Oxidized milk with a cardboardy or metallic taste is more prevalent in milk in late winter or spring.
Causes are different than for light induced flavor of milk in stores, although the taste is similar.
Increased susceptibility of milk to oxidation is due primarily to less antioxidant in the milk. This is because of the decreased amount of vitamin E, an oxidant, in stored forages, which reduces the amount in milk. Causes of oxidized flavor on farms or in processing plants include equipment surfaces which are not clean, minerals in the water supply, acid water and copper tubing, use of chlorine sanitizers, stored forages low in vitamin E, and feeding too much fat from soybeans, cottonseed or feed with added fat, especially vegetable oils. It is usually necessary to correct all causes before the off-flavor will disappear. Don't expect feeding vitamin E to overcome too much copper or iron in the water supply used to wash equipment, or milking equipment surfaces which are not clean.