FERTILIZING TALL FESCUE PASTURES WITH PHOSPHORUS TO PREVENT GRASS TETANY IN GRAZING BEEF COWS

摘要

Grass tetany is a nutritional disorder of ruminants caused by low levels of Mg in the diet. The disease is common during early spring when cows graze cool season grasses with low Mg concentrations. Previous research at the University of Missouri indicated that P fertilization of tall fescue increases the Mg concentration of the grass. Therefore, a trial was initiated to determine if P fertilization of tall fescue increased the Mg status of animals grazing those pastures. Another objective was to determine if P fertilization of tall fescue provides the same protection against grass tetany as free-choice Mg supplements. Blood and cerebrospinal fluid samples were collected to determine the Mg status of the animals. At the end of the 56 d trial, the blood serum Mg concentration of cows in the P fertilized and Mg supplement groups was 20 and 19 ppm, respectively. These levels were 20% greater than the blood serum Mg concentration of cows in the control group. There were no differences in cerebrospinal fluid Mg concentrations. These results indicate that cattlemen might reduce outbreaks of grass tetany on their farms by maintaining at least 30 lb/ac soil P in their tall fescue pastures. Furthermore, P fertilization of tall fescue compares favorably to free choice Mg supplements in grass tetany protection.