Transmission of prion brain diseases such as bovine spongiform enecephalopathy (BSE) — also known as mad cow disease — and human variant Creutzfeldt-Jakob disease (vCJD) is generally attributed to the consumption of the brain or organ meat of infected animals but new research demonstrates lambs exposed to milk from prion-infected sheep with inflamed mammary glands can develop prion disease as well. The research has major implications for human and livestock health.