Much responsibly needs to be taken when testing for butterfat content.  When I am asked why the results vary so much, I feel that we owe producers a reason.  Arizona DHIA has its “butterfat machines” audited every year in November.  Not only are the machines gone through thoroughly, but standard operating procedures are also highly scrutinized.  Paul Sauvé is the national QCS Contract Auditer.  When I asked Paul this same question, he responded with the following:

When producers experience a wide variation on butterfat, their immediate response is to question the lab test.  In the vast majority of cases, the wide variation is, in fact, due to sampling variances.  All DHI and commercial testing labs across North America are controlled very carefully, and when all is working as it should be, measurement uncertainty is less than 0.03%.  Sampling uncertainty generally runs more than ten times higher than this.

What is important to understand is that the test result only quantifies what is in that two ounce vial.  It is up to the sampler to ensure that, what is in the vial, is representative of the truck, bulk tank, or silo being assessed.  We often see variation on samples greater than 0.4% butterfat.  In other words, 20 samples taken from exactly the same load will often range from 3.6 to 4.00 percent butterfat.  Factor in the lab variation of +/-0.03, and you see that the variance from the lab is of much less significant.

If producers are telling you that their fat results are varying widely, and at the same time lab QC records show testing is within standards, you can be almost 100% certain that the problem lies with the sampling process.  The first task in getting good results is to ensure that the sample in the vial is representative of the load of milk.

– Paul Sauvé, National QCS Contract Auditor

Here at Arizona DHIA, we strive to set a standard of integrity and accuracy in all of our tests that come through our labs:  Components, Microbiology, and in our field testing!