Agriculture : News
DATE: July 11, 2010
HARDIN COUNTY COOPERATIVE EXTENSION SERVICE
201 Peterson Drive
Elizabethtown, Kentucky 42701-9370
BY: Doug Shepherd
County Extension Agent for Agriculture and Natural Resources
Bovine Viral Diarrhea Virus: Is My Herd at Risk?
BVD (Bovine Viral Diarrhea) disease is one of the most complicated viral diseases in beef and dairy cattle worldwide. Terms associated with BVD such as “cytopathic” vs. “noncytopathic”, “persistent infection” vs. “transient infection”, “types I and II” and “immunosuppression” make understanding this virus a difficult task. However, the results of this disease are very clear: economic losses due to poor performance, loss of milk production, open cows, abortions, calf sickness and death. In order to control this problem, producers must first know if the virus is circulating in their herd. If so, then efforts must be focused on finding those infected individuals, minimizing their harmful effects and eliminating them from the herd at the right time. If the herd is free of BVD virus, then it is of the utmost importance to keep the virus out and minimize losses if it is accidentally introduced.
The following information was supplied by Dr. Michelle Bilderback, UK Extension Veterinarian, and provides a good basis for all producers to use in determining the potential of this disease in their herd. First, a basic understanding of the disease is essential to finding the appropriate strategy for your farm. The virus is picked up by a cow or calf by breathing it in (inhalation) or swallowing (ingesting) the organism. The virus can survive in the environment up to 7 days and may be brought in on trucks, tractors, boots, gloves or carried in by wild animals. It can also travel in the air, including across fences from a neighboring farm. However the most important source of the virus is a cow or calf already infected with BVD. Once exposed, what happens next depends on the immune system of the cow or calf (vaccination status), aggressiveness (“virulence”) of that strain of virus, and the overall stress level present in the herd. Symptoms of disease range from a mild fever to severe diarrhea and death.
Clinical signs of acute BVD (also known as “Transient” or “Primary” BVD) disease in calves 3-12 months old may include: (1) Fever, (2) Diarrhea, )3( Unthrifty/Rough hair coat (calf looks “wormy”), (4) Coughing, (5) Lameness, (6) Ulcers in the mouth (slobbering), (7) Hemorrhage (bleeding) and, (8) death. Perhaps the most important symptom of BVD virus in calves is one we cannot see - “immunosuppression”. The virus actually keeps the calf’s immune system from functioning properly so other infectious diseases such as pneumonia and calf scours are much more severe and often lead to death.
Clinical signs in cows are generally mild and seldom noticed but the infection causes serious consequences if it occurs during breeding season or early pregnancy (1st and 2nd trimesters). Reproductive effects of the BVD virus include: (1) Failure to Conceive, (2) Early Embryonic Loss (Long time to return to heat), (3) Abortion (up to 6 months), (4) Mummified Fetuses, (5) Developmental Defects or “Dummy Calves”, and/or (6) Calves with eye defects such as cataracts and retinal degeneration.
The most important consequence occurs if the cow is infected with the BVD virus between 42-125 days of gestation. In this short window of time, the unborn calf contracts the virus and is never able to get rid of it for the rest of its life. When this calf is born, it is “persistently infected” or a “PI” calf. If infection occurs from 180 days on, a normal calf is produced.
The “PI” animals are the reason BVD disease continues. They are the primary source of virus transmission because they shed an extremely high number of virus particles throughout their lives. A PI animal is a virus factory, daily producing millions of virus particles in all body secretions including feces, urine, saliva, nasal discharge, milk, semen, uterine secretions, and aborted membranes. These contaminated body fluids are deposited on the grass, in ponds, watering troughs, feed troughs-virtually everywhere the animal goes, thus easily enabling the spread the disease to other animals in the herd.
Although it is often assumed that PI calves are stunted, will grow poorly and usually die young, some are absolutely normal and will survive well into adulthood and have calves. Unfortunately, if a PI female gets pregnant, her offspring will be a PI calf 100% of the time. This is important because if one PI calf is out in the pasture constantly shedding virus during breeding season, many (if not all) of the cows will be exposed during the highest risk time.
Getting your herd tested is fairly easy and inexpensive. With a little training, you can do the testing yourself or your veterinarian can collect the samples for you. Central States Testing Lab located on Mulberry Street in Elizabethtown can conduct the BVD-PI tests for you or samples can be submitted to the UK Livestock Diagnostic Lab in Lexington. Contact your veterinarian about whether or not to test your herd and/or for more information on this disease. Information is also available at the Hardin County Cooperative Extension Service Office about BVD and BVD-PI testing.
Even though the percentage of BVD-PI calves nationwide is extremely low, one BVD-PI calf in a herd or feedlot pen, can really cause havoc to all the other animals that infected animal is housed with. Thus, identification of possible BVD carriers in a herd should be an important management strategy.
Welcome Matt:
Matt Adams recently accepted and was hired to the position of Hardin County Agriculture Extension Program Assistant, and is now working out of the County Extension Office. Matt lives in Upton, recently graduated with an Ag degree from Western KY University, has a beef herd and has developed a commercial hay operation. He’s the son of Ken and Jane Adams of Upton.
Matt will be working with all aspects of the County Cooperative Extension Agriculture program right along with the Ag Agents. We’re glad to have him on board and look forward to all he can provide to the agricultural community in the future. Stop by and introduce yourself to our newest Extension staff member!
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