood contaminated: tattoo pliers, ear taggers, ear notchers (commonly used for BVD skin test in calves), hoof equipment, rectal ultrasound equipment, obstetrical equipment, tail docking equipment, tools used for extra teat removal
- Do not reuse any needles, IV hoses, OB sleeves, syringes containing any blood contamination, or any medicine vials that may be blood contaminated (OXYTOCIN)
- Control biting and sucking insects as much as possible.
- In a low-incidence herd, remove positive animals from the herd.
- Possibly test and remove BLV positive cows that are persistently leucocytotic (PL).
- There is no vaccination program for the control of BLV.
- Natural breeding can theoretically transmit virus from an infected bull with blood or lymphocytes in his semen, or from cow to cow, with the bull acting as a fomite. Artificial insemination with frozen semen and embryo transfer, even of unfrozen, properly handled embryos, are safe procedures if technicians observe above control measures.
- Milking transmission of infected somatic cells. This is a theoretical risk, but it has not been demonstrated to be very likely. Milking machines have been demonstrated to cause “jetting” of milk droplets toward and into teat orifices during machine squawking and claw vacuum fluctuations.
- Need to handle calves born to positive dams as if they are positive.
- Removal of PL cows may reduce this risk dramatically.
Physically segregating positive from negative individuals.
- Difficult to accomplish.
- Requires frequent testing of negative group, especially if rigorous on farm biosecurity measures, as outlined above, are not followed with negative animals.
- Allows positive group to be handled with less rigor.
If herd is test negative:
Prevent introduction of positive herd additions. Test all additions and retest in 60 days and possibly again in 6 months. Handle herd additions as if they are positive.
This virus is infectious when it is inside leukocytes. Transmission from off farm sources is unlikely except on equipment to be used on cattle that was recently contaminated with fresh blood or body fluids.
- Require all equipment brought onto the farm to be adequately disinfected.
- Provide fresh solutions of disinfectant to personnel who may not have their own, such as hoof trimmers, and require them to disinfect their equipment prior to using it.
- Do not share equipment at expositions or fairs.
- Consider all animals positive if they leave the farm and go to facilities where BLV management procedures are not followed. This may include heifer raisers, show strings, and reproductive facilities.
- Flies, especially tabanids (horseflies, deerflies) have been implicated in bringing BLV infection from off-farm infected cattle. This in considered a low risk, but one that should be managed, especially in BLV free herds.
*A very effective and readily available disinfectant for on-farm use is a solution of Clorox and water mixed at 1 part Clorox to 9 parts water (this is the equivalent of 1 quart Clorox to 2 gallons plus 1 quart water). This will kill the BLV virus, the lymphocytes containing the virus, and is effective against most other organisms including BVD virus, unless it is contaminated with organic matter. Replace if it gets manure, feed or bedding contamination. Most detergents will actually destroy the leukocytes, and effectively remove organic material prior to disinfecting.