Am writing this column shortly after the first case of Bovine Spongiform Encephalopathy (BSE) was confirmed in the United States. This lone cow, like its Canadian counterpart last spring, has dramatically altered U.S. agriculture, trade, and markets.
What it is
The clinical signs of BSE include subtle behavioral changes that progress to staggering, wobbling, recumbency, and eventually death. When you examine the brain of an infected animal under the microscope, you see that it is full of holes — like a sponge. Many of these spongiform encephalopathies occur in a variety of species: Creutzfeldt-Jacob disease and kuru in humans, chronic wasting disease in deer and elk, and scrapie in sheep.
Abnormal proteins called prions in the brains of infected individuals cause these diseases. The prions act as a template and alter the normal proteins in the brain, causing a buildup of abnormally shaped proteins.
How it occurs
Prions can be introduced in two ways. The first is spontaneous mutation. The other is from eating nervous system tissue — brain or spinal cord — from an infected animal. Most cows that have developed the disease became infected from eating meat and bone meal that contained brain and spinal cord tissue (and prions) from rendered, infected cows.
In order for a prion from one species to infect another species, the normal proteins must be close enough in shape that the prion can act like a template to affect change. For example, the prions that cause scrapie in sheep do not appear to infect people. However, the prions that cause BSE do, as evidenced by more than 100 human cases in Great Britain.
In the late 1980s, the U.S. banned imports of cattle and cattle byproducts from known infected countries. Then, in 1997, the government banned the feeding of ruminant-derived meat and bone meal back to other ruminants. (Ruminant meat and bone meal can still be fed to other species and, conversely, meat and bone meal made from pigs can be fed to cows.)
Canada banned the feeding of ruminant meat and bone meal to cattle at the same time. Therefore, infected cattle from either country are likely to be older than six years of age.
Yet, holes in the system still exist. Ruminant meat and bone meal can be fed to chickens, and then broiler litter can be fed back to cattle, representing a potential indirect infection hazard for cows. And, despite improved compliance, it is difficult in some cases to ensure that meat and bone meal comes from pigs, not cows. In England, many believe that the BSE outbreak was not really brought under control until all meat and bone meal feeding was banned.
BSE has changed our industry. We are more vulnerable to events occurring thousands of miles away. And, we are reminded once again how important it is to maintain consumer confidence — not just in our own country, but around the world.
Our industry faces many other issues besides BSE — national animal identification, animal welfare, environmental regulations and food safety. In addressing these issues, we need to look beyond the cost to our own individual farms. We need to acknowledge that legitimate consumer and societal concerns exist and, as members of the dairy industry, we need to resolve them.
In order to maintain market access, we must address these issues. The cost of not doing so will far outweigh any short-term savings gained from not taking action.
Brian Gerloff is a veterinarian and operates Seneca Bovine Service in Marengo, Ill.