Table 2.

Dose–response effect of eucalyptus oil (EUC) and anise oil (ANI) on in vitro gas production (GP), DM digestibility (DMD), and rumen fermentation characteristics after 24 h of incubation

Items		Treatment,1 mg/L					SEM	P value
		0	50	100	200	400		L2	Q2
GP, mL	EUC	51.6	46.2	56.4	53.5	49.0	3.40	0.82	0.26
	ANI	51.6	53.2	50.6	46.3	40.9	1.44	<0.01	0.74
DMD, %	EUC	21.3	19.6	19.7	19.5	15.8	0.54	<0.01	0.32
	ANI	21.3	17.7	17.9	15.9	13.0	0.54	<0.01	0.04
CH4, mL	EUC	11.1	11.8	12.6	11.0	9.1	0.62	<0.01	0.08
	ANI	11.1	10.7	10.5	8.1	5.8	0.50	<0.01	1.00
CH4, % of GP	EUC	21.6	22.5	22.3	20.6	18.6	1.01	0.02	0.46
	ANI	21.6	20.2	20.8	17.6	14.1	1.07	<0.01	0.86
CH4, mL/g of digestible DM	EUC	261	302	320	283	288	15.7	0.87	0.19
	ANI	261	303	295	255	222	14.8	<0.01	0.17
pH	EUC	6.71	6.69	6.74	6.71	6.68	0.032	0.51	0.56
	ANI	6.71	6.61	6.62	6.66	6.59	0.024	0.03	0.67
NH3-N, mM	EUC	27.7	25.2	23.5	26.0	37.3	5.37	0.03	0.10
	ANI	27.7	27.9	26.7	23.2	14.9	4.68	<0.01	0.43
Total VFA, mM	EUC	77.7	87.9	84.5	86.5	80.7	5.54	0.92	0.27
	ANI	77.7	67.5	72.3	61.6	58.2	2.46	<0.01	0.13
Molar proportion, mM/100 mM
Acetate	EUC	67.0	67.0	67.3	67.4	65.5	0.60	0.08	0.15
	ANI	67.0	66.7	66.2	65.8	69.8	0.43	<0.01	<0.01
Propionate	EUC	16.7	16.4	16.4	16.4	22.7	0.40	<0.01	<0.01
	ANI	16.7	17.1	17.5	20.5	17.9	0.35	<0.01	<0.01
Butyrate	EUC	14.1	14.5	14.2	13.6	10.2	0.31	<0.01	<0.01
	ANI	14.1	14.1	14.1	12.0	11.0	0.226	<0.01	0.58
Isobutyrate	EUC	0.57	0.58	0.56	0.51	0.24	0.044	<0.01	0.06
	ANI	0.57	0.55	0.56	0.33	0.22	0.032	<0.01	0.69
Valerate	EUC	0.48	0.48	0.48	0.49	0.53	0.016	0.05	0.31
	ANI	0.48	0.45	0.49	0.53	0.50	0.019	0.13	0.28
Isovalerate	EUC	1.11	1.14	1.05	1.05	0.78	0.053	<0.01	0.18
	ANI	1.11	1.10	1.14	0.87	0.54	0.031	<0.01	0.02
Acetate:propionate	EUC	4.01	4.10	4.10	3.97	2.89	0.101	<0.01	<0.01
	ANI	4.01	3.91	3.79	3.21	3.90	0.089	0.13	<0.01

¹The 0.5 mL EUC and ANI mixture (EUC and ANI dissolved in ethanol with different proportion) were added to 30 mL of medium respectively to up to 0, 50, 100, 200, and 400 mg/L of incubation media as five treatments.

²L, Q = linear or quadratic effect of different EUC and ANI addition concentration (0, 50, 100, 200, and 400 mg/L of incubation media).