Dose-Response Effects of Various Rumen Microbial Modifier Essential Oils on Protein Degradation Using <i>in vitro</i> Gas Production Technique

Abstract

The aim of this study was to investigate the effects of various doses of essential oils (EO) of thyme (TEO) or cinnamon (CEO) on <em>in vitro</em> rumen degradation of protein of a commercial total mixed ratio (TMR) containing 16.4% crud protein (CP). Treatments were TMR without any of EOs (control); control plus 25 µL of TEO (TEO25); control plus 50 µL of TEO (TEO50); control plus 25 µL of CEO (CEO25) and control plus 50 µL of CEO (CEO50). Rumen fluid was collected before the morning feeding from two rumen fistulated dairy cows. Approximately, 90 mL of buffered rumen fluid (BRF), 400 mg of feed sample plus carbohydrates (maltose, xylose and starch) at four concentrations (100, 200, 300 and 400 mg) were added to screw-cap bottles. Gas production (mL) and ammonia nitrogen concentration (mg) in each bottle were measured at 4, 8, 12, 24 and 30 h post-incubation and <em>in vitro</em> crude protein degradation (IVDP) was calculated via a linear regression. Both TEO and CEO caused a significant reduction in IVDP values compared with those of control (P<0.05). The IVDP values for treatments of control, TEO50 and CEO50 after 30 h post incubation were 0.56, 0.33 and 0.48, respectively. Amount of the readily fermentable fraction and the potentially degradable fraction of the feed protein were affected significantly by treatments (P<0.05). Also, the effective crude protein degradability (EPD) was significantly affected by the EOs (P<0.05). These results suggest that the TEO and CEO might be used for manipulating the ruminal protein degradability.