Trial Summary - The Effect of Orego-Stim® on Antimicrobial Resistance in Calves


  • Antimicrobial resistance (AMR) is a serious, global issue affecting all classes of livestock and humans alike, especially 3rd and 4th generation cephalosporins that are listed as “Highest Priority Critically Important Antimicrobials” (WHO, 2017)’.
  • Orego-Stim® Liquid, when included in milk at 10ml per calf per day for 10 days, significantly reduced development of AMR in E. coli to 4th generation cephalosporins in the faeces of dairy calves.


  • The milk from dairy cows that have been treated with antibiotics for mastitis cannot be sold for human consumption (waste/dump milk) and is usually fed to calves on the farm.
  • This practice is known to be a risk for transfer of AMR to the calves and is a concern for global calf production and human health (EFSA, 2017).

  • Orego-Stim® is a high quality eubiotic containing 100% natural oregano oil.


A pilot study was carried out at the University of Reading in the UK. 10 male Holstein dairy calves were assigned to one of two treatments at 2 days of age; Control with no supplements in the milk, Orego-Stim with 10ml/calf/day of Orego-Stim® Liquid added to the milk. The milk used was unsaleable, waste milk from the University dairy herd. Orego-Stim® was included in both the morning and evening feeding (5ml in 2.5 litres milk) for the first 10 days only. All calves then received the same milk and concentrates until weaning at day 60. Calves were individually housed until 21 days of age then housed together in a straw pen until the end of the trial at day 78. Faecal samples were taken on days 0, 3, 7, 10, 14, 21, 56 and 70 for analysis of E. coli and Enterococci spp. as well as to determine the degree of AMR to 5 different antibiotics on the Critically Important Antimicrobials list.


Faecel Scores in Calves

Fig 1. Effect of Orego-Stim® on E. coli resistance to 4th generation cephalosporins in dairy calves (adapted from Ray et al., 2019, unpublished).

  • Calves offered 10ml Orego-Stim for 10 days had a highly significant reduction in the proportion of E. coli resistant to 4th generation cephalosporins (12.6% vs 44.1%, p<0.001).
  • This effect was maintained even after Orego-Stim supplementation had stopped.
  • The emergence of this resistance was delayed from day 3 (Control) to day 7 (Orego-Stim).

Orego-Stim | Help Improve Growth Performance in Dairy Calves


Orego-Stim is Anpario's 100% natural high quality oregano essential oil (OEO) additive range. 


  • OEO naturally contains antimicrobial and antioxidant compounds to support a healthy digestive system and aid nutrient absorption.
  • Supports animal's natural defence mechanism and aids natural immunity. 


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