DHI Notes...
Mar 08 | Keep time in mind when interpreting DHI numbers | Bennet Cassell
The numbers in the table above are not all based on the same period of time. Yes, they were all part of the state average for the same month – February 2008 in this case. But they contain different kinds of information. Rolling herd average milk is an example of a number that is influenced as much by what happened a year ago as it is by what happened in the days before the February 2008 test. Rolling herd average reflects the annual (365 d) milk production of an “average” cow in a herd over the past 12 months. As a new month of average daily yield is added, the oldest month in the previous average is dropped. The data on which rolling herd averages are based were collected over the past year. Days open is also a dated number because it is affected by reproductive decisions and practices that go back as far as the previous calving date on any cow still in the breeding herd. Cows more recently fresh add more recent information than cows in the dry pen or with long days in milk. Peak yields, interval to first breeding and NM$ of service sires also are based on events from the recent past. A major change in management from a couple of weeks ago won’t affect these figures very much for some time to come. Last month’s average SCS from the table above would be an example of information based on recent events. Only SCS from the last test day affects this number. Of course, with SCS, the conditions that lead to chronic high cell counts in some cows affect herd average SCS as long as the cows are in the herd. Back before the introduction of on farm computers, all DHI data were dated, as the most recent information came from last month’s test. Today, PCDART allows herds to change important management information such as results of reproductive exams as soon as the dairy producer can enter the data into a computer. Both very recent and more historic information are useful in herd management decisions as long as managers understand how the numbers are calculated and how they might best be used. If you aren’t sure what a number means, or want to know more about any of your DHI records, do feel free to call on me or other Virginia Extension personnel.
State DHI averages for important management areas in February 2008:
Management area
February 2008
Change from last year
Rolling herd average milk Peak yield in heifers Days to first breeding Days open Net Merit of proven service sires Herd turnover less dairy sales (%) Monthly average SCS Feed cost per cwt. (milking cows) Milk blend price Bennet Cassell
Genetics and Management
