Diagnosing Mastitis by Milk Culture - Commonly Asked Questions
Published: January 1, 2002
By: Ann Godkin - Veterinarian/OMAF
Introduction
This winter OMAF vets, Raw Milk Quality staff and Livestock Advisors conducted 20 workshops about mastitis for producers. Collecting milk samples to identify mastitis-causing bacteria in cow milk samples was a topic discussed and emphasized. During these sessions many questions arose and were discussed concerning when and how to collect the necessary milk samples.
When visiting farms and collecting samples for Ontario DHI, you may be (or may already have been) asked the following questions. I'm providing some answers to help you with this and to clear up some misconceptions producers seem to have. I welcome your comments and questions.
Can DHI samples be used for bacterial culture?
No. DHI samples cannot be used for mastitis culture because they have a preservative added. This prevents bacterial growth which is needed for mastitis bacteria identification in the lab. Also, samples for culture must be kept refrigerated or frozen between collection and arrival at the lab.
Can samples for bacterial culture be collected from the meters like DHI SCC and composition samples?
No. Although the meters and milking equipment are routinely cleaned and sanitized some bacteria may be added to the milk in passage. This is not enough to cause milk quality problems such as elevated plate loop counts (PLCs). However, if these bacteria are in the samples collected from the meters and grow on the cultures at the mastitis diagnostic lab it is impossible to determine whether the bacteria came from a mastitis infection in the cow or from the milking equipment. Additionally, these equipment bacteria multiply rapidly and can "overgrow" or hide mastitis bacteria so that they cannot be identified by the lab technician.
Is the culturing done in the same lab as the SCC testing?
No. Individual cow SCC testing is done at DHI in Guelph. Individual cow cultures are done by the labs that used to be part of OMAF but, as of April 1st, 1997, are part of the University of Guelph. There are two labs doing mastitis culture, one in Kemptville and one in Guelph. Some veterinary practises also offer this service on a limited basis.
If more than 10 samples are to be submitted to the veterinary diagnostic lab for culture the producer, or the producer's veterinarian, must contact the lab in advance to book a date.
How do I collect milk samples for SCC testing when the meters are not being used? (this situation arises when producers enrol in the 4 SCC tests but are not on routine production testing).
The best way to obtain consistent and interpretable SCC results is clearly to use meters to collect the milk samples. Producers should be strongly encouraged to do this.
Occasionally circumstances may make this impossible. If for some reason the meters are not used the following technique can be used to get the best possible results. The recommendation is to remove the milking unit from the cow approximately half-way through milking and collect an equal volume of milk from each quarter (a composite sample) in the sample vial. Samples of foremilk and strippings are not appropriate. At the beginning and the end of milking the SCCs is high. Samples collected at these times may suggest a cow is infected when in fact she is not.
What is the proper technique for collecting samples for culture at the lab to identify the bacteria causing mastitis?
Milk samples for culture are collected at milking time after teat disinfection and before the unit is applied. The steps are:
This winter OMAF vets, Raw Milk Quality staff and Livestock Advisors conducted 20 workshops about mastitis for producers. Collecting milk samples to identify mastitis-causing bacteria in cow milk samples was a topic discussed and emphasized. During these sessions many questions arose and were discussed concerning when and how to collect the necessary milk samples.
When visiting farms and collecting samples for Ontario DHI, you may be (or may already have been) asked the following questions. I'm providing some answers to help you with this and to clear up some misconceptions producers seem to have. I welcome your comments and questions.
Can DHI samples be used for bacterial culture?
No. DHI samples cannot be used for mastitis culture because they have a preservative added. This prevents bacterial growth which is needed for mastitis bacteria identification in the lab. Also, samples for culture must be kept refrigerated or frozen between collection and arrival at the lab.
Can samples for bacterial culture be collected from the meters like DHI SCC and composition samples?
