Extension Responds: BSE
Facts about Bovine Spongiform Encephalopathy (BSE)
By: Larry Baumann, Extension Veterinarian, University of Wisconsin – River Falls/Extension
What is BSE?
A. BSE is a slow progressive disease of cattle that affects their nervous system. The acronym, BSE, stands for Bovine Spongiform Encephalopathy. It is also called “mad-cow disease” although that's not a very accurate description of the disease. The preference is to refer to this disease as BSE.
What causes BSE?
A. BSE is caused by prions. These are abnormal proteins and are quite different from bacteria and viruses.
Why are we concerned about BSE?
A. There is evidence that BSE may cause a disease in humans called variant Creutzfeldt-Jakob Disease (vCJD) This disease is a fatal, degenerative neurological disease in humans. Prions are also a concern because they are very hard to destroy. They do not evoke an inflammatory response or an immune response in the body and normal sterilization methods have no effect on them.
A. Where did BSE come from?
BSE was first reported in the United Kingdom in 1986. It has been reported in many European countries and was reported in Canada on May 20, 2003. BSE was reported in the United States on Dec. 23, 2003, in a Holstein dairy cow from a Washington state dairy farm. This cow was imported from Canada in 2001.
How is BSE spread?
A. BSE is spread by ingestion of the BSE prions. The prions are found in an infected animal's nervous tissue, so ingestion of any nervous tissue products may contribute to the spread of BSE. It does not spread by direct contact, air, manure, urine, semen or milk. The infective dose for BSE is very small, less than a gram of contaminated nervous tissue. Investigators believe that the infected cow in Washington consumed contaminated feed as a calf and became infected with BSE. The incubation period, which is the time from first becoming infected with a pathogen until clinical signs of the disease appear, for BSE is four to six years, but the disease may be detectable by microscope as early as 20 to 30 months after ingestion.
What are the clinical signs of BSE?
A. Clinical signs of BSE in cattle include behavior changes, nervousness, abnormal posture, loss of coordination, trembling and decreased milk production.
How can cattle be tested for BSE?
A. Currently no test is available to detect BSE in live animals. The current method for diagnosing BSE is to examine brain tissue under a microscope after death of the animal.
How many cattle are at risk of BSE in the U.S.?
A. All cattle are considered to be at risk of BSE. There are approximately 104 million cattle in the United States. Most (80 million) are beef breeds and the remaining 24 million are dairy breeds. Approximately 88 million are classified as beef/feedlot cattle and the remaining 16 million are classified as dairy cattle. Estimated numbers by beef or dairy breeds are given in the table below.
US Cattle Inventory as of August 5, 2003 (numbers x 1000 & % total)
Cattle Type |
Beef Breeds |
Dairy Breeds |
Total |
|---|---|---|---|
# Cows |
33,600 (32%) |
9,100 (9%) |
42,700 (41%) |
# Heifers (>500#) Replacements |
4,600 (4%) |
3,600 (3%) |
8,200 (8%) |
# Heifers (>500#) Other (feedlot) |
7,100* (7%) |
600* (.6%) |
7,700 (7%) |
# Steers (>500#) Feedlot |
10,000* (10%) |
4,200* (4%) |
14,200 (14%) |
# Bulls (>500#) |
2,050* (2%) |
50* (.05%) |
2,100 (2%) |
Calves (<500#) |
22,500* (22%) |
6,500* (6%) |
29,000 (28%) |
Total # Cattle |
79,850 (77%) |
24,050 (23%) |
103,900 (100%) |
* estimated
How many cattle are slaughtered annually in the U.S.?
A. Approximately 35 million. Most (27 million) are beef breeds and the remaining 8 million are dairy breeds. Approximately 29 million head are classified as fed cattle and the remaining 6 million are classified as cull breeding cattle. The estimated numbers of slaughter cattle by beef or dairy breeds are given in the table below.
Estimated number of slaughtered cattle in the US as of December 2003
(number x 1000 & % total)
Cattle Type |
Beef Breeds |
Dairy Breeds |
Total |
|---|---|---|---|
# Cows |
3,100 (9%) |
2,600 (7%) |
5,700 (16%) |
# Heifers |
10,500* (30%) |
800* (2%) |
11,300 (32%) |
# Steers |
13,000* (37%) |
4,500* (13%) |
17,500 (50%) |
# Bulls |
580* (2%) |
20* (.05%) |
600 (2%) |
Total # Cattle |
27,180 (77.5%) |
7,920 (22.5%) |
35,100 (100%) |
* estimated
How many “Downers” are slaughtered annually in the U.S.?
A. Before U.S. Department of Agriculture banned the practice on Dec. 30, 2003, about 150,000 downer cattle were slaughtered each year.
What measures are being taken to control and prevent the spread of BSE?
A. The USDA has taken several measures to prevent the spread of BSE.
1) banning and restricting imports of cattle and cattle products;
2) banning risky feed ingredients; and
3) testing and surveillance of cattle in the US.
Cattle and cattle products imports are banned from all European countries, Japan, Israel, Canada and other counties where BSE has been reported. In 1997, the USDA banned ruminant proteins and feed products from use in ruminant rations. Surveillance has involved testing more than 48,000 cattle brains during the past several years. All the cattle tested were free of BSE have until Dec. 23, 2003, when the first U.S. case was discovered.
What will happen in the future?
A. USDA has already implemented several changes since Dec. 23. These include the ban on non-ambulatory and disabled (downer) cows from the human food supply. More changes are likely in the near future. The USDA will continue to do BSE surveillance. A separate program for reporting, collecting and testing samples may be initiated. One source of current and future changes related to BSE is the USDA website at www.usda.gov .
For more information: Larry Baumann, Extension Veterinarian, University of Wisconsin – River Falls/Extension, (715)425-3187, larry.baumann@uwrf.edu