CARCASS AND RELATED TRAITS IN DUROC AND YORKSHIRE PIGS SELECTED FOR SOW PRODUCTIVITY AND PIG PERFORMANCE 1

Summary Main and interaction effects of breed, line, sex and season on 15 carcass and two related performance traits were evaluated in 649 Duroc and Yorkshire pigs. Selection of replacement animals in spring litters was based on an index of sow productivity and in fall litters on an index of average daily gain, scan backfat and loin eye area. Control lines were also maintained in each breed in each season. Five generations of selection were represented in spring pigs and three generations in fall pigs. Various statistical models were used to test interaction effects. Breed x fall select vs control lines was the only interaction that was significant for more than one or two traits. A reversal in order of the least-squares means for the select and control lines between the two breeds resulted in the significant interaction effects in eight of nine carcass traits. The Duroc select line was leaner than the Duroc control line but the reverse was generally true for Yorkshires. In main effects, Durocs were generally leaner than Yorkshires and gilts were leaner than barrows. Durocs also exceeded Yorkshires in both gross and lean cuts average daily gain, and barrows were higher than gilts in both traits. Partial regressions of tratis on years suggested possible negative corre- lated responses to the selection for sow produc- tivity practiced among spring pigs. Residual