I think the keyword here is extreme biosecurity. For coccidiosis, extreme humidity is the predisposing factor. In high humid climate for open housing ,vaccination or strategic medications will go a long way in cutting the life cycle of coccidia. Pre and probiotic is good as regards necrotic enteritis but this is effective at the build up or initializing or lag phases.

Dr. Charles Ibe, I agree about the biosecurity. The use of agents that induce lysis of sporulated oocysts reduces the number of resistant ones and increases the efficacy of both vaccines and coccidiostatics. High humidity, as well as low humidity, stops the sporulation process.

Hi to all:
In good husbandry management, both diseases have to be prevented. For coccidiosis, it includes inducing good immunity by vaccination or by using coccidiostat in rotation or shuttle program, and when there are clinical signs and mortality, treatment is the only way to be done. Depending on the region of intestine affected and drug sensitivity.
For necrotic enteritis, disease management practice includes coccidiosis prevention, gut health management, and if there is mortality, antibiotic affecting gram positive must be used. But when the coccidiosis predisposes to necrotic enteritis management, the condition is complicated and treatment of coccidiosis is the priority.