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Selection for Increased Leanness of Yorkshire Swine. II. Population Parameters, Inbreeding Effects and Response to Selection¹

Ohio Agricultural Research and Development Center, Wooster 44691

Abstract

An experiment to evaluate alternative techniques of selection for increased leanness of Yorkshire swine provided data suitable for the study of population parameters, inbreeding effects and response to selection. Two measures of leanness were defined as percentage lean cuts at 81.6 kg live weight (PCLC) and weight of lean cuts at 160 days of age (WLC). Select lines were established for each trait in addition to a contemporary control.

Individual inbreeding decreased WLC (–.14±.06 kg/%) but did not significantly affect PCLC (–.03±.02%/%). Effects of inbreeding of dam on the primary traits were significantly different among lines. Progeny performance was improved by increased inbreeding of dam in the select lines, whereas higher levels of inbreeding of dam decreased performance in the control line. The estimated effects of inbreeding of individual and dam on performance were substantiated by noting the tendency for selected parents to be less inbred and out of dams more inbred than average.

The responses to selection were estimated by regression of generation means adjusted for environmental effects on generation number. Direct selection for WLC provided an increase of .50±.19 kg per generation and a correlated PCLC response of .23±.09 % per generation. Response to direct selection for PCLC was .38±.10% per generation, while indirect selection for WLC was ineffective (–.05±.21 kg per generation). A technique for estimation of realized heritability when combined family and individual selection has been applied is presented. Realized heritability estimates corrected to a non-inbred population basis were 17.4% for WLC and 32.5% for PCLC. The corresponding paternal half-sib estimates were .20±.06 and .44±.10, respectively.

¹ Published with approval of the Director as Paper No. 88-78, Journal Series, the Ohio Agricultural Research and Development Center.

² Present address: U.S. Meat Animal Research Center, Agricultural Research, SEA, Clay Center, NE 68933.

³ Animal Science Department, The Ohio State University, Columbus 43210.