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October 2021

Latest Bovine Leukosis Virus (BLV) Management Recommendation

By Dr. Gregg A. Hanzlicek

It is estimated that only about 5% of the bovines infected with bovine leukosis virus will become clinical. A retrospective evaluation of eight million slaughter records revealed that clinical BVL was the number one reason dairy cow carcasses and the number two reason beef cow carcasses were condemned at slaughter facilities.1 In addition, several studies have linked BLV positivity to lower production and earlier culling in dairy herds.2-4 The effects on production and health in beef herds is assumed to be similar but has not been studied to the author’s knowledge.

The KSVDL receives a lot of samples for BLV testing. Most of the herds have at least one positive animal; the within herd prevalence many times approaches 60%-100%. Anecdotal reports in other areas of the U.S. report that both between and within herd prevalence rates are increasing.

Given that many herds have moderate to high prevalence levels, testing and culling is not a practical control option. Several recent studies have indicated that the proviral bovine leukemia load of animals is a good predictor of transmission risk.5,6 Animals with high proviral loads are at a high risk of transmitting the virus to herd mates, whereas animals with low proviral loads are a low risk of transmission. Several studies have reported that herds which identify and cull only those animals with the highest viral load can significantly reduce the spread of this virus within the herd.5,6

KSVDL’s Bovine Leukemia Virus (BLV) PCR (MDL-3370) can be used to estimate the proviral load of animals within the herd. The cycle time (Ct) value provided with each PCR BLV test result can identify those high transmission risk animals. This relatively new technology allows veterinarians and producers to identify the highest virus carrying animals and either cull or segregate them during the vector season as another control method.

Below is a table with the Ct and estimated virus load per 1 ml. of whole blood

Proviral Load

Ct

average concentration/ml blood

Ct

average concentration/ml blood

1

103,079,215,104,000

19

393,216,000

2

51,539,607,552,000

20

196,608,000

3

25,769,803,776,000

21

98,304,000

4

12,884,901,888,000

22

49,152,000

5

6,442,450,944,000

23

24,576,000

6

3,221,225,472,000

24

12,288,000

7

1,610,612,736,000

25

6,144,000

8

805,306,368,000

26

3,072,000

9

402,653,184,000

27

1,536,000

10

201,326,592,000

28

768,000

11

100,663,296,000

29

384,000

12

50,331,648,000

30

192,000

13

25,165,824,000

31

96,000

14

12,582,912,000

32

48,000

15

6,291,456,000

33

24,000

16

3,145,728,000

34

12,000

17

1,572,864,000

35

6,000

18

786,432,000

36

3,000

Data provided by Dr. Jianfa Bai, KSVDL Molecular R&D Section Head.

References:

  1. White, T.L.; Moore, D.A. Reasons for whole carcass condemnations of cattle in the United States and
    implications for producer education and veterinary intervention. J. Am. Veter. Med. Assoc. 2009, 235, 937–941.
  2. Norby, B.; Bartlett, P.C.; Byrem, T.M.; Erskine, R.J. E_ect of infection with bovine leukemia virus on milk
    production in Michigan dairy cows. J. Dairy Sci. 2016, 99, 2043–2052.
  3. Ott, S.L.; Johnson, R.;Wells, S.J. Association between bovine-leukosis virus seroprevalence and herd-level
    productivity on US dairy farms. Prev. Veter. Med. 2003, 61, 249–262.
  4. Erskine, R.J.; Bartlett, P.C.; Byrem, T.M.; Render, C.L.; Febvay, C.; Houseman, J.T. Association between bovine
    leukemia virus, production, and population age in Michigan dairy herds. J. Dairy Sci. 2012, 95, 727–734.
  5. Ruggiero, V.; Norby, B.; Benitez, O.; Hutchinson, H.; Sporer, K.; Droscha, C.; Swenson, C.; Bartlett, P.
    Controlling bovine leukemia virus in dairy herds by identifying and removing cows with the highest proviral
    load and lymphocyte counts. J. Dairy Sci. 2019, 102, 9165–9175.
  6. Taxis, T.M.; Sporer, K.R.B.; Droscha, C.J.; Niles, D.; DeJong, T.; Swenson, C.L.; Bartlett, P.C. Reducing bovine
    leukemia virus prevalence on a large midwestern dairy farm by using lymphocyte counts, ELISA antibody
    testing, and proviral load. Bov. Pract. 2020.

 

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