Genetic Variability for Elements Associated with Grass Tetany in Russian Wildrye

Grass tetany (hypomagnesemia) may be an important factor productivity of animals grazing Russian wildrye [Psathyrostachys (Fisch.) Nevski]. This malady is associated with low concentrations in the forage of Mg and Ca, and high for K and K/(Ca+Mg). We studied the genetic variablity in a wildrye breeding population for mineral elements that to grass tetany in ruminants. Forty-five progeny lines, established spaced plants in a randomized complete block, were at the pre-boot and boot stages in each of 2 years and for Mg, Ca, K, and P. Although seasonal variation was, K/(Ca+Mg) of the progeny lines ranged from 3.2 to 4.6, above the 2.2 level at which a 5% incidence of grass tetany has found in dairy cattle. With few exceptions, progenies differed all traits evaluated. Differences among progenies were relatively over harvests for all traits. A reduced tetany (RTP) was computed as the sum of normalized Mg and of K/(Ca+Mg) values, providing an estimate of the grass risk for individual progeny lines. The variation among, and the magnitude of broad-sense heritability estimates RTP (0.48) and K/(Ca+Mg) values (0.31), indicate that mineral composition of this breeding population can be altered through. The high K/(Ca+Mg) values in the population suggest it may be helpful to introduce genetic factors conditioning grass tetany potential from other sources. Intercharacter suggest that breeding for higher levels of Mg will be by increased Ca and, to a lesser extent, increased K.