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Short Communication: Validation of Two Animal Models for Estimation of Genetic Trends for Female Fertility in Norwegian Dairy Cattle

I. M. Andersen-Ranberg^*,, G. Klemetsdal^* and B. Heringstad^*

^* Department of Animal Science, Agricultural University of Norway, N-1432 Ås, Norway and
GENO Breeding and A.I. Association, N-1432 Ås, Norway

Corresponding author: I. M. Andersen-Ranberg; e-mail: ina.ranberg{at}ihf.nlh.no.

Two animal models were compared with respect to potential bias in genetic trend estimates for female fertility and for their predictive ability. In addition to either a fixed effect for month of first insemination or for month-year of first insemination, the models had fixed effects of age and double insemination and random effects of herd-year and animal. The model with a fixed effect of month of first insemination had a larger positive genetic trend for 56-d nonreturn rate in virgin heifers (0.16% yr), smaller downward bias, and somewhat higher predictive ability. These results demonstrate the importance of verifying models to be used in the calculation of breeding values.

Key Words: female fertility • genetic trend • model validation

Abbreviation key: NRF = Norwegian dairy cattle, NR56D0 = 56-d nonreturn rate in virgin heifers

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