Journal of Dairy Science, Vol 79, Issue 2 291-300, Copyright ©
1996 by American Dairy Science Association
Consideration of percentage of milk shipped for calculation of total
lactation yields from various morning and evening plans of milk sampling
T. R. Meinert, H. D. Norman and F. N. Dickinson
Animal Improvement Programs Laboratory, Agricultural Research Service,
USDA, Beltsville, MD 20705-2350, USA.
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
percentage of herd test days within 96 to 110% of milk shipped were
77 for Texas and 82 for Minnesota innovative plans and 82 for Texas,
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.
