Dex is fine to use in cattle. It has a steroidal effect, a little more potent than Predef. I usually only use it when I'm giving a newborn calf a kick start, or trying to save him from dying. e.g. a calf is born from a hard pull, give it 5cc under the tongue in the fleshy tissue. The blood is more concentrated there.
Banamine is a better anti-inflamatory(in my book). Be careful to not give it too long (like more than 1-1.5cc/100 lbs for more then about 5-7 days). It can take their kidneys out.
Dexamethasone is a glucocorticoid - it is very much like cortisol - it has many uses, for example since fetal cortisol is the trigger for labor in the pregnant cow it can be used to induce labor. It is (as I am sure you are aware) a drug that requires a prescription for use. Although useful it is not without potential problems - especially if used repeatedly - these include ulcers, dehydration, and immune suppression (increased risk of infection) -