Estimating daily yields when not all milkings are weighed and sampled (AP Plans)

By George Wiggans
USDA-ARS-AIPL

Over the past several years, official milk testing plans have become more flexible. Most tested cows are on AM/PM programs for which data are provided from only one milking (alternately a.m. and p.m) per month. In 2003, all milkings were weighed for only 36% of cows and only 23% had component samples taken for all milkings on test day. Total daily yield must therefore be estimated for nearly two thirds of all test day records.

Milk and fat yield estimates are based on measured yield and milking frequency. An adjustment factor accounts for differences in the average milking interval (expressed in decimal hours) between the preceding milking and the measured milking, and the time of day of the measured milking (started in a.m. or p.m.). For 2X milking, an additional adjustment is applied to milk yield for the interaction between milking interval and stage of lactation, with mid lactation (158 DIM) set to zero. Milking interval does not affect protein and SNF percentages and so the percentages for the sampled milking are used for test-day estimates. Protein yield is calculated from the measured percentage and the adjusted milk yield.

For 2X Milking:

For 2X milking herds, a single milking or both milkings may be weighed. The sample may be collected at one or both of these milkings. When one milking is weighed and sampled, yield is estimated as follows:

For example: Cow A is in the herd with a measured milking started at 6:30 a.m. and a milking interval of 14.25 hours. She has been in milk for 250 days. She produced 23.0 pounds of milk at the measured milking, and her sample was 4.0 % fat and 3.5 % protein.

If both milkings are weighed, but only one is sampled, daily milk weight is the sum of weighed milkings, and fat percent is calculated as above. Fat and protein yield are calculated using the total daily milk weight.

For 3X Milking:

For 3X herds, a single milking or two consecutive milkings may be weighed. The sample may be collected at one or both of these milkings. Stage of lactation × milking interval adjustments are not used for greater than 2× milking.

These AP factors for estimating daily yields in 3X herds should not be confused with factors that adjust 3X records to a 2X basis. (See DHIA Fact Sheet G-2.)

Milk and fat percent factors are calculated separately based on the number of milkings weighed or sampled.

For Example: Cow B is in a herd that had 2 of 3 milkings weighed of which 1 was sampled. She produced 16.0 pounds of milk at a 5 a.m. milking and 12.0 pounds of milk at a noon milking. Her sample at the 5 a.m. milking was 4.0 % fat and 3.5 % protein. The milking preceding the 5 a.m. milking started at 7 p.m. the evening before.

For 4X - 6X Milking:

The intercept terms for calculating 3X factors (0.077, 0.068, and 0.066) are multiplied by the factor [3 / (milkings per day)] for use in calculating factors for milking frequencies greater than 3X. See http://aipl.arsusda.gov/reference/freqadj.pdf for further explanation of the 3X AP factors.