To Buy or Not To Buy a Digital Refractometer
Digital refractometers are now available in the price range of $350 to $450 that can be used to assess the quality of colostrum, estimate dry matter content of milk and evaluate blood serum total protein.
A question that came up today is whether or not these digital units are more accurate than the hand-held style analog refractometers. Part of the answer is found in the specifications of the unit that is purchased. The digital units will specify resolution and precision (+/-).
Another part of the answer when you compare the two styles is whether or not the units are automatically temperature compensated. And, how recently have the the units been calibrated?
Another part of the answer is user-related. All of us that have used the hand-held analog units know the challenge of interpreting where the boundary line crosses the scale divisions. My experience is that blood serum total protein samples have fairly sharp boundary lines, milk samples for dry matter are more fuzzy and colostrum quality sample boundary lines are very fuzzy.
The values assigned for a sample get more and more subjective as the level of fuzziness goes up. Thus, if more than one person at the dairy is taking readings the potential for variation among persons is much higher with analog units than with digital ones. That is, with a digital unit the readings are more consistent and less dependent on who takes the reading.
Maybe the more important question is how accurate do we need to be when using the information to make on-farm decisions? Is a difference of 0.1 in a blood serum total protein reading going to change the decisions we make in colostrum management? When we assess dry matter content of milk how large a difference from our target value do we need to have in order to add milk powder? If our Brix target for colostrum is 22 are we willing to live with values that are accurate plus/minus 1.0?
My opinion is that whether or not to purchase the multi-scale digital unit is mostly a matter of convenience rather than either accuracy or consistency. One unit is used regardless of the medium to be evaluated. Plus, as a guy I enjoy having high tech stuff around.