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Animal Breeding and Genetics
Asian-Australasian Journal of Animal Sciences 2001;14(7): 910-914.
DOI: https://doi.org/10.5713/ajas.2001.910    Published online July 1, 2001.
Genetic Parameter Estimation with Normal and Poisson Error Mixed Models for Teat Number of Swine
C. Lee, C. D. Wang
The teat number of a sow plays an important role for weaning pigs and has been utilized in selection of swine breeding stock. Various linear models have been employed for genetic analyses of teat number although the teat number can be considered as a count trait. Theoretically, Poisson error mixed models are more appropriate for count traits than Normal error mixed models. In this study, the two models were compared by analyzing data simulated with Poisson error. Considering the mean square errors and correlation coefficients between observed and fitted values, the Poisson generalized linear mixed model (PGLMM) fit the data better than the Normal error mixed model. Also these two models were applied to analyzing teat numbers in four breeds of swine (Landrace, Yorkshire, crossbred of Landrace and Yorkshire, crossbred of Landrace, Yorkshire, and Chinese indigenous Min pig) collected in China. However, when analyzed with the field data, the Normal error mixed model, on the contrary, fit better for all the breeds than the PGLMM. The results from both simulated and field data indicate that teat numbers of swine might not have variance equal to mean and thus not have a Poisson distribution.
Keywords: Hierarchical Likelihood; Nonlinear Model; Variance Components
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