Reference values for a field test to estimate inadequate glutathione peroxidase activity and selenium status in the blood of cattle.

A clinical screening procedure was developed for estimating glutathione peroxidase (GSH-Px) activity and selenium status in the blood of dairy and beef cattle. The test is based on the rate of defluorescence under long waveform UV irradiation of reduced nicotinamide adenine dinucleotide phosphate in a coupled enzyme reaction involving glutathione reductase. Defluorescence rates were significantly correlated with blood GSH-Px activity and blood selenium concentrations as determined by conventional laboratory procedures. Blood selenium concentrations and blood GSH-Px activity in several herds were compared with the selenium content of the complete ration consumed to establish reference or base-line values for these blood characteristics under field conditions. The GSH-Px screening procedure provides rapid results, is relatively inexpensive, and appears to be useful in differentiating between the reference values and grossly inadequate selenium status in cattle.