The US Department of Agriculture's (USDA) Agricultural Research Service (ARS) has published the initial results of a research project involving prion-free cattle under which ARS’ scientists evaluated cattle that have been genetically modified so they do not produce prions, and determined that there were no observable adverse effects on the animals' health.
"These cattle can help in the exploration and improved understanding of how prions function and cause disease, especially with relation to bovine spongiform encephalopathy, or BSE," said Edward Knipling, administrator of ARS.  "In particular, cattle lacking the gene that produces prions can help scientists test the resistance to prion propagation, not only in the laboratory, but in live animals as well."

Prions are proteins that are naturally produced in animals. An abnormal form of prion is believed to cause illnesses called transmissible spongiform encephalopathies (TSEs), the most well-known of which is BSE.    

ARS studied eight Holstein males that were developed by Hematech Inc., a pharmaceutical research company. The evaluation of the prion-free cattle was led by veterinary medical officer Juergen Richt of ARS' National Animal Disease Center (NADC) in Ames, Iowa. The evaluation revealed no apparent developmental abnormalities in the prion-free cattle.
Mr Richt said, "The cattle were monitored for growth and general health status from birth up to 19 months of age. Mean birth and daily gain were both within the normal range for Holsteins. General physical examinations, done at monthly intervals by licensed veterinarians, revealed no unusual health problems."

Further testing will take at least three years to complete.