The Effect of Monensin, Thyme and Cinnamon Essential Oils on Nutrient Digestibility, Ruminal Dry Matter and Crud Protein Degradability of Some Feedstuff and Plasma Metabolites in Holstein Steers

The objective of this research was to evaluate the effects of monensin (MON), thyme (THY) and cinnamon (CIN) essential oils on dry matter and crud protein degradability characteristics of cottonseed meal, barley grain and corn silage, nutrient digestibility, and some plasma metabolites in Holstein steers (540 ± 35 kg initial BW) fed high-concentrate diets. Four rumen fistulated Holstein steers were used in a 4×4 Latin square design with 21-d periods and 4 treatments: control (no additive), THY (thyme oil; 500 mg/kg DM), CIN (cinnamon oil; 500 mg/kg DM) and MO (monensin; 33 mg/kg DM). Steers were fed ad libitum a basal diet as TMR consisting of 30 percent forage and 70 percent concentrate. Apparent digestibilities of dry matter, crud protein, and acid detergent fiber were similar among treatments, except neutral detergent fiber (NDF) digestibility which was lower (P ≤ 0.05) in steers fed CIN compared to those fed the MON diet. The addition of essential oils (EO) and MON had no effect on DM degradability parameters of cottonseed meal, barley grain and corn silage. Crud protein degradability characteristics of barley grain and corn silage were not influenced by additive treatments. Similarly, supplementation with EO and MO had no effect on the NDF degradability of corn silage. For CP degradability of cottonseed meal, except rapidly degradable fraction (a) and effective rumen degradability of CP, which was similar among experimental treatments; Feeding EO decreased (P ≤ 0.05) the slowly degradable fraction (b) of CP. The degradation rate of CP (c) was significantly higher (P ≤ 0.05) with than without MON. Plasma concentrations of glucose, urea nitrogen and cholesterol were not affected by MON, THY or CIN supplementation; although Plasma concentration of triglyceride was significantly increased by adding CIN compared to MON and THY (P ≤ 0.05). Results of this research indicate that supplementing steers with THY and CIN (500 mg/kg DM) had limited effects on nutrient digestibility, rumen dry matter and crud protein degradation characteristics of feedstuff and plasma metabolite consentrations.