SummaryRecords collected during 1971 through 1979 from 101,606 hogs raised in 18 Nebraska Specific Pathogen Free herds were analyzed. Traits considered were backfat at 100 kg (BF), weight at 140 d of age (WT) and, in some analyses, number of live pigs/litter at birth (NBA). The phenotypic correlation of BF and WT, averaged across herds, was -.07. The correlations between BF and NBA and between WT and NBA were .04 and -.05, respectively. Average phenotypic standard deviations for BF, WT and NBA were 2.6 mm, 8.8 kg and 2.0 pigs. Estimates of the heritability of BF and WT were lower than most estimates reported from university research herds. Within breed, herd and sex estimates of heritability ranged from -.22.and .51 (unweighted X, = .16 -+ .025) for BF and ranged from -.28 to .49 (X = .16 + .016) for WT. Estimates of the genetic correlation between BF and WT were extremely variable (X = -.62 + 14.3, range = -9.42 to 1.30) among breed-herd-sex subclasses.

Best linear unbiased predictions (BLUP) using information from all known relatives; selection index using phenotype, full-sib average and half-sib average; and phenotypie deviation from contemporary group average were compared as methods of predicting breeding values for days to 100 kg and backfat. Swine records (n = 203,869) from five Hampshire, one Duroc and six Yorkshire herds were obtained from the Nebraska SPF Swine Accrediting Agency. Heritability values used to compute BLUP or index were either estimates based on within-breed offspring on parent regression or values recommended by the National Swine Improvement Federation (NSIF) guidelines. Within-breed estimates of heritability ranged from .11 to .25 for days to 100 kg and from .10 to .22 for backfat. Heritabilities recommended by NSIF were .35 for days to 100 kg and .40 for backfat. Correlations between index and phenotypic deviation were larger than correlations between BLUP and phenotypic deviation or BLUP and index. Correlations between BLUP and index were slightly larger than correlations between BLUP and phenotypic deviation. Increasing the heritability values used to compute BLUP or index increased the correlations among methods. Value of heritability had little effect on the correlation between a parent's predicted breeding value and its progeny average. On the average and assuming the NSIF heritability, the correlation between BLUP of a sire and its progeny average was 33% larger for days to 100 kg and 44% larger for backfat than the correlation between the phenotypic deviation of a sire and its progeny average. The advantage of BLUP over phenotypic deviation for dams was less than for sires: 25% for days to 100 kg and 18% for backfat. Selection of pigs using BLUP instead of phenotypic deviation or index would substantially improve response to selection.

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Records collected during 1971 through 1979 from 101,606 pigs raised in 18 herds that were members of the Nebraska SPF Swine Accrediting Association were evaluated for phenotypic trends and predicted and observed genetic trends. Traits considered were backfat at 100 kg (BF) and weight at 140 d of age (WT). Phenotypic change on average was beneficial for BF (-.05 mm/yr) but undesirable for WT (-.2 kg/yr). However, the average observed genetic trend was nil for BF and .6 kg/yr for WT. An average, predicted response based on observed selection differentials and estimates of within herd-sex genetic parameters was in good agreement with observed response for BF, but was three times higher for WT.