Matings and litters were studied involving all three-breed crosses (sired by purebred boars) and four-breed crosses (sired by crossbred boars) from the Duroc, Yorkshire, Landrace and Spotted breeds. There were 764 female mating records and 161 boars used over five sequential breeding seasons. A sample of pregnant gilts was slaughtered each season and the remainder were allowed to carry their litters to term so that 493 litters resulted. Crossbred and purebred boars and crossbred females were evaluated for their contributions to conception rate (first service and over an 8-wk breeding season), number of services/ conception, litter size and weight at birth, 21 and 42 d and survival rate to 21 and 42 d. Crossbred boars had a 17.9% higher first service conception rate, a 5.3% higher breeding season conception rate and performed .11 fewer services/conception compared with purebred boars. There were no significant differences among the boar breeding groups for litter size, weight or survival rate. The six crossbred female groups (reciprocal crosses were combined) did not differ significantly in conception rate or number of services/ conception. There were significant differences in litter weight born and differences that approached significance (P\u3c.10) for litter size at 42 d and litter weight at 21 d. Yorkshire- Landrace females had the largest litters at birth, 21 and 42 d and the heaviest litters at 21 and 42 d. The smallest litters at 21 and 42 d were from Yorkshire-Spotted females, and they also had the lightest weight litters at all three stages.
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