Effects of oregano essential oil, cobalt and synergistic of both of them on rumen degradation rate and fermentation characteristics for corn silage

This study used oregano essential oil (EO), cobalt (Co) and synergistic of both of them additives instead of antibiotics to explore the effects of different additives on the corn silage fibre structure degradation, nutrient degradation rate and rumen fermentation characteristics of sheep. The additives used in the study as a product were provided by Ralco, Inc., USA. The Latin square experimental design was adopted with 5 treatments. The following treatments were fed through the rumen fistula: carrier (Car), carrier + EO, carrier + Co, carrier + EO + cobalt (EOC) and no additives as the control (CON). These treatments were fed to five sheep for five rounds at a dose of 80 mg/kg. At 48 h of degradation, the area of degraded corn leaf and husk reached 100%, SEM results showed that except for Car and CON treatment, there were obvious destroyed fibre structure differences under EO, Co and EOC treatment, showing total disappearance of leaf epidermal cells, palisade tissue and spongy tissue, especially under EOC. Under EOC treatment, DMD 48 h , CPD 48 h , NDFD 48 h and ADFD 48 h increased by 3.33%, 3.89%, 7.64% and 5.67%, respectively, compared with CON, while NDFD 48 h and ADFD 48 h increased by 4.70% and 6.05% under Co (p > 0.05). The NH 3 -N concentration in rumen fluid decreased by 19.36%, 27.20% and 19.48%, while the microbial protein (MCP) content increased by 6.32%, 4.29% and 5.97% (p > 0.05) under EO, Co and EOC treatments compared with CON at 48 h (p 0.05). Feeding EOC increased the fibre structure degradation and nutrient degradation rate of corn silage and improved rumen fermentation in sheep, resulting in better effects than feeding EO or Co alone. HIGHLIGHTS This article revealed the significance of oregano essential oil synergistic with cobalt (EOC) on rumen fermentation characteristics and nutrient degradation rate of sheep. In this study, the degradation of leaves in the rumen was observed by scanning electron microscopy, and the degradation area was calculated by electron microscopy for the first time. The results of this study will provide the theoretical basis for EOC as a substitute for antibiotics.