The two dairy farms were under investigation after a cow from one of the farms was found to be infected by bovine spongiform encephalopathy or "mad cow."
The elderly cow was found during random testing and was subsequently disposed of by health inspectors, said Reuters.
Though the farms were said to be safe, investigators are still looking for about a dozen other animals that may have come into contact with the infected cow.
“Of several hundred potential birth cohort cattle, the focus of the tracing is on a small number,” the USDA said, reported Business Week.
“The remaining potential cohorts are no longer alive or have otherwise been ruled out.”
CNN reported that the infected cow gave birth twice, one a stillborn and the other tested negative for the disease.
Last month's mad cow scare was said to be caused by an atypical strain of the disease that is not dangerous to humans.