We've had feed affected by mould on several occasions - if undetected it can cause serious problems in a breeding herd, leading to small litters and abortions. We now always check every feed sack by sticking our noses into it when first opened and sniffing hard, and always look at each bucketful in a good light before we lob it over the fence. Mould will present as a slightly chalky look, sometimes greyish-green, on the surface of the pellets. It's often caused by the feed being bagged at the mill when conditions are very humid, thus sealing the damp air in with the pellets. Our feed merchant has always arranged for the bags to be replaced by the merchant concerned. Ours are stored on pallets in a secure block and tin building, so we know the feed hasn't been contaminated at this end.