QUESTION; What does per cent cow days mean? Can we use this number to manage our herd? ANSWER: Percent cow days can be found several places in reports from PA DHIA. The first place we see this number is on Herd Sum mary I, which is blue in color. 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PA DOTTERER EQUIPMENT Route 64 1-800-356-3397 It is described as “Test Period Daily Average," and the fourth column is “% Days In Milk.” We also find the same number on the backside of Herd Summary n, where it is also labeled as “Test Period Daily Averages.” The fourth column is “% Days In Milk.” Now, let us look at what this number means. At any given time, your herd has cows that are milking and some that are resting and dry. Total cows in milking herd, times (multiplied by) the days in the test period, equals the “total cows days” in the test period. The actual total days that cows were milking is the “milking days” Commander Series Trailer Sprayer GEO. V. SEIPLE & SON, INC. 1521 Van Buren Rd. 610-258-7146 MORRIS INTERNATIONAL, INC. Rt. 26 North 814-652-6101 GLEN ROCK. PA WERTZ FARM EQUIPMENT PA Route 516, RD 3 1-800-839-1992 STANLEY’S FARM SERVICE RD #1 Box 46, Off Rt. 125 717-648-2088 r prec TON. P, EROLEY FARM EQUIPMENT Salem Church Road Off Rt. 45 717-524-2408 IWN. P, SMITH FARM EQUIPMENT 30 Aucker Rd. 717-567-3562 in the test period. Milking days, divided by total days, times (multiplied by) 100, gives the “percent cow days in milk.” (Editor’s Note: Days In Milk is frequently abbreviated in dairy industry text as DIM.) Let’s look at an example: GIVEN: 1. 100 cows in a herd. 2. Days from test day to test day is 30. 3. There are 2,562 total Milk Days TOTAL DAYS - # COWS IN HERD X TEST DAY INTERVAL % COW DAYS IN MILK - MILK DAYS + TOTAL DAYS X 100. . . THEREFORE: 1. 100 X 30 - 3,000; 2. (2,562 - 3,000) = .854 .854 X 100 ° 85.4 % COW DAYS IN MILK If this same herd is reported to be at “91 % Days In Milk," then: 3,000 X 91 % - 2,730 days milked. ency a ion, LEWISBURG. P EW ALEXANDRIA. P LONE MAPLE SALES Route 119 724-668-7172 LLAND ■W H ABC GROFF, INC. 110 S. Railroad Ave, 717-354-4191 IT. PA To know if this can be a man agement tool, we must look at some factors that contribute to this number. Freshening a large num ber of cows in the period will cause an increase in percent cows days in milk. Brining new heifers into the herd at freshening will also show an increase. Drying cows off early or cows with extended dry periods will cause a decrease in percent cow days in milk. In theory, a herd that milks all cows for 305 days and then allows them to dry for 60 days would attain a percent cow days in milk o f 83.56 % ((305/365) X 100 = 83.56). This would be a goal for herds if we lived in a perfect world, but we do not. Currently the state average is 87 percent Days In Milk. This means that the average PA DHIA cows milks for 317 days and then is put dry. That is okay if we have the cow bred on time and she stands dry for 60 days. What happens when she is dry longer? Now we see that the percentage Days in Milk goes down and pro fits along with it. How do we use information like % DIM? <HARPI> ty \| wiaii I** a* Available with HARDI Pilot electronic application controller NEW RINGGOLD. PA ECKROTH BROS. FARM EQUIPMENT Rt. 443 & 895 717-943-2131 OREFIELD. PA ECKROTH EQUIPMENT 4910 Kernsville Road 610-366-2095 ID. P. LEBANON VALLEY IMPLEMENT 700 East Linden St. 717-866-7518 >H. NJ FARM RITE, INC. 122 Old Cohansey Rd 609-451-1368 Lancaster Farming, Saturday, January 2, 1999-Al7 I wish I could say that there is a number everyone should work towards, but there is not We can use this number to help analyze our herd’s milking performance. When we evaluate management changes that cause production increases for milking cows, we need to keep in mind that the parti cular change is affected by the makeup of the herd. This is how I use percentage days in milk. For instance, if a herd has pro duction increase from 67 to 71 pounds and percentage days in milk stays the same then we have a true increase. On the other hand, if % DIM increases from 78 percent to 84 percent during this same increase, then the real response to our efforts is less than the 4-pound increase that we had. In this case, a 4-pound increase is 6 percent, and coincides with a 6-percent increase in days in milk, or freshness of the herd. This is a truer evaluation of management changes, than just looking at milk response. Another example has a herd pro ducing 80 pounds per cow for three straight months. On the fourth month, the aver age drops to 73 pounds. What happened? By looking at %DIM, we see no change during the first three months. On the fourth month, this drops from 86 percent to 83 percent My read here would be that, even though we could predict that production would drop due to changes in freshness of the herd, it is too severe a drop, and something negative has occurred in our man agement scheme. The near 9-percent drop in pro duction was partly due to our herd makeup, but probably only a 2- to 3-pound loss should have been expected. We need to look at the 4- to 5-pound loss not due to herd makeup. This is my explanation of per cent Days In Milk, and how to use it to evaluate true herd performance. I am sure some of you feed peo ple out there have had the misfor tune of trying new products on farms only to fall completely flat. Use this %DIM information to realistically predict herd produc tion potential before you make unattainable promises. Again, the value of PA DHIA records shines through. ATTENTION TOBACCO FARMERS I want to thank you farmers and friends for your support and friendship for the past 2 years. I want to let you know I will not be working with or for Penn Leaf Tobacco Co. or B.S. Beiler anymore. Watch for my future ad. I want you to know I will continue to support you. Thank You Jerry Winstead
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