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Title: Potential Consequences Of Selection On Gestation Length On Holstein Performance

Author
item Norman, H
item Wright, Janice
item MILLER, R - Retired ARS Employee

Submitted to: World Congress of Genetics Applied in Livestock Production
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2010
Publication Date: 8/1/2010
Citation: Norman, H.D., Wright, J.R., Miller, R.H. 2010. Potential Consequences Of Selection On Gestation Length On Holstein Performance. World Congress of Genetics Applied in Livestock Production. Proc. 9th World Congr. Genet. Appl. Livest. Prod., Leipzig, Germany, Aug. 1–6, 4 pp.

Interpretive Summary: Genetic evaluations of Holstein gestation length (GL) were analyzed to determine their reliability and repeatability. Potential consequences of selection on GL were assessed by examining impact on performance in the subsequent lactation. Service-sire predicted transmitting ability (PTA) for GL was effective in identifying bulls that could be expected to modify GL. Intermediate service-sire PTA GL was optimal for yield traits and days open; performance for productive life, calving ease, stillbirth and culling generally became less favorable as service-sire PTA GL increased. Based on phenotypic cow GL, performance generally improved for subsequent lactation yield as GL increased; intermediate GL was optimal for productive life, calving ease, stillbirth, culling and days open. Changing Holstein GL by more than a day or two would have limited benefit for overall performance.

Technical Abstract: The objective of this paper was to determine if genetic evaluations of Holstein gestation length (GL) were reliable and to assess potential consequences of selection for either shorter or longer GL by examining impact on performance in the subsequent lactation. Holstein bulls used to develop predicted transmitting ability (PTA) for GL were stratified into 7 groups by PTA for service-sire GL based on calvings from 1998 through 2005. An independent set of 261,598 first-parity cows mated to the same bulls and calving from 2006 through November 2009 were grouped by the service-sire PTA GL groups. Cow GL were examined to determine predictive effectiveness of previous service-sire PTA GL as well as the impact that differing GL had on phenotypic performance in the subsequent lactation. The model to analyze effectiveness of service-sire PTA GL included fixed effects for herd-year and service-sire PTA GL group (SS) as well as covariates for conception date (CD) and CD2 to eliminate differences in time opportunity among mates. Analyzed traits included GL; standardized milk, fat and protein yields; somatic cell score; productive life; days open; calving ease score (1 to 5, where 1 is no difficulty and 5 is extreme difficulty); stillbirth incidence (yes or no) and culling incidence (yes or no). Least squares means were calculated by service-sire PTA GL groups for the independent dataset. Results confirmed that Holstein GL can be changed through the choice of service sire. Herd managers could take advantage of this knowledge to aid in controlling calving season or predicting calving date. Relationship between GL and subsequent performance for three yield and six fitness traits were generally small (but real) for most traits. Changing Holstein GL by more than a day or two would have limited benefit for overall performance.