The objective of the present study was to evaluate the effect of black pepper (Peppee nigrum) essential oil (BPEO) on in vitro gas production parameters of alfalfa hay, barley grain or sugar beet pulp. The samples were left untreated or treated with BPEO (0.4 ml/g DM). The gas production data were fitted using an exponential equation of P = b (1-e -ct ), where b is the volume of gas produced, c is the fractional rate constant of gas production (/h), t is the incubation time (h) and P is the volume of gas produced at time t. A significant difference of gas production parameters (p<0.05) was observed among the feed samples evaluated in the present study. Present results indicate BPEO caused a significant increase (p<0.05) in both b and c fractions of alfalfa hay (49.63 vs. 52.24 and 0.06 vs. 0.11 for the treated and untreated samples, respectively). However, there was a negative significant effect (p<0.05) effect of BPEO on both b and c fractions when sugar beet pulp was considered (84.01 vs. 80.95 and 0.09 vs. 0.08 for the treated and untreated samples, respectively). The gas production parameters of barley grain did not alter when BPEO was applied. The most important finding of the present study is the different response of the feed samples evaluated when treated with BPEO.

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