Sustained Cow Fertility Evaluation

An American Hereford Association release is available from the Sustained Cow Fertility (SCF) genetic evaluation.  This trait is different than other reproductive and longevity traits. The novel analysis does an effective job of modelling contemporary groups to account for differences in females within groups that change over time due to culling.  The resulting genetic values from a sire model provide a new-generation selection tool available to cattle breeders.  More importantly this tool can be incorporated into existing AHA index values.

Highlights
The sustained cow fertility evaluation is conducted using software developed especially to implement genetic evaluation for time-to-event data (Mészáros. Sölkner and Ducrocq. Computer Methods and Programs in Biomedicine. 2013. 110(3): 503–510). For the sustained cow fertility genetic evaluation, the event of interest occurs when a female no longer calves annually after having calved as a two-year-old.  This survival analysis utilizes Whole-Herd TPR records in a sire evaluation model that includes extended pedigree for sires’ parents, resulting in over 63,000 breeding values.

The yearling contemporary group initiates the analysis.  Essentially the SCF dataset is an extension of the data edited for the Heifer Calving Rate genetic evaluation.  After the initial yearling group for SCF, dynamic contemporary groups thereafter are used where females exposed together make up a contemporary group.  Censoring of females as appropriate takes place to not penalize for certain lifetime events, such as young females, females sold, or females becoming donors.

The calculated age at calving each parity and inter-calving period are used to establish “Success”.  The success for a producing female in the herd continues each production cycle until the inter-calving period is less than gestation length, or dam produces an ET calf, or dam is transferred.  In addition, the analysis accounts for milk and total maternal calving ease EPDs.  Heritability for the current analysis was .20.  Estimates in cattle for other conceptually related traits ranged between .02 and .20 in the literature (MacNeil and Vukasinovic. J. Anim. Sci. 2011. 89:1712-1718)

The Sustained Cow Fertility (SCF) results, reported in percentage units, are oriented such that larger breeding values reflect sires whose daughters calve annually for more years.  For example, if Bull A has a SCF = 110 and Bull B has a SCF of +95, Sire A’s daughters are at 15% less risk of being open after a 60-day breeding season than Sire B’s daughters.

Example SCF (%)
Sire A: SCF         =    110%
Sire B: SCF         =      95%     
Difference      15%

Sire breeding values are associated with more success in future daughters remaining in the herd when SCF is above 100, and are associated with more risk (less success) when SCF values are below 100.

Prototype Evaluation Results
The Sustained Cow Fertility listing provided in the following download contains sires with a minimum of 10 daughters in the prototype genetic evaluation.  The average value for these sires was 98%.

>>> Download results

— American Hereford Association staff

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