SHOULD A PRODUCER SLECET THEIR TESTING DATES?

Jeffrey Keown, Ph. D.

University of Nebraska-Lincoln Animal Science Department

            Quite a few DHI producers have decided to pick the dates they would like to have their herd tested.  Some producers refuse to test during the hot summer months while others like to have more tests during the milder spring and fall months.  Is this a wise management decision or are you shortchanging your herd management program and, athe the same time, wasting money on your testing?  

            Let’s look at the figure directly below.  This figure shows “Composit Lacation Curves for Thousands of Cows.”  Look at how smooth these curves look for three different situations.  One curve is for later lactation cows that are treated normally; the other three curves are for cows that have been given a long daily light period (photoperiod) BST or have been milked 3 times per day.  In all cases, the cureves are very smooth and represent exactly what every producer expects cows’ lacation curves to resemble.  Remember, these curves are generated from thousands of records so that the normal variation associated with a cow’s lactation are masked by other cows in the calculation.  In this case, if your cows all had perfect lactation curves, it would make little if any difference in the test days chosen to test your cow. 

             Composite Lactation curve for thousand of cows.

·          The Impact of Somatotropin, Milking Frequency, and Photoperiod on

Dairy Farm Nutrient Flows.

T.F.Dunlap, R.A. Kohn,G.E.Dahi, M.Varner, and R.A.Erdman.

2000 J Dairy Sci 83:968-976

            But is this beautiful shape the same for all cows?

            The answer is no – the shape of each dairy cow’s lactation curve is not perfect.  Let’s look at a more normal lactation curve for an individual cow.  Looking at this curve, you can see the variation or fluctuation in the daily milk weights due to length of day, weather conditions, fee quality, BST usage, equipment failure, etc.  You can think of many other reasons why a cow’s lactation curve might vary as shown in this graph. 

Let’s see what happens if you arbitrarily select to test on days 50, 150 and 275 during the lactation.  Are you getting a good picture of that cow’s actual production?  Absolutely not!  You are getting a grossly exaggerated idea of her production.  How can this hurt your bottom line?  First of all, you are feeding your cow based on a higher production than they are actually producing.  This can lead to excessive weight gain and other metabolic problems.  Just think how much feed you would waste if you were feeding an entire string or group based on these readings.

            Let’s look at the opposite extreme.  Let’s suppose you test on days 100, 200 and 250.  You would have the opposite problem.  You would be underestimating the actual lactation production.  This would lead to under feeding, weight loss and a continued decrease in production, since you would not be feeding your cattle so that they could never reach the higher production as shown on days 50, 150, and 275.

            What is the best way to test?  The best way to test is to test every 30-40 days.  You will get a few of the low days, but you will also get a few of the high days.  Your complete lactation production will be a much better indicator of your herd’s production than either of the two extremes. 

            There is a rationale behind the DHI testing system – the system is attempting to give you an accurate value of your herd feeding system for maximum production.  If you test at regular intervals, you can pinpoint potential management problems that need to be addressed. 

            Remember – don’t waste you money on testing by pre-selecting dates – just go, as they say, with the flow and test every 30-40 days.  Your cattle and you will be glad you did.