RESTRICTED MAXIMUM-LIKELIHOOD-ESTIMATION OF VARIANCE-COMPONENTS FROM FIELD DATA FOR NUMBER OF PIGS BORN ALIVE

Variance components for number of pigs born alive (NBA) were estimated from sow productivity field records collected by purebred breed assoc iations. Data sets analyzed were as follows: Hampshire (n = 13,537), L andrace (n = 10,822), and Spotted (n = 3,949). Variance components for service sire, sire of sow, dam of sow, and residual effects on NBA (a djusted for parity) were estimated. The single-trait model included re lationships between service sires, sires of sows, and dams of sows. Th e model was implemented using an expectation maximization (EM) REML al gorithm. A sparse-matrix solver was also used. Heritability estimates for NBA were .13, .13, and .12 for Hampshire, Spotted, and Landrace, r espectively. Estimates of maternal genetic (co)variances (m2) expresse d as a proportion of the phenotypic variance were .05, .01, and .03 fo r Hampshire, Spotted, and Landrace, respectively. Results indicated th at service sires account for 1 to 2% of the total variation for NBA. G enetic effects influencing NBA seem to be small in these data sets, bu t selection for increased NBA should be effective.