Different Lactations for Estimating Genetic Merit of Dairy Cows

Abstract

Heritabilities for milk and fat production of Holstein cows were highest at 0.35 and 0.33 for 1st lactation and decreased to 0.21 and 0.20 for 5th lactation. Genetic correlations between consecutive lactations were above 0.9, except for 0.75 between 1st and 2nd, and decreased as lactations were farther apart. Relationships between production by cows and their daughters were higher when both animals were in the same herd than when they were in different herds. The cow lactation most valuable in predicting a daughter lactation was generally the 1 with the same number; this suggests that production in different lactations is controlled by different genes. The 3rd lactation of a cow was most highly related to lifetime production of the daughter. First lactation was not as useful in estimating genetic merit as is accepted. The results provide little support for weighting lactations differentially for sequence.