Effects of propionic acid added to supplemental corn on utilization of complete ensiled diets by lactating dairy cows

Two bottom unloading silos were filled with alternate loads of alfalfa (Medicago sativa L.) and ground shelled corn grain mix (1:5, grain:forage, wet basis) to determine effects of propionic acid added to supplemental corn on performance of lactating dairy cow consuming a complete ensiled diet. One silo received grain mix containing 1% propionic acid. Each of two groups of six lactating cows was fed one of the complete ensiled diets supplemented with high moisture corn, dried-shelled corn, or no supplemental corn for 4 mo. Cows that consumed the acid-treated diet produced less milk, fat, and protein than cows consuming the untreated diet. Supplemental high moisture corn and dried shelled corn increased milk and protein yields, and high moisture corn increased fat yields compared to the unsupplemented. Daily variation of the ratio of grain:forage indicated that alternate load additions of forage and grain resulted in poor mixing of ration components and may be related to some of the differences in performance.