Response to Selection for Reduced Grass Tetany Potential in Crested Wheatgrass

Asay, K.H. and Mayland, H.F. and Clark, D.H. (1996) Response to Selection for Reduced Grass Tetany Potential in Crested Wheatgrass. Crop Science. 36:895-900.

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Abstract

Grass tetany (hypomagnesemia) has caused substantial economic
losses in ruminant animals grazing crested wheatgrass (Agropyron
spp.) and other cool-season (C3) grasses. This malady is most prevalent
in early lactating animals grazing forage that is deficient in Mg, Ca,
and carbohydrates and with high levels of K. The K/(Ca + Mg) ratio
expressed as moles of charge is often used to estimate the grass tetany
potential of forage samples. Previous studies have shown that heritable
variation exists in crested wheatgrass populations for traits associated
with grass tetany, and research was conducted to determine the genetic
response to selection for these traits. Selections were made during
1985 from two crested wheatgrass breeding populations in Utah (`I-28'
and Hycrest) based on a reduced grass tetany potential (RTP) index,
which incorporates the K/(Ca + Mg) ratio along with concentrations
of Ca, Mg, and K. Mean values for the K/(Ca + Mg) were reduced by
5% in 1-28 and 11% in Hycrest after one cycle of selection. Narrow-sense
heritability values based on actual genetic advance and parent-progeny
regression ranged from 0.62 to 0.82 in analyses of data combined
across two sampling dates and two years (1988 and 1989). Genetic
response to selection on the basis of RTP index was closely associated
with the K/(Ca + Mg) ratio and concentrations of Ca and Mg but
not with levels of K. Correlations between the K/(Ca + Mg) ratio
and crude protein content and digestibility suggested that selection
for RTP would likely be accompanied by improved forage quality in
the Hycrest breeding population.

Item Type:	Article
NWISRL Publication Number:	0908
Subjects:	Irrigated crops > Grass forage > Chemistry Mass Import - autoclassified (may be erroneous)
Depositing User:	Dan Stieneke
Date Deposited:	20 Nov 2010 21:54
Last Modified:	22 Nov 2016 22:50
Item ID:	662
URI:	https://eprints.nwisrl.ars.usda.gov/id/eprint/662