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:
- 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. - 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. - 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. - 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. - 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. - 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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