Effects of Oregano (Origanum vulgare) and Thyme (Thymus vulgaris) Oils on Growth Performance and Blood Parameters in Holstein Suckling Calves

This experiment was conducted to compare the effect of supplementation of milk with thyme (THY) and oregano (ORE) essences separately or a mixture of THY and ORE essences on growth performance, hae-matological parameters and some blood metabolites of Holstein suckling calves. Forty-eight Holstein calves (48.31±5.82 kg) were randomly allocated to four treatments including (1) control without essential oil sup-plement; (2) THY oil mixed in milk at 5 mL/d/calf; (3) ORE oil mixed in milk at 5 mL/d/calf; (4) 2.5 mL THY oil + 2.5 mL/d/calf ORE oil mixed in milk (TOM). According to the results, the experimental diets had no significant effect on body weight, average daily gain, and feed conversion rate in the entire experi-ment (P>0.05), although the parameters of starter and total feed intake were increased (P<0.0001) in the ORE and TOM groups. Values of packed cell volume, haemoglobin, mean corpuscular volume, and lym-phocyte percentage were increased (P<0.05) in the ORE group compared with the control. Also, our results demonstrate the supplementation of either oregano or thyme essential oils increased (P<0.05) serum iron concentration, alanine aminotransferase, and aspartate transaminase activities. Concentrations of total cho-lesterol and total triglyceride were decreased (P<0.05) in calves given both oils compared to the control group. Further confirmation of these results is warranted, and more research is needed to identify and clearly explain in the contribution of oregano or thyme oils (individual or mixtures); however our results suggested that oregano oil might be more useful as the promising feed additive for suckling calves nutrition.