Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Animal, Dairy, and Veterinary Sciences

Department name when degree awarded

Dairy Industry


Production records for dairy cows were first based on the yield of butter for a seven day period any time during the lactation. Later, 365- day records based on production for one day in each calendar month came into general use. The records preferred at present are 305- day records based on monthly test day production, but calculated using the centering date method. The centering date estimate is based on milk and butterfat production from two consecutive milkings per month. The sampling day is centered as nearly as possible in the test month period which need not coincide with the calendar month.

The reason for the general acceptance of the 305- day records is the desire of the dairyman to freshen the dairy cow annually, which means milking for ten months and dry for two months. Records calculated by the centering date method more nearly represent actual production than records calculated by other methods that have been used.

It is generally accepted that if the present testing program is used properly it can be of great value to the dairy farmer from the standpoint of herd improvement and for selecting animals for a breeding program. However, only a small percentage of the dairymen take advantage of a testing program. One of the limiting factors has been the cost of testing and record keeping. It has been suggested that bimonthly or trimonthly test periods might provide as much information as the monthly testing interval and at the same time reduce the cost to the individual dairymen. It is reasonable to speculate that with reduced costs there would be an increased number of herds tested. This would help compensate the testing supervisor and data processing center for lost income resulting from less frequent testing, and at the same time provide more information for national sire proving programs.

However, bimonthly or trimonthly testing have not been accepted because of the possiblilty of larger error being involved in individual records. This larger error occurs because the curvelinear shape of the lactation is not taken into account and a cow is given credit for the same production over the entire testing period, resulting in either under or over estimation of the record.

Tho objective of this study is to measure the relative accuracy of estimating 305- day production of dairy cows by using different testing intervals and different methods to estimate production. Monthly, bimonthly, and trimonthly intervals are studied. Methods include the centering date method and three methods using factors designed to extend production from each test day to a 305-day estimate with the test day estimate averaged to determine the final estimate of production for 305 days.

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