Based on empirical observations from commercial farms that well preserved, but odd-smelling maize silages may cause problems regarding feed intake and milk yield by dairy cows, volatile organic compounds (VOC) were analyzed in recent studies. The aim of this paper was to summarize the results concerning the occurrence of VOCs in silages and the effects of silage additives on their formation. Elevated levels of ethanol, ethyl acetate (EA) and ethyl lactate (EL) as well as propanol and propyl acetate (PA) occurred in maize and whole crop silages, grass/ grass-legume-mixtures silages, furthermore in sugar cane silages. Ester and ethanol levels were highest in silages stored under strict anaerobic conditions. In conclusion it can be stated that the ester concentrations were strongly correlated with the ethanol concentration and the silage pH. Results from ensiling experiments on the effects of silage additives on ester formation in different ensiling materials clearly indicated that chemical products containing active ingredients with specific antifungal effects can significantly reduce ethanol and ester concentration. Salts of sorbic, benzoic or propionic acids or mixtures are effective treatment for reducing VOC production. Buffered formic acid-containing products stimulated it due to an increase in ethanol content. A survey was carried out to investigate the incidence of VOCs in maize silages from German dairy farms and to monitor the concentrations of ethanol, n-propanol and the corresponding esters ethyl acetate, ethyl lactate and propyl acetate. With increasing compaction the contents of VOCs increased and their concentration depends on the sampling site in the silo.
