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Beyond the spice rack: Oregano and calves

Amanda Kerr and Lauren Yanch for Progressive Dairy Published on 10 September 2021

The use of plants in human medicine has a long, rich history. With increasing demand for maximized animal production outputs per consumable resource, the use of plant compounds in animal feed can complement good management practices to optimize health and feed efficiency.

Oregano mode of action 

The noteworthy medicinal properties of oregano relative to other medicinal plants is largely due to abundant presence of carvacrol and thymol, two potent compounds that can effectively combat gram-negative and gram-positive bacteria. Carvacrol and thymol have the ability to compromise bacterial enzymatic function, thereby influencing mechanistic pathways needed for survival such as energy metabolism. To elaborate further, carvacrol and thymol are able to impair cell wall integrity by rupturing the cytoplasmic membrane due to their phenolic composition. As a result, phospholipid membrane structure and stability are compromised, ultimately leading to bacterial cell death.



Oregano has been discovered to have very high oxygen radical absorbance capacity (ORAC) levels, meaning there is an ability to act as a protective agent toward enterocytes against reactive oxygen species that are released as a result of an immunological response. The addition of oregano in feed can serve immunological benefits, given that bacteria first encounter the immune system of the gastrointestinal tract (GIT). This therefore allows carvacrol and thymol’s potent mode of action to not only stop bacterial colonization at the source, but also to actively prevent dysbiosis – a reduction in microbial diversity – as essential oils favour gut stability and microflora homeostasis. Immune cells in the GIT are constantly sensing and surveying the gut for potential harm, and if found, an inflammatory immune response is generated, and if not kept in check, can lead to dysbiosis in the gut, reducing feed efficiency among others. Using oregano oil, a healthier population of gut microflora may be maintained and indirectly improve animal metrics. 

In vitro results

Conducting in vitro research can allow scientists to determine how well certain types of bioactive compounds, such as those found in oregano, limit specific pathogens. Although these results are not directly transferable to what will happen in an animal, it still provides insight to the effectiveness of essential oil compounds and products. A minimum inhibitory concentration (MIC) test is used to determine the amount of active ingredient needed to obstruct the growth of bacterial culture being grown. The lower concentration required to inhibit growth represents a stronger compound, as illustrated in Figure 1

oils versus bacteria

Individual compounds found within an essential oil exert different levels of inhibition if the bacteria has a cell wall (gram positive) or does not (gram negative). For example, the main compound within oregano oil, carvacrol, has a strong inhibition against gram-negative bacteria such as E. coli, and thymol, also found in oregano oil, is more specific to inhibit gram-positive bacteria such as Staphylococcus aureus

Effects of oregano on young animal performance and growth 

Incorporating oregano into animal feed has received an abundance of attention across multiple species and production types. Regarding the use in young animals, feed efficiency and improved recovery time from intestinal illness have been some of the reported benefits. As an example, one study reported a reduction in scour severity and days with diarrhea when calves received oregano oil through the milk replacer.


In addition, oregano inclusion has also been shown to be appetite stimulating and suggested to be a catalyst for the onset of rumen development. Additional research has confirmed oregano’s persistency against gram-negative bacteria and mentions oregano as an anti-cryptosporidial. Through directly impairing pathogenic, and potentially pathogenic bacterial growth, and indirectly supporting a stable and balanced GIT microbiome, oregano oil may serve a benefit to young animals. However, the quality, consistency and purity of the source of oregano oil is essential to maximizing benefits. 

Nevertheless, there is no one solution to raising healthy and strong youngstock due to the vast influences and interactions of genetics, environment and management. With proper and concentrated attention played to critical details of young animal health and well-being, additives such as prebiotics, probiotics, acidifiers and essential oils may be beneficial to support a healthy gut environment. These additives, including oregano oil, can be found in some milk replacer formulas.  end mark

References omitted but are available upon request. Click here to email an editor.

Amanda Kerr is a nutritionist with Grober Nutrition Inc. Lauren Yanch is a technical and operations specialist for Grober Nutrition Inc.