Shade-induced Grass-Tetany- Prone Chemical Changes in Agropyron desertorum and cinereus

Grass tetany, a magnesium (Mg) deficiency in grazing ruminants, often occurs simultaneously with periods of reduced solar radiation levels. The objective of this study was to determine if reduced radiation levels produce a chemical composition in grass indicative of a tetany-prone forage. Two grass species were exposed to three radiation levels (8, 25, and 100% of actual) by shading with burlap cloth. The vegetatively growing forage was harvested at weekly intervals over a 5-week period during early spring. Shaded forage had higher concentrations of Mg than did unshaded forage. However, shaded forage compared to forage grown in full sunlight would likely result in less Mg being available to the animal. The hypothesized inverse relationship between radiation and the incidence of grass tetany in Idaho, Nevada, and Utah is supported by field observations