Grass Tetany Hazard of Cereal Forages Based upon Chemical Composition1
- H. F. Mayland,
- D. L. Grunes and
- V. A. Lazar2
The occurrence of grass tetany in cattle grazing small grains pastures led us to examine the forage chemical composition and to suggest the relative risk of grass tetany to cattle grazing each forage.
Early spring vegetative growth of wheat (Triticum aestivum L.) and crested wheatgrass (Agropyron desertorum (Fisch.) Schult) was periodically sampled from 3 ✕ 20 m plots established on a fertile Portneuf silt loam (Durixerollic calciorthid). In addition, wheat, oats (Avena sativa L.), barley (Hordeum vulgare L.), and rye (Secale cereale L.) were grown in pots containing Portneuf silt loam in the greenhouse and were harvested once while still vegetative.
Forage samples were freeze-dried and the following parameters determined: total N (Kjeldahl); NO-3 (electrode); Na, K, Mg, and Ca (atomic absorption); S and Cl (x-ray); P (vanadomolybdate); aconitic acid (polarography); higher fatty acids and ash alkalinity (both by titration). Estimated blood-serum Mg values were calculated from a generally unavailable Dutch nomograph of forage N ✕ K and Mg values. The nomograph is included in this paper to enhance its availability.
Wheat forage seemed to pose a greater tetany hazard than the wheatgrass because wheat had lower values for Ca and higher values for K, K/(Ca + Mg), aconitic acid, ash alkalinity, and HFA. The estimated tetany hazard of the cereal forages was wheat > oats = barley > rye. This ranking corresponded to the other of blood-serum Mg levels predicted from the Dutch nomograph. Wheat forage was lowest in Mg, while rye forage was highest in Mg and Ca, and lowest in K and N. Aconitic acid represented a large portion of the total organic acids in oats, rye, wheat, and wheatgrass, but only traces were found in barley.
The frequent occurrence of grass tetany in cattle grazing wheat forage may result because of lower Mg and Ca levels and higher K, N, ash alkalinity, and HFA levels in this forage compared to other cereal forages.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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