Aerobic exposure of grass silages and its impact on dry matter intake and preference by goats

The effect of aerobic exposure of grass silages on short-term feed intake and preference by goats was studied. Eight grass silages differing in dry matter (DM) (25% and 33%), chop length (short and long) and compaction pressure at ensiling (0.1 MPa and 0.2 MPa) were exposed to air for eight days. Chemical analyses were conducted in 2-day (d) intervals (d0, d2, d4, d6 and d8 after silo opening) for proximate constituents, fermentation products and other volatile compounds as well as determination of microbiological status (yeasts, moulds and aerobic mesophilic bacteria). Furthermore, d0- to d8-silages were stored anaerobically in vacuum-sealed plastic bags for use in preference trials. After aerobic exposure, eight preference trials with Saanen-type wethers (n = 5) were carried out, where each possible two-way combination of silages and a standard hay (n = 15) was offered for 3 h. Data were analyzed using the SAS procedure Multidimensional Scaling, analysis of variance and correlation analysis between silage characteristics and DM intake (DMI). All silages were aerobically stable during the examination time. In trials with 33% DM-silages, DMI decreased at d6 or d8 (in each of two trials) of aerobic exposure. Silage that had been exposed to air for 8 d was avoided in each case with a reduction (mean ± standard deviation) of 50 ± 6.7% in comparison to the freshest silage. Low-DM silages showed signs of malfermentation with higher concentrations of butyric acid and ammonia-nitrogen (NH3-N). Both DMI and the impact of aerobic exposure on DMI were lower. Mean decrease in DMI after 8 d of aerobic exposure was 20% (±11.0%). Products from protein and amino acid degradation (NH3-N, butyric acid) were negatively correlated to DMI (r = −0.55 and −0.59; P < 0.001). It was concluded that in well-fermented silages, aerobic exposure for a length of time that is of practical relevance does have a negative impact on short-term DMI and preference by goats, even if silages are at an apparently low stage of deterioration. It is assumed that goats can detect subtle differences caused by aerobic exposure, sometimes even before an increase in temperature or changes in chemical composition occur. After a 1-d exposure of each variant, goats were able to differ between forages and showed preference or avoidance for different silages, with a high correlation between initial and total DMI. Therefore, results showed the potential for 30 min measurements in short-term preference trials, as goats remember post-ingestive feedback from the adaptation period.