RESUMO
Date kernels (DK) are cheap by-products rich in energy and phenolic compounds. It can be used as an alternative to the conventional sources of energy in ruminant diets while reducing methane (CH4) production. Using a semi-automated gas production (GP) system, the initial pH of buffered rumen liquor was adjusted to 5.5 and 6.8. Five experimental diets were evaluated, control (0% DK), and DK25, DK50, DK75, and DK100 presented 25, 50, 75, and 100% replacement of maize by DK, respectively. Of the 16 phenolic compounds detected in DK, protocatechuic, p-hydroxybenzoic and catechin were the most abundant. At pH 6.8, the control diet recorded higher (p < 0.05) GP values throughout the first 12 h incubation than all other DK diets, while at 5.5 pH, DK50 displayed the highest (p < 0.05) GP at 3 and 6 h compared to all other diets. At either pH conditions, all DK diets reduced (p < 0.05) CH4 compared to the control without affecting protozoal counts. At 5.5 pH, DK diets showed enhanced (p < 0.05) nutrients degradability compared to control. DK modified (P < 0.05) the fermentation patterns toward more propionate than the control under either pH conditions. Substitution of maize by 50% DK was highly recommended in ruminant diets.