Different medicinal plants have been used in animal and poultry nutrition in last decade. It seems that there are some potential to these medicinal plants to replace with common antibiotics. Licorice root (Glycyrrhiza glabra) is a medicinal plant that extensively was used in different studies. In the present study, the effect of dietary addition of licorice root on performance and blood energy indicator concentrations (glucose, non-esterified fatty acid (NEFA), beta hydroxyl butyrate (BHB) and immune responses parameters (total immunoglobulin (IG), IgG and IgA) was evaluated on female Holstein calves. The fourteen female Holstein calves with average body weight of 85.5 kg were subjected to two different treatments (seven animals per each treatment) in a completely randomized design. The control treatment was considered as C and supplemented treatment with licorice was considered as L. The study lasted ten weeks. Of which the first week was considered as adaptation period. Feed intake was measured daily and blood sample were collected twice throughout the experiment. The results show that average dry matter intake (DMI) was 1790 and 1860 g/d for treatments C and L, respectively (P>0.05). The NEFA was different significantly between treatments (P<0.05). The IgA concentration was not differed between treatments; however both total Ig and IgG concentrations were positively increased by licorice supplementation treatments (P<0.05). Total Ig concentration was 105.1 and 138.2 mg/dL for treatments C and L, respectively which shows that licorice addition caused to 31% increase in immunity responses compared to control treatment. In conclusion the results show that although licorice supplementation did not affect performance of animal, but it has potential to improve energy status in dairy calves' nutrition and also increased immune response of animal.
