title: An analysis of age and body weight at first calving for Holsteins in the United States.
abstract: In a national survey of US dairy producers, only 2.7 +/- 0.5% of Holstein dairy operations reported achieving recommended target ranges of age < or = 24 months and body weight (BW) > or = 550 kg at first calving. Allowing for wider target ranges, still only 14.6 +/- 1.3% of Holstein dairy operations reported achieving age < or = 25 months and BW > or = 544.3 kg at first calving. Ages of individual first-calf heifers observed at calving were heavily skewed toward older individuals. Dairy producers reported an average age at first calving that was 1.3 months lower than the mean and 1.0 months lower than median age of first-calf heifers' observed calving on the operations. Stepwise logistic regression was used to identify the herd characteristics associated with producers reporting first calvings within the wider age and BW target ranges for Holsteins. Rolling herd average milk production > or = 7711 kg/yr, using a computer for recordkeeping, and not tying preweaned heifers in a barn with cows, were associated with achieving the target BW and age at first calving.
authors.affiliation: United States Department of Agriculture, Centers for Epidemiology and Animal Health, Fort Collins, CO 80521, USA. wlosinger@aphis.usda.gov
authors.forename: W C
authors.initials: WC
authors.lastname: Losinger
authors.forename: A J
authors.initials: AJ
authors.lastname: Heinrichs
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D001835:Body Weight / Q000502:physiology*; D002417:Cattle / Q000502:physiology*; D003625:Data Collection; D005260:Female; D007743:Labor, Obstetric / Q000502:physiology*; D007774:Lactation / Q000502:physiology; D016014:Linear Models; D015233:Models, Statistical; D011247:Pregnancy; D012098:Reproduction / Q000502:physiology; D011795:Surveys and Questionnaires; D014481:United States