Looking for the right way to convert to U.S. PTA?

Dr. Rex Powell,* Dr. Martin Sieber, and Ms. Suzanne Hubbard*
*Animal Improvement Programs Laboratory, Agricultural Research Service, United States Department of Agriculture, Beltsville, Maryland 20705-2350, USA
National Association of Animal Breeders, P.O. Box 1033, Columbia, Missouri 65205, USA

The preferred way to compare the genetic merit of bulls from different countries is to have the evaluations all expressed on the same scale. Fortunately, most bulls of interest have International Bull Evaluation Service (Interbull) evaluations for milk, fat, and protein yields. The file of official evaluations on the U.S. scale is available from the Animal Improvement Programs Laboratory's (AIPL's) internet web site www.aipl.arsusda.gov. Searches also can be made for individual bulls by registration number, name, or partial name.

Evaluations on the desired scale may not always be conveniently available. Dairy farmers may see an advertisement for a bull on another country's scale and wonder what the bull's evaluation would be on a U.S. scale. Or they may see (or be told) what a bull's evaluation would be on the U.S. scale. The main purpose of conversion equations is to convert from one scale to another for bulls without Interbull evaluations for milk, fat, and protein yields. They also can be used to get an approximate idea of what a bull's evaluation might be on a U.S. scale as a check on marketing practices. The conversion equations developed by Interbull to convert evaluations from other countries' scales to a U.S. basis are available at the AIPL web site.

The following tables are a convenient reference for estimating the genetic merit for milk, fat, and protein yields of Holstein bulls from other countries that would be equivalent to certain U.S. predicted transmitting abilities (PTA's) in pounds. For example, a bull that has a Netherlands estimated breeding value (EBV) of 1700 kg for milk yield would be expected to be similar to a U.S. PTA of about 2000 pounds. A word of caution: This conversion is only approximate ... the actual PTA milk from Interbull would be different. Typically, however, the difference is less than 100 pounds.

Remember that the tables are directional. You can approximate a U.S. PTA from an EBV from one of the listed countries, but the tables are not valid for estimating EBV's of other countries from a U.S. PTA or from EBV from other countries. Be sure that you have a current evaluation on one of the other scales and that the evaluation is in the correct units (PTA versus EBV, pounds versus kilograms) for the other country.

Interbull and most national evaluations now are calculated four times each year, which makes it difficult to keep promotional material up to date. At the least, customers need to know the evaluation date for any information that they view. The reference tables that follow are based on equations that were developed from November 1998 Interbull evaluations. Although the equations will change with each subsequent evaluation, the changes usually are expected to be small. However, when a country changes the definition of its genetic base population as occurs with the first evaluation of each year in Canada and with the mid-year evaluation in France, knowing the evaluation date becomes even more important because changes in conversion equations can be quite dramatic when bases change.

Buyers need to be wary of semen sellers that present evaluations in units other than those that are official for a country's scale. For example, advertising that a bull with an EBV for milk of 1000 kg has an EBV of 2200 pounds would be improper and unethical, just as it would be for a seller of U.S. semen to represent a 1000-pound PTA as a 2000-pound EBV. Although, EBV is twice PTA and a kilogram is about 2.2 pounds, no country has a scale expressed as pounds of EBV. Legitimate units are pounds of PTA for the United States; kilograms of PTA for the United Kingdom, Ireland, and Israel; relative breeding values for Scandinavian countries; and kilograms of EBV for all other countries that participate in Interbull evaluations. The best option always is to use the national or Interbull evaluations on a single scale.

Approximate* U.S. predicted transmitting abilities (PTA's) in pounds for Holstein milk yield that correspond to estimated breeding values (EBV's) in kilograms (November 1998):

United States Canada France Germany Italy Netherlands Spain
PTA milk
(pounds)
EBV milk
(kilograms)
EBV milk
(kilograms)
EBV milk
(kilograms)
EBV milk
(kilograms)
EBV milk
(kilograms)
EBV milk
(kilograms)
0 20 -449 711 524 225 402
250 308 -203 931 706 409 542
500 597 44 1152 889 594 682
750 886 290 1372 1071 778 822
1000 1174 537 1592 1253 963 962
1250 1463 783 1813 1436 1147 1102
1500 1752 1030 2033 1618 1332 1241
1750 2040 1276 2253 1800 1516 1381
2000 2329 1523 2473 1983 1701 1521
2250 2618 1770 2694 2165 1885 1661
2500 2906 2016 2914 2348 2070 1801
2750 3195 2263 3134 2530 2254 1941
3000 3484 2509 3354 2712 2439 2081

*Valid only for approximate conversion from EBV in kilograms to U.S. PTA in pounds from November 1998 through January 1999.
Source: Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, Maryland, USA.

Approximate* U.S. predicted transmitting abilities (PTA's) in pounds for Holstein fat yield that correspond to estimated breeding values (EBV's) in kilograms (November 1998):

United States Canada France Germany Italy Netherlands Spain
PTA fat
(pounds)
EBV fat
(kilograms)
EBV fat
(kilograms)
EBV fat
(kilograms)
EBV fat
(kilograms)
EBV fat
(kilograms)
EBV fat
(kilograms)
0 -6 -25 4 16 -13 12
10 6 -14 13 24 -5 18
20 17 -4 22 31 4 24
30 29 7 31 39 12 30
40 40 17 40 46 20 36
50 52 28 49 54 28 42
60 63 39 58 61 36 48
70 75 49 68 68 44 54
80 86 60 77 76 53 60
90 98 71 86 83 61 66
100 109 81 95 91 69 72
110 121 92 104 98 77 78
120 132 103 113 106 85 84
130 144 113 122 113 93 90

*Valid only for approximate conversion from EBV in kilograms to U.S. PTA in pounds from November 1998 through January 1999.
Source: Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, Maryland, USA.

Approximate* U.S. predicted transmitting abilities (PTA's) in pounds for Holstein protein yield that correspond to estimated breeding values (EBV's) in kilograms (November 1998):

United States Canada France Germany Italy Netherlands Spain
PTA protein
(pounds)
EBV protein
(kilograms)
EBV protein
(kilograms)
EBV protein
(kilograms)
EBV protein
(kilograms)
EBV protein
(kilograms)
EBV protein
(kilograms)
0 -2 -20 11 16 -2 9
10 9 -11 19 24 5 14
20 20 -1 27 32 12 20
30 31 8 36 40 19 25
40 42 18 44 48 26 31
50 53 27 52 56 33 36
60 64 37 60 64 41 42
70 75 46 69 72 48 48
80 86 56 77 80 55 53
90 97 65 85 88 62 59
100 108 75 93 96 69 64
110 119 84 101 104 76 70

*Valid only for approximate conversion from EBV in kilograms to U.S. PTA in pounds from November 1998 through January 1999.
Source: Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, Maryland, USA.