Select Sires

SELECTIONS - Fall 2002
Calving-Ease Evaluations Improved

By Chuck Sattler, vice president, dairy progeny testing and genetic research

Researchers have documented what many producers have long realized: strict selection for low calving-ease sires can lead to cows that have problems calving. With the release of the August 2002 evaluations, Holstein producers finally have the tools to select for bulls that sire easily born calves that develop into cows that deliver calves easily.

Two calving-ease values now are published for Holstein sires. One is service-sire calving ease, which indicates the expected percent of difficult births in calves of this sire when he is mated to virgin heifers (%DBH). This is the same as the traditional calving-ease value that has been available to producers for the last 20 years. Values range from 3%DBH to 20%DBH, and should be used for choosing bulls to use when breeding heifers. Sires with service-sire calving-ease values of 10%DBH or more should be used sparingly when breeding heifers.

The new value is daughter calving ease. This summarizes a combination of two factors: the ability of a bull's daughters to deliver a calf easily and the propensity for these daughters to produce calves that are born easily. The evaluations are expressed on the same scale as service-sire calving ease and indicate the expected percent of difficult births when daughters of this bull have their first calf (%DBH). Daughter calving-ease values will range from 4%DBH to 15%DBH.

Reliability of daughter calving ease often will be low. Heritability of daughter calving ease is 5 percent, and is similar to traits such as somatic cell score and productive life. Reliabilities for daughter calving ease are lower than service-sire calving ease because of this lower heritability, and also because only females express daughter calving ease. In addition, more extensive pedigree information is required for evaluation. This means that parent average will be an important source of information for many newly released sires.

Daughter calving ease can be used as a general sire selection tool, and can be included in a selection index to improve overall calving performance or to prevent calving performance from getting worse.

Helps Identify Two Groups of Sires
The new calving-ease evaluations expose two groups of bulls that we wouldn't otherwise know about. First, the evaluations will identify bulls whose offspring are born with some difficulty, but develop into cows with good maternal ability. These sires can be used to breed mature cows and will help produce heifers that deliver calves easily. In addition, the new evaluations will identify bulls that sire easily born calves, but when the daughters mature, they are not as good at delivering calves. These sires should not be used widely in breeding heifers. They may help avoid calving problems in the short run, but may lead to difficulty when these calves become mature cows.

The new calving-ease evaluations will provide two values we can use in choosing A.I. sires. Service-sire calving-ease values should be used to determine which sires to use for breeding heifers. Daughter calving-ease values can be used as an overall selection tool. Use them cautiously, however, because daughter calving-ease values will have low reliability for many A.I. sires.

These new tools can be used to help improve calving performance in Holsteins.

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