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Selection for Increased Leanness of Yorkshire Swine. I. Experimental Procedures and Selection Applied¹

Ohio Agricultural Research and Development Center, Wooster 44691

Abstract

The procedures utilized and selection applied were described for an experiment designed to evaluate alternative techniques of selection for increased leanness of Yorkshire swine. 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). These traits were estimated by utilization of ultrasonics on the potential breeding stock. Select lines were established for each trait in addition to a contemporary control. Selection within paternal half-sib families was based on a combined selection index utilizing individual and litter performance. Four generations of selection have been completed.

The conventional selection differential was partitioned into three component deviations measured as the deviation of individual phenotype from full-sib family mean (1), full-sib family mean from half-sib family mean (2) and half-sib family mean from line mean (3). The corresponding midparent weighted partitioned selection differentials per generation were 2.79, 1.68 and –.04 kg for the WLC line and .722, .511 and .127% for the PCLC line, respectively.

Unintentional positive selection in the control line was about 5% of direct selection in the WLC line and 20% of direct selection in the PCLC line, but for lower PCLC. The intentional selection of boars accounted for approximately 80% of the selection practiced in each select line. Extreme sires and dams of the WLC line produced more offspring than less extreme parents, while no consistent differences were observed in the PCLC line. As indicated by the index in retrospect technique, individual performance received slightly more attention, relative to litter performance, than was intended.

¹ Published with approval of the Director as Paper No. 77–78, 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.