|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 20, 2002
Publication Date: January 1, 2003
Citation: Van Vleck, L.D., Hanford, K.J., Snowder, G.D. 2003. Models with cytoplasmic effects for birth, weaning and fleece weights, and litter size at birth for a population of Targhee sheep. Journal of Animal Science. 81:61-67. Interpretive Summary: Cytoplasmic effects are transmitted directly from mother to progeny. Analyses with other species have sometimes found what appeared to be important effects associated with the original source of cytoplasm. This study of 33,994 Targhee lambs with records at the US Sheep Experiment Station since 1950 was to determine if cytoplasmic effects and effects of interactions of cytoplasmic origin and nuclear genotype were important for four representative traits: birth and weaning weight, litter size at birth and fleece weight. For all traits, no evidence for cytoplasmic effects was found. For birth weight, interaction effects of dam by year and dam by number born unexpectedly accounted for a significant amount of variation (but not for other traits). Those interactions, however, did not affect estimates of genetic parameters used in genetic evaluation systems ¿ direct and maternal heritability ¿ and therefore would not be expected to influence genetic evaluations very much. For the other traits, the models usually recommended for genetic evaluations seem appropriate. There seems to be no need to complicate national genetic evaluations by including cytoplasmic and genotype by cytoplasmic effects in the statistical models used for genetic evaluations.
Technical Abstract: Models (15) were compared for birth weight of 33,994 Targhee lambs recorded at USSES (1950-1998). Intent was to estimate fractions of variance due to cytoplasmic line (c2) and sire by cytoplasmic line interaction (sc2). Basic model included direct genetic (fractional variance, a2), maternal genetic (m2, with correlation r-am), and maternal permanent environmental (p2) effects. Model with sc2 was significantly better than basic model with and without c2. When other effects were added, sc2 became zero. Significant effects were associated with dam by year (dy2), sire by dam (sd2) and dam by number born (dn2) interaction effects. Estimates with all effects in model were: (a2, 0.24; m2, 0.19; r-am, 0.11; p2, 0.05; c2, 0.00; dn2, 0.04; dy2, 0.06; sd2, 0.05; sc2, 0.00). Estimates for a2, m2, and r-am were same for all models. Largest estimates for non-genetic effects were: p2, 0.08; c2, 0.00; dy2, 0.13; sd2, 0.11; and sc2, 0.04. For weaning weight, estimates for all of effects added to basic model were near zero (a2, 0.18; m2, 0.12; r-am, -0.01; p2, 0.06). For number born (NB) and fleece weight (FW), animal permanent environmental effects were added to the model (ap2) and r-am was dropped. For neither trait did any effects beyond the basic model have large variances. For NB, non-zero estimates with full model were: (a2, 0.10; ap2, 0.01; dy2, 0.02; sc2, 0.01) and for FW were: (a2, 0.54; m2, 0.02; ap2, 0.02; dy2, 0.04 and sc2, 0.02). For all traits, cytoplasmic effects were not important. Addition of unusual random effects to model did not change estimates for the basic parameters. Although some of these effects were significant for birth weight, the effect on genetic evaluations will be small.