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Models with nuclear, cytoplasmic, and environmental effects for production traits of Columbia sheep¹

K. J. Hanford, G. D. Snowder and L. D. Van Vleck^,2

USDA, ARS, U.S. Meat Animal Research Center, Lincoln, NE 68583-0908 and and Clay Center, NE 68933

² Correspondence: A218 Animal Sciences, University of Nebraska, Lincoln 68583-0908 (phone: 402-472-6010; fax: 402-472-6362; E-mail: lvanvleck{at}unlnotes.unl.edu).

Statistical models (16) were compared for birth weight of 24,741 Columbia lambs recorded at the U.S. Sheep Experiment Station (USSES; 1950 to 1998). The goal was to estimate fractions of variance due to cytoplasmic line (c²; n = 590) and sire x cytoplasmic line interaction (sc²; n = 12,831) with other nuclear and environmental effects included in the model. The basic model included direct genetic (fractional variance, a²; n = 26,623), maternal genetic (m², with direct-maternal correlation r_am), and maternal permanent environmental (; n = 6,385) effects. The model with sc² was significantly (P < 0.05) better than the basic model with c², but with other random effects added, sc² became zero. Significant (P < 0.05) variance components were associated with random dam x year (dy²) and dam x number born (dn²) interaction effects. Estimates with all effects in the model were: a², 0.26; m², 0.24; r_am, -0.05; , 0.02; c², 0.00; dn², 0.04; dy², 0.08; sd², 0.04; sc², 0.00. Estimates for a², m², and r_am were the same for all models. Estimate of changed when other effects were added to the model. The largest estimates for nongenetic effects were: , 0.06; c², 0.00; dy², 0.14; sd², 0.13; and sc², 0.04. Parameter estimates were similar regardless of whether fixed genetic groups (n = 84) were in the model. For weaning weight (120 d, n = 23,903), estimates of variances of effects added to the basic model were all near zero (a², 0.14; m², 0.09; r_am, 0.23; , 0.04). For fleece weight (FW, n = 29,024) and number born (NB, n = 29,688), animal permanent environmental effects were added to the model (; n = 7,741 and 7,840) and r_am was dropped. For these traits, effects not in the basic model had small variances. For FW, estimates with the full model were: a², 0.52; m², 0.01; , 0.00; , 0.06; c², 0.00; dy², 0.00; sd², 0.02; and sc², 0.06, and for NB they were: a², 0.08; m², 0.00; , 0.00; , 0.02; c², 0.00; dy², 0.00; sd², 0.00; and sc², 0.01. Cytoplasmic effects were not important. Unusual random effects in the model did not change estimates for basic parameters. Although some effects were significant, especially for BW, effects on genetic evaluations are likely to be small.

Key Words: Cytoplasmic Inheritance • Genetic-Environment Interaction • Genetic Variation • Heritability

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