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Milk Quality Laboratory


Prototheca (algae) under the microscope.

Valleywide Veterinary Services now has a full service milk quality laboratory designed to evaluate individual cow samples and pooled bulk tank samples for the presence of pathogenic, mastitis causing bacteria; using National Mastitis Council protocols. We read our aerobic cultures at 24 and 48 hours in order to identify all environmental and contagious organisms. Our Mycoplasma cultures are read at 5 and 7 days.

We work closely with the Cornell University Quality Milk Production Services (QMPS) for advanced microbiological investigation on unknown or unusual bacteria for quality control.

Our samples are cataloged in our milk laboratory computer program that generates easy-to-read reports. This will aid clients in monitoring the progress of their milk quality program and provides a searchable database that can be used for benchmarking.

All samples are evaluated and recorded by a licensed veterinarian. Consultation is available to assist in the development of a milk quality program aimed at meeting each client’s needs and goals.

Please talk with you veterinarian if you are interested in using our milk lab service.

Milk Quality Laboratory Culturing Overview


Our lab takes your milk samples and inoculates media that contains nutrients required for bacterial growth. The inoculated media is then placed in an incubator that contains the appropriate atmosphere and temperature to encourage growth of the target organisms.


Most common mastitis causing bacteria will grow on standard Blood agar media. Blood agar plates once incubated will be looked at and findings recorded at 24 hours and 48 hours. Identification of bacteria is made based on visual characteristics of the colonies and the result of additional laboratory tests. For instance, Staphylococcus aureus is usually differentiated from other staphylococci based on a positive coagulase reaction along with other typical characteristics.


Another additional test that comes standard at our lab is use of MacConkey agar to facilitate the identification of Gram-negative (coliforms) bacteria, such as E.Coli and Klebsiella. Both the coagulase reaction test for Staph aureus and plating on MacConkey agar take an additional 24 hours for results. Other biochemical tests are required for identification of bacteria at the species level.


The Incubator


Identification of Mycoplasma spp. requires the use of media containing specific nutrients not found in general medias and incubation in a CO2 enhanced environment. Mycoplasma plates must be incubated for a total of seven days and are read at both five and seven days.


Prototheca, as well as yeast, does grow on blood agar and we routinely screen for both. However, selective Prototheca isolation/enrichment media (PIM, PEM) can be used to enhance recovery from environmental sources and from milk. For this reason we have added PIM plates to all bulk tank samples, but they are also available for individual cow samples upon request.

We thank you for your business!

Milk Lab

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