Richt, J. A., Kasinathan, P., Hamir, A. N., Castilla, J., Sathiyaseelan, T., Vargas, F.,... Kuroiwa, Y. (2007). Production of cattle lacking prion protein. Nature Biotechnology, 25(1), 132. Doi: 10.1038/nbt1271. Retrieved August 22, 2012.