The Hidden Cost of Bovine Leukemia Virus on Dairy Cows
January 4, 2017
Paul C. Bartlett, Phil Durst, Howard Straub, Brook Wilke, Bo Norby, Rebecca LaDronka and Vickie Ruggiero
A recent national survey showed that 47% of dairy cattle have been infected with bovine leukemia virus (BLV). Most dairy producers know about the losses due to the occasional lymphoma, but do not appreciate the subclinical losses associated with the immune disruption leading to lost milk production and decreased cow longevity30. When asked “How much of a problem do you believe BLV is for your herd?”, 50% of dairy producers in our national study of 103 herds thought that BLV was not a problem at all. An additional almost 40% thought that BLV was a small problem, but not significant, leaving only slightly more than 10% who thought that BLV was a significant problem.
Lack of precise information regarding the costs of reduced milk production and cow longevity has discouraged researchers from making rough estimate of the total cost of BLV infection. However, a rough estimate may be better than no estimate at all, and lack of an estimate does not mean that the estimate is $0.
The W.K. Kellogg Biologic Station Pasture Dairy Center recently undertook an aggressive new plan to reduce its prevalence of BLV. At the start of the program in 2015, we estimated how much BLV was costing this farm. Our summation of the various cost components was computed in a spreadsheet, which you can download here. We can’t tell you the exact cost of BLV to your farm, but perhaps you can use our approach to give yourself a rough estimate.
Bovine leukemia virus is an infection that causes bovine leukosis (enzootic bovine leukosis). Until relatively recently, the only known cost associated with this disease was from the tumors (lymphoma) that develop in less than 5% of infected cows56. This was not a big concern in the 1970’s when less than 10% of our nation’s dairy cattle were infected with BLV and when other national disease control programs were prioritized. However, many nations started BLV eradication programs, and now at least 21 have eliminated BLV from all their dairy and beef cattle. See the BLV Prevalence section for more information.
Infection with BLV disrupts a cow’s immune system3,56. Without a fully functioning immune system, infected cattle are susceptible to a wide array of opportunistic pathogens similar to what occurs in humans with HIV/AIDS (a close retrovirus cousin). Cows culled for a wide variety of reasons (poor production, mastitis, lameness, etc.) may have been more severely affected by these problems because their immune systems were not fully functional6. Also, the immune dysfunction is likely responsible for the decreased milk production seen in older dairy cattle5,8.
The Spreadsheet Partial Budget:
Economists call it a “Partial Budget” when you estimate total economic impact by adding up various cost components. Our spreadsheet is available here. You can download our Excel© spreadsheet for the KBS Pasture Dairy Center, and can edit the input values as appropriate for a different herd.
Table 1: The input values shown are for the KBS Pasture Dairy Center in 2015.
The inputs needed are shown in light blue. You can substitute your own numbers into the blue parts of the spreadsheet which will re-calculate to show (in the yellow boxes) a rough estimate of how much money BLV could be costing you each year.
Table 2: The output values shown are for the KBS Pasture Dairy Center in 2015.
The USDA 1996 dairy study determined that 25.322 (115 kg) of milk (per cow/year) was lost for each 10 percent increase in BLV-infected cows within a herd32. Our recent Michigan study found nearly identical herd-level production losses as did this NAHMS study5. We estimated that 25.322 lbs (11.5 kg) of rolling herd average milk was lost for every 1% increase in BLV herd prevalence (Figure 1).
Cost of Tumors:
BLV-associated tumors are now the most common reason that USDA condemns cattle10. Depending on the terms of the sale, the producer may or may not lose the full slaughter value of the animal if it is condemned at slaughter.
The estimate of reduced survival of ELISA-positive cows as compared with their negative herdmates (Figure 2) was based on a 2010-2012 study of 3,849 cows in 112 Michigan herds in which cows were followed for an average of 597 days6. BLV-positive cows were 23% more likely to be culled than were BLV-negative cows. We attempted to estimate the economic loss when an average milking cow turns into an average cull cow. The average sale price for a cull cow can usually be recalled by most producers. Estimating the value of the average milking animal is more difficult since there is generally not a big market for such animals. The best approach may be to think of the lowest price you would accept to sell an average milking-aged cow from your herd.
You can include in your analysis any additional costs for BLV testing, single-use needles and sleeves, loss of export markets, colostrum handling, fly control, isolation pens for BLV-positives or any other extra costs incurred to prevent or control BLV56.
Association and causality: The confounding effects of other factors and intermediate causes can be responsible for some or all of the associations we observed between BLV and milk production and between BLV and reduced cow longevity (survival in the herd). Therefore, these measures of BLV impact on production and cow longevity must be taken as rough estimates. A more complete discussion can be found in the “Explanation and Interpretation” tab of the spreadsheet. However, based on our recent national survey cited above, many producers think BLV has little if any impact30. In this case, a rough estimate may be better than no estimate at all. Absence of a cost estimate for BLV doesn’t mean that the best estimate is zero dollars. We therefore proposed a rough cost analysis for the KBS herd that you may be able to use as a guide to estimate the cost of BLV on your own herd.
Download the Spreadsheet (Excel): You can obtain a copy of the above referenced Excel spreadsheet here.
Where to start: If you are unaware of what your herd’s BLV prevalence, we recommend that you start with a BLV Herd Profile. The Herd Profile can be done as a milk ELISA test through your DHI organization and samples by submitting milk or serum from the 10 most recently fresh cows of each lactation (1st, 2nd, 3rd, and 4th+). The Herd Profile is highly correlated with the prevalence found with whole herd testing, and at a much lower cost.
Conclusion: BLV has been slowly increasing in U.S. cattle, and is starting to get some attention. As the spreadsheet analysis shows, the cost of BLV can be greater than is commonly realized. Now may be the time to start controlling this disease.