Non-Antibiotic Alternatives for Bovine Mastitis Therapy

Non-Antibiotic Alternatives for Bovine Mastitis Therapy

Summary

This project aims to develop intra-mammary, non-antibiotic alternatives to treating mastitis in dairy cows raised under organic and conventional production methods.  In 2013, we determined the minimum inhibitory concentrations (MICs) of Manuka honey for E. coli and Streptococcus isolated from cows with clinical mastitis.  The MICs obtained with Manuka honey were very likely too high to be able to achieve needed concentrations of honey in the quarters of cows with clinical mastitis.  Hence, we redirected our efforts to involve essential oils from plants that have been shown to have very good antibacterial properties. 

In 2014, we determined the MICs of 88 clinical mastitis isolates to the essential oils: oregano oil, trans-cinnamonaldehyde, carvacrol and thymol.  The MICs for essential oils ranged between ≤0.003906% (vol/vol) and >1% (vol/vol).  The lowest MICs were seen for TC.  MICs varied for E. coli, Staphylococcus spp. and Streptococcus spp.  In general MICs were lowest in the order: trans-cinnamaldehyde<carvacrol<thymol<oregano

Objectives/Performance Targets

The objectives of this project are to:

1. To determine the minimum inhibitory concentration (MIC) of Manuka honey and guava leaf extract to bacteria commonly associated with bovine mastitis.
2. To establish in-animal safety of candidate formulations and in-milk inhibition metabolites residue depletion
3. To determine cure rate of mild to moderate clinical mastitis in dairy cows using candidate formulations

Work towards completing Objective 1 was performed during 2014.  The first objective of this NCR-SARE project was to assess the in-vitro effect of Manuka Honey and Guava Extract to inhibit the growth of common mastitis pathogens isolated from dairy cows with clinical mastitis.  To accomplish that goal, we proposed to determine the minimum inhibitory concentrations (MIC) of Manuka Honey and Guava Extract for bacteria causing clinical mastitis in dairy cows.  We were not able to identify a source of Guava extract that was consistent in quality and quantity.   The MICs obtained for Manuka honey ~6-8% (weight/volume) are likely so high that we would not be able to obtain high enough concentrations of the honey in the udder of dairy cows to reach the MIC  needed.

To compensate for the loss of Guava extract and Manuka honey as viable options for treatment of mastitis, we identified several essential oils that appeared to have much lower MICs than Manuka honey.  These oils include: oregano oil, two constituents of oregano oil; carvacrol and thymol, and trans-cinnamaldehyde.

We determined the MICs to the following essential oils: oregano oil, carvacrol, thymol and trans-cinnamaldehyde.

Accomplishments/Milestones

We determined the MICs for oregano oil, carvacrol, thymol and trans-cinnamaldehyde to 33 E. coli, 27 Staphylococcus spp. and 28 Streptococcus isolates, respectively.  We also determined the MICs of these isolates to the antimicrobial drugs ampicillin and ceftiofur, respectively.  For the two antibiotics (ampicillin and ceftiofur) the log2 dilutions tested ranged from 0.0625 to 64, and for the essential oils the log2 dilutions ranged from 0.003906% (vol/vol) to 1% (vol/vol).

For the 33 E. coli isolates, the MICs ranged from 2 to >64 for ampicillin, ≤0.0626 to 16 for ceftiofur, 0.0125 to >1 for oregano, 0.0625 to 1 for carvacrol, 0.0625 to >1 for thymol, and 0.03125 to 0.0625 for trans-cinnamaldehyde, respectively.

For the 27 Stapylococcus isolates, the MICs ranged from ≤0.0625 to >64 for ampicillin, ≤0.0626 to 16 for ceftiofur, 0.015625 to >1 for oregano, 0.015625 to >1 for carvacrol, 0.015625 to >1 for thymol, and ≤0.003906 to 0.0625 for trans-cinnamaldehyde, respectively.

For the 28 Streptococcus isolates, the MICs ranged from ≤0.0625 to 0.25 for ampicillin, MICs to ceftiofur was not done for streprococcal isolates, 0.5 to >1 for oregano, 0.015625 to 0.0625 for carvacrol, 0.03125 to 0.0625 for thymol, and 0.015625 to 0.0625 for trans-cinnamaldehyde, respectively.

For the E. coli isolates, the MIC₅₀ and MIC ₉₀ for the essential oils were 0.5 and >1 for oregano, 0.125 and 0.125 for carvacrol, 0.125 and 1 for thymol and 0.03125 and 0.03125 for trans-cinnamaldehyde, respectively.

For the Stapylococcus isolates, the MIC₅₀ and MIC ₉₀ for the essential oils were 0.5 and >1 for oregano, 0.125 and 0. 5 for carvacrol, 0.0625 and 0.25 for thymol and 0.03125 and 0.0625 for trans-cinnamaldehyde, respectively.

For the Streptococcus isolates, the MIC₅₀ and MIC ₉₀ for the essential oils were 1 and >1 for oregano, 0.03125 and 0.0625 for carvacrol, 0.03125 and 0.03125 for thymol and 0.0625 and 0.0625 for trans-cinnamaldehyde, respectively.

As expected the median MICs for essential oils were much lower – almost by a factor 100 – than for Manuka honey.  Hence, essential oils may be better targets for alternatives to antimicrobial drugs for treatment of mastitis in cattle. 

The next step is to assess the safety of essential oils in respect to mammary epithelium before essential oils are injected into mammary quarters of cows.  If we used the methodology to determine the amount of antimicrobial drugs to inject into a mammary quarter, we will have to inject a 50%-100% concentration of the essential oils.  Such concentrations may be too irritating to the mammary epithelium.  However, it may be that essential oils may be needed in lesser concentration in the mammary gland, because preliminary studies in cell cultures suggest that essential oils may adhere to mammary epithelium.

Impacts and Contributions/Outcomes

Mastitis is the most common health condition requiring management on both conventional and organic dairy farms.  The cost of each case of mastitis on a dairy averages $155.08 per each episode and is estimated to cost the entire US Dairy industry $1.7 – 2 billion each year.  Vaccinations to reduce the occurrence and/or severity of mastitis, adequate hygiene throughout milking procedures and sanitation in cow housing are effective control methods common to both organic and conventional dairy farms.  Conventional dairies commonly rely on antibiotics to prevent new cases of mastitis during the cow’s non-lactating (dry) period and to treat clinical cases of mastitis during lactation, however antibiotics are not allowed for use in organic dairies under the US National Organic Program.  Both organic and conventional dairy producers would benefit from the development of new non-antimicrobial alternatives to bacterial infections in livestock.  These reasons are based on the intense scrutiny of antimicrobial drug use in animal agriculture because of antimicrobial resistance issues, a decrease in market incentives for developing new antimicrobial drugs, and the growing antibiotic-free segment of the dairy industry.  Hence, developing the described non-antibiotic alternatives to mastitis treatment in dairy cows may increase the sustainability of the dairy industry.  During this year we did not participate in outreach activities

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