Abstract
Simple SummaryIn the context of a shortage of feed resources and a complete ban on veterinary antibiotics, searching for green additives that can improve the production performance of ruminants has become a popular research topic. Oregano essential oil (EO) inhibits rumen gas production (GP) and regulates animal digestive metabolism, and cobalt lactate (Co) can improve feed digestibility. However, previous studies on EO of oregano and Co showed different results. Therefore, the present study aimed to investigate the effects of different EOC addition levels on rumen in vitro fermentation and rumen bacterial community composition, and the experimental data obtained showed that all five EOC (0.1425% cobalt lactate + 1.13% oregano essential oil + 98.7275% carrier) addition levels in this experiment had no significant effect on nutrient digestibility. However, the addition of 1500 mg·L−1 EOC significantly improved rumen fermentation parameters and altered the microbiota composition. All presented data provide a theoretical basis for the application of oregano essential oil and cobalt in ruminant nutrition.The objective of this experiment was to evaluate the effect of different EOC (0.1425% cobalt lactate + 1.13% oregano essential oil + 98.7275% carrier) levels on in vitro rumen fermentation and microbial changes. Six EOC levels (treatments: 0 mg·L−1, CON; 50 mg·L−1, EOC1; 100 mg·L−1, EOC2; 400 mg·L−1, EOC3; 800 mg·L−1, EOC4 and 1500 mg·L−1, EOC5) were selected to be used to in vitro incubation. The in vitro dry matter digestibility (IVDMD), in vitro neutral detergent fiber digestibility (IVNDFD), in vitro acid detergent fiber digestibility (IVNDFD), pH, ammonia-nitrogen (NH3-N) concentration, total volatile fatty acid (TVFA) concentration and microbial protein (MCP) concentration were measured after 48 h incubation, after which the groups with significant nutrient digestibility and fermentation parameters were subjected to 16S rRNA sequencing. The results showed that the total gas production (GP) of the EOC5 group was higher than that of the other groups after 12 h of in vitro incubation. TVFA, NH3-N and MCP concentrations were also shown to be higher in group EOC5 than those in other groups (p < 0.05), while NH3-N and MCP concentrations in the EOC2 group were lower than those in other groups significantly (p < 0.05). The molar ratio of acetic acid decreased while the molar ratio of propionic acid increased after the addition of EOC. 16S rRNA sequencing revealed that the rumen microbiota was altered in response to adding EOC, especially for the EOC5 treatment, with firmicutes shown to be the most abundant (43.1%). The relative abundance of Rikenellaceae_RC9_gut_group was significantly lower, while the relative abundance of uncultured_bacterium_f_Muribaculaceae and Succiniclasticum was significantly higher in the EOC5 group than those in other groups (p < 0.05). Comprehensive analysis showed that EOC (1500 mg·L−1) could significantly increase gas production, alter sheep rumen fermentation parameters and microbiota composition.
Highlights
The exploitation and utilization of straw feed has always been an important subject in animal nutrition, as massive burning leads to serious waste of crop straw, it is difficult to apply to monogastric animals [1]
Previous studies had shown different effects of oregano essential oil and cobalt on rumen microbial activity and fermentation characteristics in ruminants due to different additive types and adding levels [16], which may be related to the type of EO, its structure and the substrate employed
To develop new additives for EO binding to effectively regulate ruminant production, in this study, the effects of different gradients of oregano essential oil and cobalt lactate binding on nutrient digestibility, rumen fermentation patterns and microbiota were evaluated by in vitro incubation
Summary
The exploitation and utilization of straw feed has always been an important subject in animal nutrition, as massive burning leads to serious waste of crop straw, it is difficult to apply to monogastric animals [1]. The rumen microbial community is very stable throughout the life cycle of animals, the diversity of the microbial community is largely influenced by diet (e.g., different feed types and additives) [3]. Some studies have concluded that supplementing feed with additives such as probiotics has a positive effect on the gastrointestinal microbiota of cattle [4]. The rational use of feed additives to improve the gastrointestinal flora of ruminants is highly important for improving the utilization of feed resources. The use of antibiotics in animal feed has been almost banned in the European Union since 2006 [5]. China’s Ministry of Agriculture and Rural Affairs issued Announcement No 194 in 2020, which completely banned the addition of antibiotics to feed
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