Consideration of Percentage of Milk Shipped for Calculation of Total Lactation Yields from Various Morning and Evening Plans of Milk Sampling

¹ Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350
² National DHIA, Columbus, OH 43231-4078

Milk yield recorded on DHI test day was compared with data on milk shipped from Texas and Minnesota herds for an innovative DHI test plan referred to as alternate a.m.-p.m. without a timer. Controls were yields for test day and for milk shipped from official DHI herds in Texas, Illinois, Minnesota, and several northeastern US states. Herd milk yield for a test day as a percentage of milk shipped was considered to be an indicator of the accuracy of the DHI recording plans. Mean percentage of milk shipped was 103 for all plans and regions. When herd test days with missing values were excluded, the percentages of herd test days within 96 to 110% of milk shipped were 77 for Texas and 82 for Minnesota, 79 for Illinois, and 81 for northeastern official plans. Analysis indicated that the percentage of milk shipped was consistent across herd sizes, data source, and milk yield.

Eight hypothetical testing plans were examined with or without adjustment of lactation yields for percentage of milk shipped. Estimates of variance components of lactation milk yields were computed and compared using a multitrait animal model. Adjustment of records for percentage of milk shipped would decrease mean milk yields by 3%, could result in better estimates of actual milk produced, but would have little effect on accuracy of genetic evaluations.

Key Words: genetic evaluations • innovative testing plans • accuracy • test day

Submitted on May 25, 1995
Accepted on October 10, 1995