By genetically removing a particular protein, scientists have developed cattle that seem to be resistant to mad cow disease, according to a report in the journal Nature Biotechnology.

Dr. Juergen A. Richt with the United States Department of Agriculture in Ames, Iowa and colleagues generated cattle lacking the prion protein (PrP) and monitored them for growth and general health status from birth to 20 months of age.

PrP in its normal formation does not cause disease in cattle, but when it takes on a configuration containing misfolds, it results in mad cow disease, also known as bovine spongiform encephalopathy. Because the function of the normal PrP is not clear, it was not known if animals without this protein would be healthy.

To investigate, Richt's group first developed mice lacking the gene for PrP. No growth or developmental abnormalities were seen. Next, they moved on to cattle.

The animals also displayed normal growth and development and had no abnormal blood tests, the researchers note. Moreover, loss of PrP did not seem to harm the animals' immune systems or their reproductive ability.

Early tests suggested that these animals are resistant to the development of mad cow disease. The authors note, however, that full testing will take at least 3 years.

SOURCE: Nature Biotechnology, December 31, 2006 (advance online issue).