Time trends, sex and age of dam correction factors, and genetic parameters for production traits in

herds were analyzed by least squares analysis. Herd, year, year within herd, sire within year within herd, sex, age of dam and interactions among these factors along with partial regressions on day of birth and age at weaning were included in various combinations as independent variables in three basic least squares models. Response variables were birth weight, pre- and postweaning average daily gains, weaning and final test weights. The objectives of the study were to analyze time trends, to calculate and evaluate sex and age of dam correction factors, and to estimate genetic parameters. Time trend analyses showed that birth and weaning weights increased significantly in the time period (1959 to 1973) of the study. There was a nonsignificant increase in postweaning gain and no change in final test weight. Correction factor analyses showed that multiplicative factors were generally preferred over additive in the Angus data except for the age of dam corrections for preweaning gain and weaning weight, where no decision was reached. In the Hereford data, multiplicative factors were preferred in both birth weight adjustments and in weaning weight age of dam adjustments. Additive factors were preferred in both Hereford preweaning gain adjustments and in weaning weight age of dam adjustments. Decision criteria for additive vs. multiplicative correction factors were the factors ' ability to affect major sources of variance, interactions, and individual sex and age of dam subclass variances. Estimates o