This experiment was conducted to study the effect of addition of 2 medicinal plants, peppermint or thyme, on digestibility of a finishing diet in lambs. Eighteen male lambs (initial body weight 21.6 ± 1.5 kg) were randomly assigned to one of 3 diets: control (with no additive), peppermint (control diet plus 3% of peppermint) or thyme (control diet plus 3% of thyme), for a 90-d finishing period. Lambs were fed individually and digestibility of nutrients were determined using insoluble ash method during 5 d of fecal sampling from all lambs. The ratio of concentrate:forage was 70:30. Diets were isocaloric and isonitrogenous. Data were analyzed as a completely randomized design with means compared using Duncan's test (SAS v9.2). Addition of peppermint or thyme to diets had no effect on digestibility of CP, ether extract, NDF and ADF but improved DM intake and digestibility of calcium and phosphorus (P < 0.05). Supplementation with peppermint or thyme could increase performance of finishing lambs through improved feed intake. Results are given in Table 1. Table 1. Effect of peppermint and thyme on DMI (g/d) and in vivo nutrient digestibility (%) of a finishing diet in lambs

Item	Peppermint	Thyme	Control	SEM	P-value
DM intake	1,494.4a	1,488.5a	1,185.5b	40.6	0.001
Nutrient digestibility
Crude protein	77.65	75.17	76.96	0.667	1.14
Ether extract	77.93	75.43	76.58	0.074	1.28
NDF	58.04	59.50	65.19	0.424	2.20
ADF	49.76	45.96	50.13	0.183	2.56
Calcium	53.98a	44.21a	37.30b	2.99	0.05
Phosphorus	66.65a	53.61a	50.66b	2.99	0.03