“These herds with PI animals may have only a few of them, but they can cause a lot of grief.”
Going into its fourth year, the Montana BVD-PI Herd Biosecurity Project has enabled Montana beef producers to screen nearly 200,000 head of cattle. The goal is to provide education and technical assistance to producers who want to identify and eliminate animals persistently infected (PI) with bovine viral diarrhea virus (BVD) from their herds.
The program is an initiative of the Montana Stockgrowers Association and Montana State University, which administers the program through Clint Peck, director of Beef Quality Assurance, Mo Harbac, manager of Montana Beef Network, and John Paterson, beef cattle extension specialist. Participation in the program is totally voluntary.
“We thought we might get 20 herds and 10,000 head that first year, but we ended up with 50 herds and 40,000 head,” says Peck. The following year they tested 100,000 but numbers dropped back to about 50,000 head in 2008 when funding cutbacks did away with the cost-sharing arrangement. Judging from the calls coming in as calving season was getting underway, he expects to see participation ramp up again in 2009.
He feels this is largely due to the fact that a new pooled testing method has made it affordable for producers and because the project itself has helped to raise producers’ awareness about BVD.
“What’s sifted out of the project are the three legs of biosecurity,” Peck explains. “First is surveillance testing; second is proper and effective vaccination; and third is movement and handing practices.”
The primary source of BVD virus in beef herds is PI cattle. Dr. Bob Larson of the University of Missouri estimates even one PI animal in a herd will result in a loss of $15 to $25 per cow per year. This is due to a loss of reproductive efficiency and because BVD virus suppresses the immune system in susceptible animals, which inhibits their ability to fight off other infections.
BVD virus spreads in two ways.
Transient BVD infections spread from animal to animal when infected animals shed the virus and susceptible animals pick it up through the mouth or respiratory tract. Susceptible animals are those that haven’t been properly vaccinated or are already PI. The symptoms of an acute infection in susceptible, but otherwise healthy, non-PI mature animals are usually mild and may even go unnoticed. Young non-PI animals may become ill, but they generally recover unless there are complications when other diseases get a foothold. PI animals are unable to mount an immune response, even if they have been vaccinated, and will develop the fatal mucosal form of BVD if they contract the virus.
PI calves shed the virus throughout their lifetime. They occur when a susceptible dam contracts a transient BVD infection during pregnancy. The BVD virus transfers to the fetus via the bloodstream. Depending upon the stage of gestation at the time of the infection, the cow may abort or go on to deliver a deformed, weak or normal-looking PI calf, or a healthy non-PI calf.
“Odds are slim that a PI heifer will live long enough to become a breeding animal. If she does, every one of her calves will be a PI calf,” Peck explains. So far, the Montana screening project has identified one PI first-calf heifer and two PI cows — one being five years old.
Overall, one herd in every 12 to 13 has identified PI calves, which translates into about 0.1 per cent of all births. These calves perpetuate the disease cycle in their home herds and spread the virus wherever they are commingled with other cattle at community pastures, auction markets, feedlots and sale to other herds.
“So, we don’t need to be testing cows with calves. In the screening program, we test the calf or the aborted fetus because it could be PI, even if the cow isn’t,” Peck explains. The only time you need to test a mature animal is if the test on the calf or fetus comes back PI, or if you
buy in bred replacement heifers or first-calf heifer pairs with unknown BVD status.
For more information on the Montana BVD-PI Herd Biosecurity Project visit www.mtbqa.org.
“It’s estimated that nearly 10 per cent of herds in Western Canada have a PI animal,” says Dr. Andy Acton of Deep South Animal Clinic at Ogema, Sask. “These herds with PI animals may have only a few of them, but they can cause a lot of grief.”
Labs in Canada can test for BVD at an affordable cost and more producers have been testing for BVD because of this. Some thought has been given to the possibility of implementing general screening programs, however, the time just hasn’t been right with all of the trade issues Canadian producers have been dealing with for the past six years.
Acton feels a good place to begin would be for the major stock shows to require mandatory BVD testing for all cattle entering the grounds, such as some U. S. shows are already doing. Testing all breeding stock offered for sale is another priority area.
“It’s important to understand that there are different tests available. A pooled screening test such as Montana is using for surveillance purposes could very well miss positive animals and should not be used as a guarantee that a herd is free from BVD,” Acton explains. “True individual tests are the only tests acceptable for animals that will be transferred between herds.”
If you think you might have a BVD problem in your herd, talk with your veterinarian about what you want to achieve, the appropriate testing method and interpretation of the results.
Should You Be Worried About Bvd?
Answer yes or no to each question
1. Do you vaccinate your new calves for BVD virus to prevent disease using a protocol recommended by your veterinarian?
2. Do you vaccinate your heifers and cows for BVD to prevent reproductive losses using a protocol recommended by your veterinarian?
3. Was last year’s herd pregnancy rate (number diagnosed as pregnant divided by number exposed) greater than 90 per cent?
4. Did greater than 95 per cent of your cows calve within a 90-day window?
5. Has your calving rate (number that deliver a live calf divided by number diagnosed as pregnant) been above 90 per cent in the past three years?
6. Do you regularly have tissue from aborted fetuses tested for BVD virus or submit them to your veterinarian for a post-mortem examination?
7. Do you isolate all new additions to your herd for at least 21 days before turning them out with their counterparts?
8. Did you treat less than 10 per cent of last year’s calf crop for respiratory or digestive disease while you owned them?
9. Were your pregnant cows and heifers kept from commingling during the first part of the breeding season with cattle from herds of unknown health status?
10. Were you able to keep your pregnant cows or heifers from having fence line contact with cattle herds not tested for BVD virus during the early part of the breeding season?
11. Do you test purchased replacement cattle and seedstock for BVD virus before breeding season (preferably at least 30 days prior)?
12. Do you make sure all purchased bred heifers are tested for BVD virus and do you (or will you) test their calves for BVD virus before commingling the heifers and their calves with your home herd?
13. Do you have a biosecurity protocol for “re-receiving” cattle following off-farm trips for heifer or bull development, lending or leasing, cattle shows, county fairs, vet clinics?
14. Do you have a general sanitation program on your ranch, including regular cleaning of trailers, working facilities, watering devices and hospital areas and do you enforce a sanitation protocol for people, equipment and vehicles entering your operation that have recently visited other cattle operations?
15. Do you have a thorough understanding of the routes of BVD virus transmission, the nature of BVD virus infection ( transient vs. persistent) and the stage of pregnancy associated with the creation of BVD-PI cattle?
# “Yes” / 15 x 100 = ______%.
100-80% = Low Risk — Set as a goal to answer 100 per cent “yes” to the above questions. In consultation with a veterinarian re-evaluate BVD virus biosecurity each year well in advance of the breeding season.
60-80% = Moderate Risk — Consult with a veterinarian for assistance. At least 30 days before the start of the breeding season conduct a partial-herd BVD virus test. Consider a whole-herd test. Set as a goal to answer 100 per cent “yes”.
0-60% = High Risk — Consult with a veterinarian for assistance. Set as a goal to answer 100 per cent “yes” to the above, and, at least 30 days before the start of the breeding season conduct a whole-herd test.