Root Temperature and Calcium Level Effects on Winter Wheat Forage: II. Nutrient Composition and Tetany Potential

Wheat pasture poisoning is a metabolic deficiency of Ca, and sometimes Mg, in ruminants. It occurs particularly in the spring, when K and N concentrations in the shoots, and the equivalent ratio of K/(Ca+Mg) in the forages, increase suddenly. To determine the effects of an increased root temperature and four Ca levels on the forage quality of winter wheat ( Triticum aestivum L. ‘Centurk’), seedlings were grown under three root temperature regimes (constant 8 °C, constant 16 °C, and increasing from 8–16 °C), in nutrient solutions with four Ca levels (0.2, 0.6, 2.0, and 5.0 m M ). Plants grown at 8 °C root temperature had significantly lower Ca, Mg, K, and N concentrations in the shoots, and a significantly lower equivalent ratio of K/(Ca + Mg), compared to those grown at 16 °C. Plants transferred from 8 to 16 °C had significantly increased Ca, Mg, K, and N concentrations in the shoots over time, as levels changed from those characteristic of low root temperature plants to those characteristic of high root temperature plants. Plants transferred from 8 to 16 °C also had an equivalent ratio of K/(Ca + Mg) that increased 1 wk after the transfer, indicating a greater tetany hazard. The doubling in forage K and N concentrations, and the increase in the equivalent ratio of K/(Ca+Mg) as root temperatures increased from 8 to 16 °C, are similar to those found in field‐grown plants at the time of tetany for grazing beef cattle. Thus, root temperature could be a key environmental factor involved in tetany, modifying the nutritional quality of winter wheat.