Factors Affecting Age at First Parturition, Life Span, and Vital Statistics of Florida Dairy Cows

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Abstract
Data from seven herds representing 14 to 52 yr were examined with 2937 to 4651 observations for various analyses. Mean age at first parturition was 29.2 mo with heritability .16 and no trend over years. First parturition age was negatively correlated (-.05) phenotypically with productive life span (time from first to last parturition), total life span (-.05), and number of parturitions (-.06). The latter were highly correlated with each other, .86 to .97. Mean productive life span was 37.3 mo. total life span 70.0 mo, and number of parturitions 3.4. Mastitis and under troubles were more apparent with Holsteins (51%) than Jerseys and Geurnseys (22%), as were losses due to problems at parturition (4.8 versus 2.6 and 3.6%). Farm and breed effects were detected for nearly all variables, as were their interactions. Cause of such interactions remains unknown. Based on life tables, after first parturition Jerseys had longest predicted productive life span (61.1 mo), followed by Guernseys (57.4) and Holsteins (56.2). Frequency of culling for low milk yeild increase over the years studied, but losses due to mastitis and udder troubles, reproductive failure, and calving difficulty remained essentially unchanged.