We understand that it is totally forbidden within the same animal species and not only for the protein, but for all slaughterhouse by-products. Therefore, sebum can not be used in ruminants, lard can not be used in pigs, etc. According to the European Commission

http://europa.eu/rapid/press-release_MEMO-04-107_en.pdf

MEMO / 04/107
Brussels, 6 May 2004
QUESTIONS And Answers on animal by-products

Intra-species recycling (cannibalism) ban The regulation extends the current ruminant intra-species recycling (cannibalism) ban to other species. Porcine animal by-products can not be fed to pigs and animal poultry by-products. However, derogation is provable for the case of fish and fur animals subject to strict controls by the competent authority.

«El reglamento extiende a otras especies la prohibición, ya antes aplicable a los rumiantes, del reciclaje (de subproductos) dentro de la misma especie…»

More clear water!