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University of Guelph2, Guelph, Ontario, Canada N1G 2W1
Abstract
Performance test records for age and backfat to 90 kg on 81,902 pigs (38,465 Yorkshire; 28,145 Landrace; 8,005 Duroc and 7,287 Hampshire) in 178 Ontario herds were analyzed within breed using maximum likelihood procedures. Between litter variances were large and indicated substantial maternal or common environmental effects, particularly for age to 90 kg. Males (intact) took 2.5 to 5.8 fewer days to reach 90 kg and had .84 to 1.64 mm less backfat than females. Females were considerably more variable than males for backfat. Multiplicative adjustments reduced, but did not eliminate, differences between the sexes for variability in backfat. Estimated annual trends in average sire and dam transmitting abilities for age to 90 kg were positive (.1 to 1.0 d/yr) and indicated that some genetic loss in growth rate had occurred. Trends in average sire transmitting abilities for backfat were small (–.02 to .04 mm/yr), and not significant, but there were sizable and significant reductions in average dam transmitting abilities (–.10 to –.21 mm/yr). Selection differentials for age to 90 kg were from –1.0 to –6.1 d for sires and –1.3 to –3.4 d for dams. Selection differentials for backfat were –.92 to –1.57 mm for sires and –.64 to –1.25 mm for dams. Standardized selection differentials were considerably greater for backfat than for age to 90 kg in both sires and dams.
1 Financial support was provided by the Ontario Pork Producers' Marketing Board and the Ontario Ministry of Agriculture and Food. Data were provided by the Animal Production Division of Agriculture Canada.
2 Dept. of Anim. and Poul. Sci.
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