The ability of cattle to resist the many disease processes to which they are exposed is truly amazing. And yet, when several adverse factors combine, this resistance can be overcome and result in a herd disaster which is just as amazing. This discussion will be broken down into four major areas. But it is the combined functioning of all four areas that actually provides disease resistance.
Bagley, Clell, "Disease Resistance in Cattle" (1997). All Current Publications. Paper 447.