One of my best customers asked me last week if there is anything we can add to pig feeds to make sure exposed animals will not get infected by the PED virus. Obviously, this is someone in the U.S., where pig producers are looking into anything that can help, given no cure or vaccine is currently available.
With bacteria, we have become accustomed to think in terms of antibiotics, organic acids, zinc oxide, copper sulphate, and other such antimicrobial agents -- all used effectively in pig feeds. Indeed, used at the right concentration and time, such ingredients can prevent bacterial infections. This is why the antimicrobial business is such a tremendous industry worldwide. Also, most nutritionists, although not trained in veterinary matters, tend to know quite a bit about bacterial infections and how to handle them.
When it comes to viruses, things are very different. Like in humans, there are no medicines that can prevent a viral infection -- or we would not suffer from flu every winter. Only vaccines can do that, and only if they target the same strain of virus as that invading an organism. Thus, when it comes to feed, nutritionists raise their hands, as absolutely no ingredient (at least known to me) can stop an animal from contacting a virus, inclusive of PED virus.
But, like in human medicine, certain food/feed ingredients can alleviate the symptoms of a viral infection (chicken soup versus flu), but here, we are discussing a post-infection feeding strategy. Additionally, strengthening the immune system to reduce the impact of a viral disease is something we can accomplish through nutrition in the pre-infection period.
In brief, no ingredient can stop pigs getting the PED virus. Nutritionists can be useful in designing a pre- and post-infection nutrition program, but for the rest, we are still waiting the veterinarians to develop a successful vaccine.