Effect of supplementation of calf starter with licorice root powder on growth performance, blood metabolites and fermentation characteristics in Holstein dairy calves

The objective of this study was to investigate the pre-weaning calf performance, weaning age and rumen fermentation responses to dietary supplementation of the calf starter with different levels of licorice root powder (LRP). The experiment was conducted with 3 treatments and 12 replicates as a completely randomized design. Thirty-six Holstein calves (birth weight 40 ± 0.5 kg) were randomly assigned to three dietary treatments: (1) starter with no additive (control), (2) starter diet with 2.5 % of LRP, and (3) starter diet with 5 % LRP. Supplementation of the starter diets with LRP linearly increased the dry matter intake (DMI) and average daily weight gain of the calves, and reduced weaning age compared to the control (P < 0.05). There was no significant effect on rumen pH but ruminal NH₃N concentration was linearly lower in calves fed with LRP than the control group (P < 0.05). Concentrations of total volatile fatty acids (VFA), acetic acid and butyric acid were not affected by LRP supplementation. The concentration of propionic acid in calves fed with 5 % level of LRP was significantly higher than the control group but the ratio of acetic acid to propionic acid was significantly lower in the calves that received LRP in their starter feed and these changes followed a linear trend (P < 0.05). Calves that were fed with 5 % LRP recorded linearly higher glucose concentrations than the control group and those receiving 2.5 % LRP (P < 0.05). The treatments did not affect total serum protein (TSP), serum albumin and triglycerides. Calves feeding on the 5 % LRP diet recorded lower blood urea nitrogen (BUN) levels than the control group as linear trend (P < 0.05). It was concluded that supplementing the starter diet with licorice root powder can beneficially affect growth performance and enhance rumen fermentation in suckling calves.