Resumen:
The aim of the present study was to evaluate the cecal gas production (GP) and methane
(CH4) production as well as cecal fermentation kinetics when corn grain (CG) was replaced
with soybean hulls (SHs) in horse diets in the presence of different levels of Salix babylonica
(SB) extract. Corn grains were replaced with SH at different levels (/kg): 0 g
(control), 75 g (SH75), or 150 g (SH150), with the inclusion of SB extract at: 0, 0.6, 1.2, and
1.8 mL/g dry matter (DM) of substrates. Ration type extract dose interactions were
observed for GP and CH4 production at some incubation hours. Diets containing SH,
without the inclusion of SB extract, increased the asymptotic GP (P ¼ .031) and decreased
(P <.01) the rate of GP and lag time of GP. The inclusion of SB increased (P ¼.009) the rate
of GP, without affecting the asymptotic GP or lag time of GP. Besides, the SH-containing
rations decreased (P < .05) CH4 production, with no effect for SB extract dose. The SH75
ration increased (P < .05) cecal fermentation pH, metabolizable energy, short chain fatty
acids, and gas yield at 24 hours of incubation, but quadratically decreased partitioning
factor at 24 hours of incubation (P ¼ .023), whereas SB extract dose had no effect. It is
concluded that SH-containing rations had higher potential fermentation efficiency and
fermentation kinetics superior to that of CG. The level of 75 g SH/kg DM was the best level
of inclusion to replace 30% CG in the diets of horses. The inclusion of SB extract did not
affect the cecal fermentation kinetics of horse diets containing SH at different levels.