Grass tetany (hypomagnesemia) has caused severe economic losses
in ruminant animals grazing cool-season grasses, including Russian
wildrye [Psathyrostachys juncea (Fisch.) Nevski]. The malady has
been associated with deficiencies in Mg, Ca, and carbohydrates, and
high levels of K. The K/(Ca + Mg) ratio (KRAT), expressed as moles
of charge, is often used to express the grass tetany potential of forage.
Development and use of new cultivars with an improved balance of
the associated minerals would be an economical approach to reduce
the incidence of grass tetany. Objectives of this study were to characterize
the genetic variability, genotype by environment interactions,
and intercharacter relationships for P, K, Ca, Mg, KRAT, crude protein
(CP), neutral detergent fiber (NDF), and in vitro dry matter
digestibility (IVDMD), among 21 clonal lines of Russian wildrye and
their polycross progenies. Evaluations were made for 2 yr at three
diverse locations in the USA and Canada. The clonal lines were
derived from cultivars and plant introductions. Although the clone x
location interaction was usually significant, differences among the
clonal lines were significant for K, Ca, Mg, and KRAT, and three
forage quality estimates of CP, NDF, and true IVDMD. Although
the magnitude of the genetic variability among the progenies was
substantially less than that found among the clonal lines, we conclude
that the grass tetany potential, CP, NDF, IVDMD, and P concentration
of this breeding population can be altered through breeding.
Opportunities for genetic improvement in forage quality were particularly
favorable for CP. Genetic correlations among the clonal lines
suggested that selection for higher levels of CP would be accompanied
by increased K, Ca, Mg, and IVDMD and reduced KR AT and NDF
