The amount of a endogenous retrovirus group V member 1 Env polyprotein when measured in blood serum. The trait is level of endogenous retrovirus group V member 1 Env polyprotein in blood serum (OBA_2044558, an Ontology of Biological Attributes identifier). Also known as: blood serum endogenous retrovirus group V member 1 Env polyprotein amount.