Reproductive Performance from Daughters of Single and Multiple Trait Selected Sires

Abstract

Sires selected for milk in first lactation (Yield) and those selected for udder conformation, percentage of daughters culled in first lactation, and fat-corrected milk (Merit) were mated randomly to cows in the Beltsville herd. Subsequent offspring were mated to bulls from the same selection group as their sires. Reproductive traits were numbers of heats and services, age at first heat, gestation length, and age at first calving for heifers and numbers of heats and services, gestation length, days to first heat postpartum, and calving interval for cows. Selection groups differed only for gestation length with Merit females having a 2 day longer gestation than Yield females. Yield females calved earlier (12 days) and had shorter calving intervals (14 days) than Merit females.Mating bull was significant for gestation length and for percent pregnant on a given service but not on first or first four services. Selection groups differed in gestation length only. Variance components for mating bulls for all traits and for sire of cow for gestation length were all less than 10% with most less than 3%.Reproductive performance of offspring from selection of bulls solely for milk in first lactation was not inferior to that of offspring of bulls selected less intensely for milk. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. ABSTRACTSires selected for milk in first lactation (Yield) and those selected for udder conformation, percentage of daughters culled in first lactation, and fat-corrected milk (Merit) were mated randomly to cows in the Beltsville herd. Subsequent offspring were mated to bulls from the same selection group as their sires. Reproductive traits were numbers of heats and services, age at first heat, gestation length, and age at first calving for heifers and numbers of heats and services, gestation length, days to first heat postpartum, and calving interval for cows. Selection groups differed only for gestation length with Merit females having a 2 day longer gestation than Yield females. Yield females calved earlier (12 days) and had shorter calving intervals (14 days) than Merit females.Mating bull was significant for gestation length and for percent pregnant on a given service but not on first or first four services. Selection groups differed in gestation length only. Variance components for mating bulls for all traits and for sire of cow for gestation length were all less than 10% with most less than 3%.Reproductive performance of offspring from selection of bulls solely for milk in first lactation was not inferior to that of

Genetic relationship of yield and fertility in dairy cattle

“…Analyzing the NC-2 project at the Beltsville Agricultural Research Center, Rothschild et al (1981) concluded the reproductive performance of the high yield group was not inferior to the low yield group.…”