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United States Department of Agriculture

Agricultural Research Service

Title: Genetic Evaluations for True Protein

Authors
item Vanraden, Paul
item Powell, Rex

Submitted to: AIPL Research Reports
Publication Type: Government Publication
Publication Acceptance Date: July 1, 2000
Publication Date: N/A

Interpretive Summary: True protein measures only the proteins in milk, whereas crude protein measures all sources of nitrogen and includes nonprotein nitrogen, which has no food value to humans and is a waste product when making cheese and other manufactured products. Most U.S. farmers are now paid for true rather than crude protein. To be consistent with milk purchasers, the U.S. milk-recording system switched from measuring crude to true protein in milk on May 1, 2000. Beginning in August 2000, U.S. genetic evaluations for protein will estimate genetic merit for true instead of crude protein. The percentage of milk that is true protein is lower than the percentage that is crude protein by an approximate difference of .19%. Estimated genetic merit for true and crude protein percentages are the same. However, a genetic evaluation for true protein yield (lb) generally is smaller (closer to 0) than for crude protein because a smaller fraction of the milk is considered to be protein. For those few bulls with a positive evaluation for milk but a negative evaluation for crude protein yield (or vice versa), the evaluation for true protein yield is slightly greater (farther from 0) than for crude protein. For Holstein bulls that were designated as being in active artificial-insemination service in February 2000, the average protein evaluation changed from 54 lb for crude protein to 51 lb for true protein, but little reranking of the bulls occurred. Although the U.S. dairy industry had expressed a concern about whether other countries report and pay for true or crude protein, international genetic rankings are not affected by a nation's choice of protein measure because changes related to use of crude or true protein are accounted for by equations that are used to combine national data.

Technical Abstract: True protein measures only the proteins in milk, whereas crude protein measures all source of nitrogen and includes nonprotein nitrogen, which has no food value to humans and is a waste product when making cheese and other manufactured products. Most U.S. farmers are now paid for true rather than crude protein. To be consistent with milk purchasers, the U.S. milk-recording system switched from measuring crude to true protein in milk on May 1, 2000. Beginning in August 2000, U.S. genetic evaluations for protein will estimate genetic merit for true instead of crude protein. The percentage of milk that is true protein is lower than the crude protein percentage by a difference of .19%. Predicted transmitting abilities (PTA's) for true and crude protein percentages are the same. However, PTA for true protein yield generally is closer to 0 than PTA for crude protein yield. For those few bulls with positive PTA milk but negative PTA for crude protein yield (or vice versa), PTA for true protein yield is slightly farther from 0 than PTA for crude protein. Standard deviation of PTA for true protein yield for Holsteins is .940 times standard deviation of PTA for crude protein. Correlation between PTA's for true and crude protein yields was .9993 for Holstein bulls in active artificial-insemination service in February 2000. Mean PTA for those bulls changed from 54 lb for crude protein to 51 lb for true protein, but little reranking occurred. The main result of changing from crude to true protein is to reduce standard deviation of protein yield by 5 to 6%. International genetic rankings are not affected by a nation's choice of protein measure; changes in means and variation related to use of crude or true protein are accounted for by equations used to combine national data.

Last Modified: 4/16/2014
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