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

• Essential oils blend (EOB) had very high radical scavenging activity.
• Average daily weight gain of calves was increased using herbal supplements.
• Calves fed essential oils blend had higher blood insulin at abrupt weaning time.
• Results showed that EOB had potential to suppress the stress in suckling calves.

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<0.05). Supplementation of the starter diets with essential oils and/or distillation residues increased (P<0.05) feed intake and average daily weight gain of calves. These calves had about 3 d lower age (P<0.05) and higher body weight (BW) at the weaning time. Calves fed EOB had higher (P<0.05) insulin concentrations during the weaning period, especially in abrupt weaned group compared to the group CON-A. The weaning method and treatment had no effect on total serum protein (TSP), serum albumin and globulin. It is concluded that supplementation of starter diets with a mixture of essential oils or distillation residues had a beneficial effect on the growing performance of suckling calves and may change some of blood metabolites.