Influence of Salix babylonica extract in combination or not with increasing levels of minerals mixture on in vitro rumen gas production kinetics of a total mixed ration

Plant extracts, with high concentrations of secondary metabolites, are good candidates for enhancing nutrient utilization (Patra et al., 2006; Cedillo et al., 2014). Administration of Salix babylonica (SB) extract to ruminants as feed additives modified in vitro ruminal fermentation in lambs (Jiménez-Peralta et al., 2011; Salem et al., 2014b), improved in vivo digestibility as well as average daily gain of lambs (Salem et al., 2011a, 2014b) and milk production (Salem et al., 2014a). Some plant extracts also improved animal growth and nutrient digestion (Mapiye et al., 2010; Salem et al., 2011a) due to positive impacts of their secondary metabolites on activity of ruminal microorganisms (Jiménez-Peralta et al., 2011) and/or increased amino acid flow to the duodenum (Mueller-Harvey, 2006). This can result in more muscle deposition and, consequently, heavier carcasses (Gleghorn et al., 2004) and improved meat quality (Mapiye et al., 2010).The aim of this study was to determine the effects of increasing levels of two feed additives composed of Salix babylonica (SB) extract and minerals mixture (MM) or their combination on in vitro gas production (GP) and dry matter (DM) degradability of total mixed ration (TMR; 50 concentrate: 50 corn silage, on DM basis). Combinations of four levels of SB extract (0, 0.6, 1.2 and 1.8 mL/g DM) with four levels of MM (0, 0.5, 1.5 and 2.5 g/100 g DM) were evaluated in a completely random design. Samples of TMR (1 g) were weighed in 120 mL serum bottles with addition of SB extract and/or MM. Then, 10 mL of particle free ruminal fluid were added followed by 40 mL of the buffer solution. The GP was recorded at 2, 4, 6, 8, 10, 12, 24, 48 and 72 h of incubation. Addition of SB extract, without MM, increased (P