Mae’r gwaharddiad ar fewnforio cig oen o Brydain i UDA yn dyddio o 1996 yn sgil y clefyd Enseffalopathi Sbyngffurf Buchol (BSE).  Cafodd y gwaharddiad ei estyn mewn rhai gwledydd i gig dafad gan fod clefyd o’r un teulu – Enseffalopathïau Sbyngffurf Trosglwyddadwy (TSE) - yn effeithio ar ddefaid.
The ban on British lamb to the USA has been in place since 1996 following an outbreak of bovine spongiform encephalopathy (BSE). The ban was extended in some countries to sheepmeat on the basis that a related sheep disease belongs to the same family of TSE (Transmissible Spongiform Encephalopathys) diseases.