High magnesium minerals in the spring are necessary to prevent grass tetany which is a muscular disorder that can be fatal. The grass is growing so rapidly that it has little nutrition in it, such as magnesium. Providing magnesium in the early spring is a safeguard against this nutritional deficiency.
Fescue Foot is a condition brought on by the toxins found in the fungus in endophyte infected fescue. It reduces blood flow to the extremities and they slough off. Feet, tails, and ears can be affected. Dun is dead on as usual on this this one. Dilute the grass. Encourage bermuda, bahia, dallisgrass, and crabgrass to grow. Of course, the old standby is white clover. Some cattle adapt to the infected fescue, some do not. Some research has shown that Brahman type cattle may adapt better than some other breeds. However, fertilize in late spring or early summmer to encourage summer grasses to emerge through your fescue sod.