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Originally published as Genetics Published Articles Ahead of Print on November 3, 2008.

Genetics, Vol. 181, 277-287, January 2009, Copyright © 2009
doi:10.1534/genetics.108.094888

Exploring Biological Relationships Between Calving Traits in Primiparous Cattle with a Bayesian Recursive Model

Evangelina López de Maturana*,1, Xiao-Lin Wu{dagger}, Daniel Gianola*,{dagger},{ddagger}, Kent A. Weigel{dagger} and Guilherme J. M. Rosa{dagger}

* Department of Animal Sciences, {dagger} Department of Dairy Science and {ddagger} Department of Biostatistics and Medical Informatics, University of Wisconsin, Madison, Wisconsin 53706

1 Corresponding author: Departmento de Mejora Genética Animal, INIA, Crta. de la Coruña, km 7.5, 28040 Madrid, Spain.
E-mail: ldematurana.eva{at}inia.es

Structural equation models (SEMs) of a recursive type with heterogeneous structural coefficients were used to explore biological relationships between gestation length (GL), calving difficulty (CD), and perinatal mortality, also known as stillbirth (SB), in cattle, with the last two traits having categorical expression. An acyclic model was assumed, where recursive effects existed from the GL phenotype to the liabilities (latent variables) to CD and SB and from the liability to CD to that of SB considering four periods regarding GL. The data contained GL, CD, and SB records from 90,393 primiparous cows, sired by 1122 bulls, distributed over 935 herd-calving year classes. Low genetic correlations between GL and the other calving traits were found, whereas the liabilities to CD and SB were high and positively correlated, genetically. The model indicated that gestations of ~274 days of length (3 days shorter than the average) would lead to the lowest CD and SB and confirmed the existence of an intermediate optimum of GL with respect to these traits.