Linking forage choice behavior of goats with the metabolome of contrasting silages

The interrelationships between silage preference of ruminants and compounds that may affect forage choice are not yet fully enlightened. Analysis of the forage metabolome in addition to conventional chemical analysis and preference trials can provide new insights. Six silage treatments each of alfalfa (AL) and red clover (RC), with different dry matter concentrations (222-391 g/kg), silage additives, and intended addition of soil, were produced in quadruplicate to obtain a range of qualities. After 120 d of ensiling, silages were sampled for chemical analysis, vacuum-packed, and refrigerated for subsequent preference trials with goats. Within 21 d, each possible combination of 2 silages and an AL hay that served as control (n = 21) was presented to goats (Saanen-type wethers, n = 8, body weight 105 ± 2.7 kg) for 3 h for ad libitum intake. Comparisons among means for 3-h dry matter intake (DMI) for forages offered in choice situations were made using variance analysis, including terms for treatment and animal and the Waller-Duncan k-ratio t-test to separate means. The most preferred and avoided treatments of AL and RC silage amounted to 863, 858, 226, and 282 g DMI/3 h, respectively. To further explore relations between silage composition and preference, a metabolome analysis of the most preferred and most avoided AL and RC treatments were conducted. Metabolites (all low molecular weight molecules) were analyzed by a nontargeted metabolite profiling in the range of 50-1,700 Da. Metabolites showing the most distinct difference between preferred and avoided silages were identified by partial least squares discriminant analysis. In the 2 selected treatments of each plant species (those that were most different in forage preference), more than 6,400 compounds were detected and 2,010 were identified. Between preferred and avoided treatments, 934 of the detected compounds differed in RC and 1,860 in AL, of which 475 were altered in both plant species (251 were reduced and 186 were increased; only 38 behaved contrarily, meaning that they were increased in one substrate and decreased in the other). The database provides a useful foundation for the approach of explaining silage preference by ruminants.