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, Staphylococcus 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.  The tested essential oils had very good antibacterial properties against pathogens isolated form mammary glands of cows with clinical mastitis.  Based on literature/web searches that provided information that essential oils in in vitro and in vivo are very tissue irritant and caused up to a 100-fold increase in somatic cell counts and bloody milk.  Hence, we terminated attempts to assess the safety of intra-mammary infusions of essential oils.

Objectives/Performance Targets

The objectives of this project are to:

To determine the minimum inhibitory concentration (MIC) of Manuka honey and guava leaf extract to bacteria commonly associated with bovine mastitis. 

To establish in-animal safety of candidate formulations and in-milk inhibition metabolites residue depletion

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.

Based on others’ research, most essential oils are very tissue irritant and cannot be safely infused into udders at concentrations needed to achieve the MIC of mastitis pathogens.  We, hence, had to abandon the safety studies of mammary infusion of essential oils into the quarters of lactating cows.

Accomplishments/Milestones

In 2015 we geared up to assess the safety of mammary infusion of essential oils on mammary epithelium before essential oils are injected into mammary quarters of cows.  Assuming the concentration of essential oils needed in the udder needed to be at least the MICs determined previously, we determine the amount of antimicrobial drugs to inject into a mammary quarter will have to be a 50%-100% concentration of the essential oils.  Such concentrations may be too irritating to the mammary epithelium.  We initiated a web and literature search for safety and tissue reactivity/irritation of essential oils.  Most essential oils are very tissue irritant.  In a yearly report from a USDA, NIFA grant entitled: “Investigating the potential of natural antimicrobials for controlling bovine mastitis”, it was reported that infusion of trans-cinnamaldehyde at concentrations of 10%, 20, and 30% increased signs of discomfort (tail flicking and kicking) in the cows as well as a 100-fold increase in somatic cells counts and blood in the milk.  Based on the findings reported in the grant report we terminated the 2^nd objective of testing safety of the essential oils when injected into mammary glands at concentration we calculated to be needed to achieve concentrations above the mastitis organisms’ MIC.   The next steps for us would be determine if essential oils can be manipulated to reduce their tissue irritant properties, however because of the switch in focus from Manuka honey to essential oils we did not have time to initiate this research within the time frame of the grant.

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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