Mt. See et al., RESTRICTED MAXIMUM-LIKELIHOOD-ESTIMATION OF VARIANCE-COMPONENTS FROM FIELD DATA FOR NUMBER OF PIGS BORN ALIVE, Journal of animal science, 71(11), 1993, pp. 2905-2909
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.