The findings, published in the Journal of Animal Science, show that sheep infected with scrapie and cows infected with BSE have eleveated levels of manganese in their blood before clinical syptoms appear.
The study also reveals that scrapie-resistant sheep produce elevated levels of the metal when "challenged" with the disease.
This suggests that elevated manganese levels in the blood and central nervous system are caused by the sheep's initial response scrapie.
The research raises the possibility of using manganese levels in the blood as a diagnositic marker for scrapie and BSE. At present, only post mortem examination of brain tissue gives a certain diagnosis.
"Definite diagnosis of prion disease is currently only possible post-mortem," said Professor David Brown from the University of Bath who led the study with colleagues from the universities of Hull and Edinburgh.
"These findings suggest that elevated blood manganese could be used as a robust diagnostic marker for prion infection, even before the onset of apparent clinical disease.
"In practice, however, it would be difficult implement a widespread screening programme, given that the mass spectrometry we use to measure levels is expensive and labour intensive."
It is the first time that tissue from farm animals infected with prion diseases has been studied in this way.
Scrapie and BSE are nuerogenerative diseases that affect the brain and nervouse system of sheep and cows respectively. They are transmitted by mis-formed prion proteins which cause loss of brain cell in different regions of the brain, leading to impairment of brain function.