No. Although the meters and milking equipment are routinely cleaned and sanitized some bacteria may be added to the milk in passage. This is not enough to cause milk quality problems such as elevated plate loop counts (PLCs). However, if these bacteria are in the samples collected from the meters and grow on the cultures at the mastitis diagnostic lab it is impossible to determine whether the bacteria came from a mastitis infection in the cow or from the milking equipment. Additionally, these equipment bacteria multiply rapidly and can "overgrow" or hide mastitis bacteria so that they cannot be identified by the lab technician.
Is the culturing done in the same lab as the SCC testing?
No. Individual cow SCC testing is done at DHI in Guelph. Individual cow cultures are done by the labs that used to be part of OMAF but, as of April 1st, 1997, are part of the University of Guelph. There are two labs doing mastitis culture, one in Kemptville and one in Guelph. Some veterinary practises also offer this service on a limited basis.
If more than 10 samples are to be submitted to the veterinary diagnostic lab for culture the producer, or the producer's veterinarian, must contact the lab in advance to book a date.
How do I collect milk samples for SCC testing when the meters are not being used? (this situation arises when producers enrol in the 4 SCC tests but are not on routine production testing).
The best way to obtain consistent and interpretable SCC results is clearly to use meters to collect the milk samples. Producers should be strongly encouraged to do this.
Occasionally circumstances may make this impossible. If for some reason the meters are not used the following technique can be used to get the best possible results. The recommendation is to remove the milking unit from the cow approximately half-way through milking and collect an equal volume of milk from each quarter (a composite sample) in the sample vial. Samples of foremilk and strippings are not appropriate. At the beginning and the end of milking the SCCs is high. Samples collected at these times may suggest a cow is infected when in fact she is not.
What is the proper technique for collecting samples for culture at the lab to identify the bacteria causing mastitis?
Milk samples for culture are collected at milking time after teat disinfection and before the unit is applied. The steps are:
1. Wash and dry the cow's teats using individual paper towels.
When doing this, do the two teats on the far side of the cow first, followed
by the two closest.
2. Remove one quick stripping of milk from each quarter. Collect this discarded milk in a strip cup or bucket.
3. Use an alcohol swab to scrub the end of each teat thoroughly. Scrub the four points of the compass to ensure all dirt is removed.
4. Remove the lid of the sample vial without touching the edges of the lid or the vial. Hold the lid in the same hand as the vial, facing downwards, while collecting the milk sample. Tilt the sampling vial while collecting the milk to reduce the chances of dust or dirt dropping from the udder into the vial. When collecting a composite sample (milk from each of the 4 teats in 1 vial) sample the teats closest to you first, followed by the two on the far side. This reduces the chance of contaminating the clean teats with your hands or arms reaching across under the cow before the samples are collected. The saying to remember the washing and sampling order is:
2. Remove one quick stripping of milk from each quarter. Collect this discarded milk in a strip cup or bucket.
3. Use an alcohol swab to scrub the end of each teat thoroughly. Scrub the four points of the compass to ensure all dirt is removed.
4. Remove the lid of the sample vial without touching the edges of the lid or the vial. Hold the lid in the same hand as the vial, facing downwards, while collecting the milk sample. Tilt the sampling vial while collecting the milk to reduce the chances of dust or dirt dropping from the udder into the vial. When collecting a composite sample (milk from each of the 4 teats in 1 vial) sample the teats closest to you first, followed by the two on the far side. This reduces the chance of contaminating the clean teats with your hands or arms reaching across under the cow before the samples are collected. The saying to remember the washing and sampling order is:
"wash towards (you), sample away".
5. After the milk sample is collected replace the lid making
sure the vial is tightly closed. Label the sample with the cow's identity.
6. Refrigerate samples immediately after collection and ship them to the lab by courier with cold packs to keep them cool. Samples should arrive at the lab within 24 hours of collection.
Author:
Ann Godkin - Veterinarian/OMAF
Creation Date:
August 1997
Last Reviewed:
August 1997
6. Refrigerate samples immediately after collection and ship them to the lab by courier with cold packs to keep them cool. Samples should arrive at the lab within 24 hours of collection.
Author:
Ann Godkin - Veterinarian/OMAF
Creation Date:
August 1997
Last Reviewed:
August 1997
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