AbstractExperiments were conducted to quantify differences in the rumen microbial activity between goats fed redberry juniper and goats fed alfalfa alone. In Expt. I, goats rumen cannulated and uncannulated goats were fed juniper for 2 h daily for 14 days. Intake and serum metabolites were monitored regularly. Rumen fluid was collected from the cannulated goats on day 10 to assess changes in rumen microbial populations and toxin degradation. In Expt. II, ∼325 ml of rumen fluid was collected from each cannulated goat and was mixed with rumen fluid from goats fed the same diet. Ten goats in Expt. I which were not fed with juniper were inoculated with rumen fluid from either cannulated goats fed juniper or cannulated goats fed only alfalfa. All 10 goats were then fed redberry juniper for 2 h daily for 10 days, and intake was monitored daily. It was shown that in Expt. I, alfalfa intake was similar between treatments and remained constant. Juniper intake increased daily from day 1 to day 10, declined on day 12; intake on day 13 was similar to that of day 10 and increased on day 14. Alfalfa intake was similar for cannulated and noncannulated goats. Juniper intake was lower for cannulated vs. noncannulated goats fed juniper. Serum metabolite levels of γ-glutamyltransferase (GGT), aspartate aminotransferase (AST) and creatinine were elevated in goats consuming juniper. The levels of these metabolites increased across days of collection, while levels remained constant for goats fed only alfalfa. Although serum metabolites were elevated in goats consuming juniper, none were outside the normal range. In vitro toxin degradation of terpenes was similar between treatments. Disappearance of individual terpenes, with the exception of myrcene, and a combination of myrcene, limonene, terpineol and α-pinene, was similar in fluid from goats consuming juniper and fluid from naive goats. Most volatile fatty acids were unaffected by feeding juniper. However, when all 4 terpenes were added in combination, acetic and isobutyric acid levels decreased in goats fed juniper. Acetic acid levels were also lower in goats fed juniper when myrcene was added alone. Adding terpineol to rumen fluid also resulted in lower levels of acetic, butyric and valeric acids. Ammonia levels were similar in goats fed juniper and those fed alfalfa alone. In Expt. II, dosing with rumen fluid had no effect on subsequent juniper intake. Both goats dosed with rumen fluid from goats fed juniper and from those dosed with rumen fluid from goats fed alfalfa alone consumed juniper at similar levels. These results suggest that rumen microbial adaptation alone does not appear to be the physiological processes enabling goats to consume juniper.