Feeders are VERY high prone to diseases and parasites. It is best to buy a 10g tank or tub and use it to quarantine all feeders. Not just a few feeders, either, but make sure you have enough.
What sandtiger was referring to is stocking the feeder fish with high quality foods such as frozen brine, bloodworms, or mysis shrimp before feeding to your bass, so when the bass eat the feeders they also get a belly of quality nutrition. I suggest cutting back on the feeders slowly until your fish are literally begging for food, then try something like market shrimp, silversides, crayfish, etc. to try to wean them off of feeder fish..... Or you could always breed your own feeder fish!