Select Sires

SELECTIONS - Summer 2003
Putting Inbreeding Into Perspective

by Charles Sattler, vice president, dairy progeny testing and genetic research

Editor's note: This is the second in a two-part series on inbreeding. The entire article is at www.selectsires.com. Click on News & Info, then Animal Health, Diseases and Genetic Recessives.

Chuck Sattler

Recently, Kent Weigel, University of Wisconsin, Madison, studied strategies for using inbreeding estimates in mating decisions. He used data from A.I. sires and cows from 25 registered-Holstein and 25 registered-Jersey herds. This research showed that the optimum strategy is to calculate a genetic value for each prospective mating and adjust for the level of expected inbreeding, then use the mating with the highest adjusted value. This strategy slightly reduced the amount of genetic progress made, but did the most effective job of controlling inbreeding. The study did not consider any potential gains from corrective matings.

While this seems like an obvious solution, it is easier to describe in research settings than to carry out in real-life situations. It takes sophisticated calculations to get a genetic value for each animal. Then that value has to be adjusted for inbreeding depression. It also requires complete pedigree information that isn’t available in most cases. However, this is the best strategy for mating registered cattle and is an excellent way for these breeders to capture the investment made in maintaining pedigree records.

The Holstein Association USA Web site provides a free inbreeding calculator that does a good job of demonstrating this procedure one cow at a time. We used this feature to find the best mate for a cow with a sire stack of DURHAM x 7HO3948 MJR Blackstar EMORY-ET*TV x 9HO1294 Lylehaven AMBITION-ET x Lutz-Brookview BELL REX-ET. The mating sires considered were 7HO5687 Sandy-Valley FORBIDDEN-ET*TV, 9HO2575 Peckenstein Form BRET-ET*TM, TV, 7HO6055 D-P-M Rudolph BRIGHT-ET*TV and 7HO5682 Silver-Shade MB SAUNDERS-ET*TV (see Table 3).

Table 3. Results from Holstein Association USA's inbreeding calculator for potential sire choices for a cow with a sire stack of DURHAM x EMORY x AMBITION x REX.

Potential Mate	Pedigree	Actual TPI™	Inbreeding Coefficient	Adjusted TPI*
9HO2575 BRET	FORMATION x ESQUIMAU	+1611	4.5%	+1611
7HO6055 BRIGHT	RUDOLPH x ROEBUCK	+1559	3.9%	+1572
7HO5682 SAUNDERS	BELLWOOD x AEROSTAR	+1562	4.7%	+1562
7HO5687 FORBIDDEN	EMORY x MASCOT	+1616	10.3%	+1497
February 2003 data *adjusted for inbreeding depression

This exercise shows that inbreeding does affect the mating result. If inbreeding were ignored, FORBIDDEN would be chosen for the highest TPI. But, he is closely related to the cow being considered. After accounting for inbreeding depression, BRET becomes the best choice. This also shows that the best choice may not have 0 percent inbreeding or even be the one with the least inbreeding. This strategy finds the balance between genetic gain and inbreeding depression.

The inbreeding values of mating this cow to BRET, BRIGHT or SAUNDERS are typical of what we see when complete pedigree information is available. The average inbreeding value for Holsteins born in 2000 and included in USDA genetic evaluations is 4.5 percent. The corresponding average for Jerseys is 6.2 percent.

In most situations, complete pedigree information is not available, so going through all these calculations is overkill. Weigel’s research studied a second strategy that used only matings that were below a fairly strict level of inbreeding. He found this approach reduces inbreeding as well as produces overall selection results close to the more sophisticated methods described above.

In most management systems, the simplified approach works well. Select Mating Service™ (SMS™) uses this threshold strategy. It uses a default inbreeding threshold of 3.125 percent when four generations of pedigree information is available. SMS does not recommend a mating where the sire and dam have grandparents in common.

Here are a few guidelines you can use to manage inbreeding in your herd:

Record pedigree information. The more pedigree information you have available, the better control you'll have of inbreeding in your herd.
Breed for cows that will please you. Don't give up striving for improved functional type and consistency. Aggressively avoiding inbreeding may produce cows that are below your standards for important functional traits.
Use a mating program. With the widespread use of artificial insemination, the pedigrees of dairy cattle have gotten complicated. Mating programs, like SMS, help organize pedigree information and avoid the mating of highly related animals.
Use a variety of pedigrees. Look for bulls that have some variety in their pedigrees, but still meet your production and type standards. Using a diverse group of bulls will provide more mating options today and in the future.

™Select Mating Service and SMS are trademarks of Select Sires Inc.
™TPI is a trademark of Holstein Association USA

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