Genetic and Phenotypic Parameters Estimated From Nebraska Specific-Pathogen-Free Swine Field Records

Abstract

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.

Comparison of Methods of Predicting Breeding Values of Swine

“…Therefore, the discrepancy between estimates of heritability from the current study and the values recommended by NSIF cannot be explained solely by bias due to selection of progeny. David et al (1983) suggested that the low estimates of heritability that they obtained from some of the same data compared to results from experiments might be due to more heterogeneous environments for SPF pigs compared to pigs from experiments. Another explanation is that contemporary groups probably are less correctly specified in private seedstock herds than in experimental herds.…”

“…Estimates of heritability in the literature vary widely (Hutchens and Hintz, 1981;David et al, 1983;Kennedy et al, 1985;Bereskin, 1987). In spite of this, the general conclusion of swine geneticists is that h 2 is near .35 for days to 104.4 kg and .40 for backfat as indicated by the National Swine Improvement Federation (NSIF) guidelines (1987).…”

“…In the face of uncertainty about whether or not truncation selection on the phenotype occurred, we are assuming that it is more conservative to make the error of concluding that BLUP or index is the same as or worse than phenotype when in fact it is better than it is to make the error of concluding that BLUP or index is better than phenotype when in fact it is not. This assumption is justified by the fact that the status quo in the U.S. swine seedstock industry is no selection (David et al, 1983) or selection on phenotype or indices that utilize information from other traits but not information from relatives.…”

“…Large piglets grow faster and are less likely to die than small piglets. Pigs that had backfat data were selected based on their growth rate (David et al, 1983). Growth rate has a small positive phenotypic correlation with backfat (Bereskin, 1987).…”

“…The traits considered were days to 100 kg and average backfat probe at 100 kg. Data and adjustment of data for pigs not weighing 100 kg when weighed were described in detail by David et al (1983). Analyses were done separately for each traitbreed combination.…”