The present invention provides antibodies that specifically bind with a high degree of binding affinity to a native ungulate PrPC and/or a denatured ungulate PrPSc, but not to a native ungulate PrPSc. Preferred antibodies find native bovine PrPC and treated PrPSc but not native bovine PrPSc and can be used in an assay to determine if a sample is infected with infectious prions, i.e. PrPSc.