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Background: plant extracts of Forsythia suspensa, which contain pinoresinol, have been proposed as an alternative to antibiotics due to their antioxidant, anti-inflammatory, and microflora modulating effects. Objective: to evaluate the effects of dietary F. suspensa on feed utilization, rumen fermentation, blood parameters and immune response of Korean native goats (Capra hircus). Methods: a total of nine Korean native goats were assigned to one of three dietary treatments: 1) a basal diet without F. suspensa, 2) a basal diet added with 0.25% F. suspensa, or 3) a basal diet added with 0.50% F. suspensa. A change-over design was used in three consecutive periods to give 9 replicates per treatment. Each period lasted 18 days, including 15 days of adaptation to feed and environmental conditions and three days of total collection of feces and urine. Rumen fluid and blood samples were also collected. Nutrient digestibility, nitrogen retention, ruminal content, and blood metabolites-including immunoglobulins-were measured. Results: F. suspensa supplementation had no effect on nutrient digestibility, whole body nitrogen retention rate, ruminal pH, acetate, propionate, isobutyrate, butyrate, isovalerate, or valerate content (p>0.05). However, F. suspensa supplementation decreased total volatile fatty acids (VFA) concentration compared with the control diet, regardless of F. suspensa concentrations (p<0.05). Goats fed a diet containing 0.25% F. suspensa had greater alkaline phosphatase (ALP) concentration than those fed a control or a diet with 0.50% F. suspensa (p<0.05). Feeding different concentrations of dietary F. suspensa did not influence plasma IgA and IgM levels (p>0.05), although goats receiving both 0.25% and 0.50% F. suspensa diets had greater plasma IgG than those fed the control diet (p<0.05). Conclusions: supplementation of 0.25% F. suspensa significantly decreased total VFA concentrations and increased plasma IgG in Korean native goats, compared with those fed the control diet. [ABSTRACT FROM AUTHOR]