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; current address: AgDevelop, 2012 Cherry Hill
Drive, Suite 202-F, Columbia, Missouri 65203, 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 (http://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 most recent conversion equations developed by Interbull to convert evaluations from other countries' scales to a U.S. basis are available at the AIPL web site (http://aipl.arsusda.gov/reference/ib/convert.shtml).
The tables linked below are a convenient reference for estimating the genetic merit for milk, fat, and protein yields of bulls from other countries that would be equivalent to certain U.S. predicted transmitting abilities (PTA's) in pounds. For example, a Holstein bull that had a Netherlands estimated breeding value (EBV) of 1600 kg for milk yield in May 2005 would be expected to be similar to a May 2005 U.S. PTA of about 1700 pounds. A word of caution: This conversion is only approximate ... the actual PTA milk from Interbull could 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's 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 4 times each year, which makes keeping promotional material up to date difficult. 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 the most recent Interbull evaluations. Although the equations change with each subsequent evaluation, the change between subsequent converted evaluations usually is expected to be small. However, when a country changes the definition of its genetic base population, 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.
Tables with approximate U.S. PTA's in pounds that correspond to EBV's in kilograms: