Materials and Methods
Data
A total of 724 purebred Large White and Yorkshire and reciprocally crossed boars and gilts were included in the study. The research animals were a representative of a closed herd developed in 1992 and were raised in accordance with approved farm management practices at the Western Branch of the Ohio Agricultural Research and Development Center. All animals were genotyped at the ESR locus via a PCR-RFLP (PvuII) procedure previously described by Short et al. (1997) or by pedigree analysis in which both parents were homozygous. The ESR allele and genotype frequencies were calculated in the purebred populations and allele frequencies were used to determine the expected genotype frequencies assuming Hardy-Weinberg equilibrium. Traits measured included TN, IBW, WW, AGE, ADG, BF, and LMA. The TN and IBW were measured immediately post-partum. TN was recorded as the sum of all teats and was measured on gilts only. Weaning weight was recorded at approximately 21 days of age. Animals were placed on test by pen at approximately 75 lb and were weighed every two weeks. Animals remained on test until the pen average was approximately 240 lb. The ADG was recorded as the individual's on-test weight gain divided by the number of days on test. At the end of the test period backfat thickness and loin-muscle area were measured by a certified ultrasound technician at the 10th rib two inches off the midline using a B-mode (Real-Time) ultrasound machine.