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ANALYSIS OF NEBRASKA SWINE FIELD RECORDS: SELECTION PRACTICES AND GENETIC TRENDS
Abstract
Records from 101,606 hogs raised in 18 Nebraska Specific Pathogen Free herds collected during 1971 through 1979 were analyzed. Average selection differentials from 394 boars were -.83 mm for backfat adjusted to 100 kg(BF), 9.8 kg for weight adjusted to 140 days of age (WT), and -.1 pig for litter size alive at birth (NBA). Average selection differentials from 4844 gilts were -.30 mm for BF, 6.1 kg for WT and -.1 pig for NBA. Retrospective index techniques were used to evaluate relative selection emphasis on BF, WT and NBA. Most selection pressure was on WT for both male and female selection. There was some evidence that BF influenced selection of replacement sires. On the average NBA was ignored in the selection decision for boars and gilts. Standardized selection differentials of 1.23 for boars and .74 for gilts were observed for the retrospective index which included BF, WT and NBA. Offspring of introduced sires were similar to progenies from sires selected from within the herd. Averaged across herds, the difference of within herd sires' progeny for introduced sires' progeny was .0 mm for BF and .2 kg for WT. Approximately half of the pigs in this data set were sired by purchased boars. Estimates of the heritability of BF and WT were obtained by quadrupling the intraclass correlation between paternal half-sibs. Calculations were done within-herd and within-sex. Weighting each estimate by the inverse of its variance yielded an average heritability for BF of .07 (+OR-) .011 and average heritability for WT of .08 (+OR-) .009. An estimate of the genetic correlation between BF and WT of -.09 (+OR-) .001 was obtained from sire components of variance and covariance. Estimates of the phenotypic correlation between BF and WT were generally small and negative. Phenotypic trends for BF were favorable in most herds. WT was decreasing, phenotypically, in as many herds as it was increasing. Significant genetic trends in BF were detected only in estimates from females in four herds. One of these was in the undesirable direction. The genetic trend for BF, averaged across herds and sexes, was near zero. The corresponding value for WT was .6 kg per year. The expected genetic change from within-herd selection was estimated using selection applied to a retrospective index of BF and WT and the heritability and genetic correlation estimates obtained. This resulted in an average prediction of no change in BF and a .8 kg per year change in WT.
Subject Area
Livestock
Recommended Citation
DAVID, PHILLIP JAMES, "ANALYSIS OF NEBRASKA SWINE FIELD RECORDS: SELECTION PRACTICES AND GENETIC TRENDS" (1981). ETD collection for University of Nebraska-Lincoln. AAI8203212.
https://digitalcommons.unl.edu/dissertations/AAI8203212