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Abstract
The use of genomic information increases the accuracy and persistence of predictions, and decreases the generation interval, speeding up genetic changes in populations. Intensive changes caused by selection can reduce genetic variation and can strengthen undesirable genetic correlations. Stability of genomic predictions is high for proven animals or animals without new data when ample amount of pedigree, phenotypic and genomic data is available to estimate accurately the value of nearly all the independent chromosome segments segregating in the population. The objective of this dissertation was to investigate changes in genetic parameters, stability, and decay of genomic predictions over time in populations under genomic selection. Datasets from pigs, beef cattle and broilers were used. Genetic parameters for fitness and growth traits were estimated by Gibbs sampling in a pig population. Over 10 years, heritabilities for fitness and growth traits decreased ~25 and ~50%, respectively. Genetic correlations between fitness and growth traits that were initially positive remained stable, while those that were initially negative became more negative. Stability of predictions was evaluated during 1 year in a beef cattle population contrasting monthly evaluations of estimated breeding values (EBV) and genomic EBV for genotyped animals with or without their own phenotypes or progeny phenotypes. Average absolute changes for EBV were about two times smaller than for GEBV, except for animals with new progeny phenotypes (≤0.12 and ≤0.11 additive genetic standard deviations (SDa) for EBV and GEBV). The maximum absolute changes for EBV (≤2.95 SDa) were greater than for GEBV (≤1.59 SDa). Decay of genomic predictions was assessed in a broiler population across 7 years in the progeny, grand progeny, and great grand progeny. The use of genomic data increased accuracy and persistence of genomic predictions about two-fold compared to traditional evaluation. Accuracy of genomic predictions declined over generations, on average, 40% from progeny to grand progeny and 4% from grand progeny to great grand progeny. Strong selection reduced heritabilities and emphasized the antagonistic genetic relationships between fitness and growth traits. Genomic predictions are as stable as traditional evaluations for animals with new phenotypic data and with less extreme changes because of increased accuracy.