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ARS Home » Research » Publications at this Location » Publication #233588
Title: A National Sire Fertility Index

Author
item Norman, H
item Hutchison, Jana
item Wright, Janice
item Hubbard, Suzanne

Submitted to: Dairy Cattle Reproduction Council Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/16/2008
Publication Date: 11/7/2008
Citation: Norman, H.D., Hutchison, J.L., Wright, J.R., Hubbard, S.M. 2008. A national sire fertility index. Dairy Cattle Reproduction Council Proceedings. Omaha, NE, Nov. 7-8, pp. 45-52.

Interpretive Summary: Today’s artificial-insemination organizations and dairy farmers want reliable information on the fertility of marketed bulls. In May 2006, USDA’s Animal Improvement Programs Laboratory assumed the responsibility for producing evaluations for bull fertility. An intense research investigation led to a new procedure called “sire conception rate” (SCR), which was implemented in August 2008. Two approaches were used in developing SCR evaluations. First, factors were identified that were related to the bull that provided the unit of semen and that could help to improve the prediction of whether that unit of semen resulted in a pregnancy. Second, factors were identified that were related to the cow receiving the unit of semen and that could distort the fertility measure for the bull providing the semen (nuisance variables); those nuisance variables were accounted for to produce the best predictor of the bull's true capability for impregnating cows. The new SCR evaluation is based on confirmed pregnancies and measures phenotypic service-sire fertility. It is expressed as a relative conception rate (an average bull has an SCR of 0.0%). The new SCR evaluation is more accurate than the previous method for measuring bull fertility because of its complex statistical model and a large increase in insemination information.

Technical Abstract: In May 2006, USDA’s Animal Improvement Programs Laboratory assumed the responsibility for producing evaluations for bull fertility. An intense research investigation led to a new procedure called “sire conception rate” (SCR), which was implemented in August 2008. Two approaches were used in developing SCR evaluations. First, factors were identified that were related to the bull that provided the unit of semen and that could help to improve the prediction of whether that unit of semen resulted in a pregnancy. Second, factors were identified that were related to the cow receiving the unit of semen and that could distort the fertility measure for the bull providing the semen (nuisance variables); those nuisance variables were accounted for to produce the best predictor of the bull's true capability for impregnating cows. The statistical model includes categorical fixed effects for individual parities for lactations 1 to 5, state-year-month of insemination group; 6 standardized milk yield groups, service number for inseminations 1 to 7, cow age, rounded to the nearest year, and herd-year-season-parity-registry status class; linear-regression covariate effects for service-sire and mating inbreeding coefficients; and random effects for service-sire age group, artificial-insemination (AI) organization-insemination year group; individual service sire; cow’s genetic ability to conceive; cow’s permanent environmental effect; and residual. Variances are 0.00014 for service-sire age group, 0.00011 for AI organization-insemination year group, 0.00054 for service sire, 0.00294 for cow, 0.00533 for cow’s permanent environment, and 0.196970 for the residual. To evaluate the impact of each individual effect in the model, alternative evaluations were calculated by sequentially removing the individual effect for service-sire or mating inbreeding, service-sire age group, or AI organization-insemination year group from the full model. The alternative models also were used to generate Holstein SCR evaluations based only on data prior to July 2006 to determine how effective each model was in predicting later data (July 2006 through January 2008). Among selection methods, prediction of future conception rate was improved most by including the 2 most recent AI organization-years and assigning a weight of 60% to the most recent year and 40% to the previous year. The new SCR evaluation is based on confirmed pregnancies and measures phenotypic service-sire fertility. It is expressed as a relative conception rate (an average bull has an SCR of 0.0%). The standard deviation of SCR evaluations was 2.37% in August 2008. An additional study was completed to determine the relationship between bull SCR and the fertility level of herds for which the bull was service sire. Herd conception rates were 22% superior for high-SCR bulls than for low-SCR bulls in low-fertility herds; corresponding superiorities for medium- and high-fertility herds were 18 and 17%, respectively. The new SCR evaluation is more accurate than the previous method for measuring bull fertility because of its complex statistical model and a large increase in insemination information. An 80% confidence-interval table is being developed for SCR evaluations to clarify differences among bulls.