By George
Wiggans
USDAARSAIPL
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 testday estimates. Protein yield is calculated from the measured percentage and the adjusted milk yield.
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:
Estimated Testday milk yield  =  Measured milking yield × Milkinginterval factor^{1} + 
(DIM158) × Milkingintervallactationstage cofactor  
^{1}For a.m. or p.m. milking time. 
Table 1. Factors for estimating daily milk yield for 2X milking with one weighed/sampled milking.  
Milking
Interval (hrs) 
Milk adjustment factors  Percent fat adjustment factors  
For measured milking started in a.m.  For measured milking started in p.m.  
Milkinginterval factor  Milkingintervallactationstage cofactor  Milkinginterval factor  Milkingintervallactationstage cofactor  Milkinginterval factor  
<9.00  2.465  0.01566  2.594  0.00834  0.919 
9.00 9.24  2.465  0.01566  2.534  0.01069  0.927 
9.25 9.49  2.465  0.01566  2.477  0.01071  0.934 
9.50 9.74  2.411  0.01578  2.423  0.01126  0.941 
9.75 9.99  2.359  0.01600  2.370  0.01043  0.948 
10.0010.24  2.310  0.01010  2.321  0.00742  0.955 
10.2510.49  2.262  0.00879  2.273  0.00471  0.961 
10.5010.74  2.217  0.00649  2.227  0.00000  0.968 
10.7510.79  2.173  0.00492  2.183  0.00000  0.974 
11.0011.24  2.131  0.00000  2.140  0.00000  0.980 
11.2511.49  2.091  0.00000  2.099  0.00000  0.986 
11.5011.74  2.052  0.00000  2.060  0.00000  0.992 
11.7511.99  2.014  0.00000  2.022  0.00000  0.997 
12.0012.24  1.978  0.00000  1.986  0.00000  1.003 
12.2512.49  1.943  0.00000  1.951  0.00000  1.008 
12.5012.74  1.910  0.00000  1.917  0.00000  1.013 
12.7512.99  1.877  0.00000  1.884  0.00000  1.018 
13.0013.24  1.846  0.00000  1.852  0.00418  1.023 
13.2513.49  1.815  0.00000  1.822  0.00510  1.028 
13.5013.74  1.786  0.00369  1.792  0.00678  1.033 
13.7513.99  1.757  0.00569  1.763  0.00747  1.037 
14.0014.24  1.730  0.00766  1.736  0.01123  1.042 
14.2514.49  1.703  0.00801  1.709  0.01039  1.046 
14.5014.74  1.677  0.00733  1.683  0.01000  1.050 
14.7514.99  1.652  0.00696  1.683  0.01000  1.054 
>=15.00  1.628  0.00518  1.683  0.01000  1.058 
Milkinginterval factors are calculated with the formula:  
Milkinginterval factor  =  1 / Intercept + (Slope × Milking interval)  
where the intercept and slope are as follows:  


The fat percent milkinginterval adjustment factor is the ratio of the fat yield adjustment factor to the milk yield adjustment factor. The values for percent fat adjustment given in Table 1 are appropriate for both a.m. and p.m. milkings. 
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.
Testday milk yield  =  (1.703 × 23.0#) + (0.00801) × (250d  158) 
=  38.4 pounds of milk  
Testday fat percentage  =  1.046 × 4.0 
=  4.2% fat  
Testday fat yield  =  0.042 × 38.4# 
=  1.61 pounds of fat  
Testday protein percentage  =  3.5% protein 
Testday protein yield  =  0.035 × 38.4# 
1.34 pounds of 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 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 G2.)
Milkinginterval factors are calculated using the same formula with the intercept and slope as follows:  


When 2 milkings are included for sampling, the intercepts and intervals for both milkings are included in determining a factor for calculated estimated milk yield that is applied to the total yield from both milkings.  
Milkinginterval factor  =  1 / (Intercept 1 + Intercept 2)+ (Slope × (Milking interval 1 + Milking interval 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.
Milkyield factor  =  1 / {0.077 + 0.068 + [0.0329 × (10h + 7h)]} 
=  1 / 0.704  
=  1.42  
Testday milk yield  =  1.42 × (16.0# + 12.0#) 
=  39.8 pounds of milk  
Percentfat factor  =  [0.077 + (0.0329 × 10h)] / [0.186 + (0.0186 × 10h)] 
=  0.406 / 0.372  
=  1.09  
Testday fat percentage  =  1.09 × 4.0 
=  4.4 % fat  
Testday fat yield  =  0.044 × 39.8 
=  1.75 pounds of fat  
Testday protein percentage  =  3.5% protein 
Testday protein yield  =  0.035 × 39.8 
1.39 pounds of protein 
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.