Genetic Parameters for Gestatiob Length, Birth Date and Time to First Observed Estrus Ib Beef Cattle

SUHMARY Genetic and evironmental variability in gestation length (GL), birth date (BD), and time from first day of breeding season to first observed estrus (FE) were analyzed ·using twelve years of breeding and calving records on cows, sired by Simmental, Maine-Anjou, Limous,in and Gelbvieh bulls. All cows were artificially inseminated. Statistical analyses were performed separately on first, second and last parity records. Paternal half-sib estimates of heritability for GL as a trait of the calf were between .36 and .45 while the estimates for BD were between .09 and .24. The estimates of heritability for FE, treated as a trait of the cow, were less than .10. Heritabilities for maternal additive effects were small for GL and BD. The correlation between direct and maternal additive eUects were negative for GL and BD in parity 1 and for GL in parity 2. The expected annua I responses to selection on an index that maximizes the sum of the direct and maternal breeding values were .76 d and 1.03 d for BD and GL, respectively .