Aseptic Technique: Procedure for Collecting Milk Samples

Milk sampling is the first step one takes when working towards identifying a problem with the milk or the animal that produced that milk. Aseptic technique will help you ensure that you do not expose the milk to contamination/cross-contamination.

The individual carrying out the sampling activity should be extra careful to adhere to all the procedures for sample collection. Certain diseases associated with milk, e.g. mastitis or tuberculosis, may result from the bacteria from the animal or the handler.

Aseptic technique will also help you correctly identify the causative organisms to facilitate proper administration of correct medication. These causative microorganisms can come from the cows’ skin, udder, and teats as well as on the hands of the sampler. Do not forget about the barn/cowshed environment.

Contamination of samples will result in misdiagnosis, which will cause increased production costs, confusion, and frustration. One can be able to avoid contamination during sampling by following the following procedures:

Aseptic technique: required sampling materials

Sterile vials or sampling tubes
70% alcohol (ethyl or isopropyl)
Cotton balls soaked in 70% alcohol (could also be commercially prepared, individually packaged alcohol swabs)
Cooler box with ice or freezer packs for storing samples
Racks for holding sample tubes/vials used to sample cows, and for sample storage in the cooler
Disinfectant for cleaning teats (effective germicidal products for pre-milking teat disinfection are recommended)
Paper towels or individual cloth towels (be careful, sharing towels could easily lead to cross contamination)
Means of identifying samples: permanent ink pen (with ink that is stable in both water and alcohol) or typed labels

Aseptic technique: sampling procedure you should follow

Label the tubes prior to sampling (capture such information as the date, farm, cow, and quarter where you get the sample from).
Brush loose dirt, bedding, and hair from the udder and teats. Thoroughly wash and dry very dirty teats and udders before you start sampling. ONLY WASH UDDERS AS A LAST OPTION.
Streak the first few streams of milk (strict fore-milk) and observe milk and mammary quarters for signs of clinical mastitis. Record all observable clinical signs.
Dip all quarters in an effective pre-milking teat disinfectant and allow at least 30 seconds contact time.
Dry the teats using an individual towel.
Beginning with teats on the far side of the udder (relative to your side), scrub teat ends vigorously for 10 to 15 seconds with cotton balls moist, but not dripping wet, with the 70% alcohol. Scrub teat ends until no more dirt appears on the swab or on the teat end. Use only one swab per teat and take care not to touch clean teat ends. Also take precaution so that the clean teats do not come into contact with dirty tail switches, feet, and legs. If you are dealing with a difficult herd, begin by scrubbing the nearest teat until clean, obtain the sample, and move to the next teat.
Begin sample collection from the closest teat. You then move to teats on the far side of the udder relative to your side.
Remove the cap from the sampling tube/vial but do not put the cap down or touch the inner surface of the cap. Ensure you keep the open end of the cap facing downward the whole time.
Maintain the tube/vial tilted at about 45-degree angle while sampling. Do not allow the lip of the sample tube to touch the teat end.
Collect one to three streams of milk and immediately securely recap the tube/vial. Do not overfill tubes, especially if you have to freeze the samples otherwise, they may spill/get exposed to contaminants.

To collect a composite sample (milk from all four quarters in the same tube). Begin sample collection with the nearest teats and progress to the teats on the far side of the udder. You should collect 1 or 2 ml of milk from each quarter of the udder. When you take samples at the end of milking or between milking sessions, you should dip the teats in an effective germicidal teat disinfectant following sample collection. Store samples immediately in the cooler box containing ice or in a refrigerator. Immediately freeze samples that you will culture at a later date or more than 48 hours after collecting the samples.