CONVERSATIONS: Total BVD management
Vaccination and treatment are common methods of controlling herd health problems, but conversations with your veterinarian should also seek to identify subclinical cases and uncover the underlying causes.
By Dr. Bruce Hoffman, DVM
“I really would rather not know.”
That’s the answer I hear over and over again in my conversations with dairy operators when asked if they have a suspected disease in their herd. Perceptions of health-related issues are focused on what is visually seen and, unfortunately, this visual reliance is accurate with the major problems, but not underlying issues robbing cows of needed efficiencies.
There is also an overriding confidence in vaccinations for the prevention and control of the major pathogens we regularly fight. Lost, or stressed less frequently, is the need to exclude or reduce the bugs that negatively affect production and the bottom line from the start.
Why should you care? Because it’s costing you money and limiting your cows’ abilities to “be all they can be” for making milk. Dairy producers no longer need to say “I don’t think I have a problem” or “I can’t afford to know.” We have the tools to make it simple and cost-effective. We just need to use them.
1) Isn’t vaccinating enough?
Each of you has no doubt read a recent article or heard a talk on bovine viral diarrhea (BVD). The disease’s negative effects are worrisome, but you think you are covered. Your answer to a possible BVD issue is “I vaccinate for it, I’m in the clear.” My response is another question: What else are you doing to protect your herd from a virus that is costing between $20-$88 per cow a year. Never has it been so easy to look for BVD and monitor its presence in your herd.
Ask your veterinarian to review your herd’s current program for detecting and controlling BVD. Ask if testing is part of the protocols.
2) Is testing every animal in the herd necessary?
Prior to the use of reverse-transcriptase polymerase chain reaction (RT-PCR) diagnostics, the main method for identifying BVD in herds was to test every individual animal for the presence of persistent infection (PI). The RT-PCR testing method detects the actual virus in a bulk tank milk sample, and is sensitive enough to detect small amounts in diluted samples. If the virus is found, data confirms a PI is in the herd and shedding huge amounts of virus daily.
After the initial testing phase, take quarterly samples, since some cows are dry and are not represented in a milk sample. If they all are negative, and management practices remain the same, testing can be reduced to once or twice a year. If a positive is identified, string samples are done, and only the positive pen needs to be individually sampled. This procedure reduces the cost and workload dramatically to identify and remove the problem PI. With recent diagnostic advancements, PIs in the milking string (up to 3,500 cows) can be identified for as little as $250 per year.
Ask your veterinarian to discuss new testing technology and schedules.
3) Where does surveillance come into play?
Currently, surveillance is not routinely practiced with regard to BVD prevention or detection. The general view is that either every herd is afflicted, or they are all healthy. This rationale is based purely on visual observations of the cattle population. Unfortunately, without proper diagnostic testing, the BVD virus is not readily seen, since the afflicted cattle don’t show visible signs of illness. In other words, the disease is subclinical. Although the increased use of BVD vaccine has reduced the overall incidence of acute disease caused by BVD virus, it has not eliminated the formation of PIs which serve as the main reservoirs of virus survival. The ease of identifying the positive dairies makes surveillance a “no brainer.”
Ask your veterinarian to review the clinical incidence of BVD in your herd. Discuss the potential incidence and risk for subclinical cases.
4) How do changes in the dairy industry impact BVD infection?
With herd numbers decreasing, but growing in size, management changes are making it easier for stealthy PI to survive. When dairies expand, cows must come from somewhere, and very few operations are meeting expansion needs with their own heifers. Instead, springers are shipped around the country. Knowing the herd health history of the heifer source is important. According to the 2007 NAHMS survey, less than 20% of dairies take any measures – including quarantine, testing or vaccination – to prevent diseases from entering their herd. The same survey showed 12.8% of dairies >500 head were positive for BVD in the bulk tank.
If you’re expanding, ask your veterinarian about protocols to determine the health history and status of purchased animals.
5) How did BVD find us?
If a BVD PI is found in the milking string, review how it got there. Was it raised or purchased? Is the dairy using an offsite grower to raise and breed the heifers? Does the grower commingle heifers from multiple sources especially during breeding? What lactation was the animal? Which population is at risk due to virus shedding?
Answers can then be used to create a testing program to eliminate the formation of PIs that are causing underlying issues with reproduction, mastitis, respiratory disease and lower milk production. On higher-risk operations like calf ranches and expanding dairies, it’s important to test day-old heifers, removing PIs early before they can do harm.
• Dr. Bruce Hoffman, DVM, is president of Animal Profiling International, Inc., based in Portland, Ore. Contact him via phone: 406-282-7414; e-mail: firstname.lastname@example.org or visit www.animalprofiling.com.