Effect of essential oils and distillation residues blends on growth performance and blood metabolites of Holstein calves weaned gradually or abruptly

The objective of this study was to investigate preweaning calf performance responses and initial postweaning profile of some blood metabolites to dietary supplementation of calf starter with essential oils or distillated residues blend ( Rosmarinus officinalis L., Zataria multiflora Boiss, and Mentha pulegium L.). Sixty Holstein calves, were randomly assigned to three dietary treatment groups: (1) starter with no additive (CON), (2) starter with essential oils blend (EOB, 300 mg/kg starter), and (3) starter with distillation residues blend (DRB, 50 g/kg starter). The blend was prepared by mixing the essential oils or the distillation residues (1:1:1) and then was added to the starter diet. Each group of calves was weaned based on two different methods: (1) gradual weaning during 4 d [G], and (2) abrupt weaning [A]. Results of DPPH test showed that radical scavenging activity of EOB was higher than DRB (81.4 vs. 15.4%) ( P P P P