A family of PCR assays is disclosed for determining, both qualitatively and quantitatively, presence of material from a predetermined species source and for quantifying the amount of such material. The assays are based respectively on SINEs uniquely characteristic of pig species, cow species, chicken species, and ruminant sub-order, and having a high copy number. The assays disclosed permit rapid, inexpensive evaluation of meat samples to facilitate elimination from their diet of pork or beef by persons desiring to avoid such food sources; as well as the assay of cattle feed to determine presence therein of ruminant-source proteins, which are a potential source of bovine spongiform encephalopathy (BSE), commonly referred to as "mad cow disease." The assays amplify the predetermined unique SINEs and the resulting amplified mixture is then evaluated qualitatively by electrophoresis on gel containing ethidium bromide or quantitatively by SYBR Green-based detection or TaqMan chemistry. The invention also extends to kits, primers, and other products used in connection with the assays. The amplicons are selected to be from about 100 to 170 bp long.