1916
Effects of Thyme Oil (Thymus Vulgaris) on in vitro Ruminal Fermentation Kinetics
The objective of the present study was to investigate the effects of dietary thyme oil (1.25, 2.50 and 3.75 ml/kg DM) or monensin (Rumensin®; 20 mg/kg DM) on ruminal in vitro gas production kinetics. Diets were formulated using the Small Ruminant Nutrition System to meet the requirements of growing sheep and were 80% Tifton hay (Cynodon sp.) and 20% concentrate DM. Homogenized samples of each diet (1.0 g) were placed into 160 ml serum bottles with 10 ml of rumen inoculum and 90 ml of a buffer solution. Rumen inoculum was collected from 4 fistulated male lambs before the first feed of the day was offered. Each lamb was fed one of the four diets, ad libitum. Six bottles were used per treatment and two additional bottles containing buffered medium, rumen fluid and the feed additives were used as background control. The volume of gas produced was indirectly measured at 2, 4, 6, 8, 10, 12, 15, 18, 21, 24, 36, 48, 72, and 96 h of incubation using the pressure reading technique. To estimate kinetic parameters of gas production data were fitted to the model Y = A {1- exp[-b(t-L) -c(√t-√L)]}, where Y = cumulative gas production (ml) at time t; A = the asymptotic gas production (ml); b and c = constant rates (h-1 and h-1/2, respectively); t = incubation time (h) and L = lag time (h). Thyme oil additive at 3.75 ml/kg resulted in similar gas production compared to monensin (194.1 ± 3.3; 197.2 ± 1.1 ml, respectively) and in reduced (P < 0.05) gas production compared to either 1.25 ml/kg (209.8 ± 0.9 ml) or 2.50 ml/kg (211.0 ± 0.5 ml) of thyme oil. The fractional degradation rate (FDR) was reduced (P < 0.05) in the 2.5 and 3.75 mg/ml thyme oil treatments (0.045 ± 0.0007 h) compared to treatment with monensin (0.049 ± 0.0003 h), while the 1.25 ml/kg treatment (0.047 ± 0.0003 h) did not differ from any other treatment. Lag time was reduced (P < 0.05) in the monensin (1.16 ± 0.03 h) compared to the 3.75 ml/kg thyme oil treatment (2.26 ± 0.17 h), however no difference was detected among monensin, 1.25 ml/kg (1.66 ± 0.16 h) and 2.50 ml/kg (1.24 ± 0.17 h) of thyme oil. In conclusion, thyme oil may be an effective alternative to monensin for manipulation of rumen fermentation.
Keywords: Thyme Oil, Rumen Gases, Sheep