Dr. Luciana da Costa, Department of Veterinary Preventive Medicine, The Ohio State University.
As basic as it looks, some producers are still not fully aware and familiarized with the importance of or how to collect a milk sample. Part of mastitis control programs consist on culturing and on the microbiological analysis of milk samples. However, to be able to identify the bacteria, strict aseptic procedures must be used when collecting the samples. Aseptic collection is extremely important to avoid contamination with bacteria present on the skin of the cow, hands of the sampler, and environment. And yet, the importance of collecting a good sample goes beyond udder health. Improper milk samples can interfere with how much producers are paid (improper samples can lead to violations for high SCC or high bacterial count). It is also detrimental for processors when evaluating milk quality (results based on an inaccurate sample can put at risk the whole tanker load of milk).
For purposes of a mastitis control program, either bulk tank or individual milk samples can be used.
- Bulk tank cultures are cheap and useful for herd screening and identification of the most common bacteria present in bulk tank, but they ARE NOT an accurate way of estimating the number or identify the infected cows in a herd.
- Individual cow milk samples are more appropriate to increase the chance of finding which organism is causing the problem.
- Composite sample (collection of milk samples from all 4 quarters into a single tube) is often used in herd screening programs. It has the benefit of reducing cost but usually provides some level of false negative results when compared to individual quarter milk samples.
Collecting Bulk Tank Milk - Most milk haulers know the importance of obtaining an accurate sample, but it also essential that producers have the knowledge as well. Some important aspects to consider are:
- Turn on the agitator for at least 10 minutes to ensure a representative milk sample is taken.
- Collect samples from the top of the bulk tank, NEVER from the tank outlet (area difficult to clean and can provide an inaccurate result). Use a clean and sanitized dipper.
- Bulk tank milk samples should be immediately refrigerated or frozen if more than 24 hours will pass until they are submitted to the laboratory for mastitis-pathogen identification. Interpretation from a SINGLE bulk tank sample results can frequently lead to inconclusive results. It should be combined with somatic cell counts, individual cow culture results, and clinical mastitis records.
Procedure to collect Aseptic Cow Milk Samples - The correct steps for taking composite sterile milk samples are:
- Use proper equipment (sterile plastic tubes/vials, label with permanent markers to identify the farm, cow, and quarter being sampled; use gloves to avoid contamination)
- Clean and dry teats and udders
- Fore-strip teats (3 to 4 streams of milk from each teat to be sampled to remove contaminated milk from the teat canal)
- Pre-dip teats with 0.5% iodine. Keep it on for 30 to 40 seconds.
- Dry teats with a single use cloth or paper towel.
- Sanitize teat ends with 70% alcohol, using special attention to sanitize the teat end.
- Take the sample – tube should be held at an angle to avoid debris and care should be exercised to not touch the inside of the cap to avoid contamination.
- Post-dip teats.
- Refrigerate or freeze samples if more than 24 hours will pass until it can be submitted to the laboratory.