In whole-crop maize silages with atypical smell and decreased acceptance by ruminants, high concentrations of the volatile organic compounds ethyl acetate (EA) and ethyl lactate (EL) were detected. The aim of this study was to evaluate the impact of different concentrations of ethyl esters added to forage on preference and short-term feed intake of goats. In the first of three trials, whole-crop maize silage was supplemented with different concentrations of EA and EL and then vacuum-stored before use. Forages sampled during the preference trial showed a good recovery of EL with a high accordance of target (naturally formed + supplemented) and analysed concentrations. Supplemented EA was not recovered, making transient storage of substrates before use in feeding trials equivocal. However, four treatments with different concentrations of EL (approximately 330, 560, 920 and 1300 mg/kg dry matter (DM)) were used for the preference trial. In Trials 2 and 3, EA and EL (with and without ethanol, respectively) were added to grass hay directly before offering the feed, each in concentrations of 0, 600 and 1200 mg/kg DM to have six treatments each. In all trials, each possible combination of treatments was offered to Saanen-type wethers (n = 10, Trial 1; n = 5, Trials 2 and 3) as free choice in preference trials. In Trial 1, there was only a weak impact of EL on preference behaviour as goats avoided medium EL concentrations, but did not avoid silages with higher concentrations. In Trials 2 and 3, there was no influence of added volatiles on short-term DM intake and preference at all. It can be concluded that it is unlikely that ethyl esters as single substance or in combination with ethanol affect preference behaviour and feed intake of ruminants. Possibly a combination or still unidentified fermentation products cause avoidance instead of a single compound.
Keywords: Esters; feeding preferences; fermentation products; ruminants; silage quality; volatile compounds.