title: Prepartum and peripartum reproductive performance of dairy heifers freshening at young ages.
abstract: Reproductive performance of five breeds (81% Holstein or Jersey) in the Florida Agricultural Experiment Station herd was evaluated from data collected over 20 yr. Data represented 1144 parturitions after gestations greater than 250 d with all twin births excluded. Number of services per conception was not affected by age at first insemination. Mean age of exposure to first service was 414 d; mean age at first parturition was 25.8 mo. Overall, 39.7% of heifers calved at 23 mo or less. Intermediate ages, 24 to 27 mo, comprised 33.9% of heifers, whereas 26.4% of heifers calved at greater than or equal to 28 mo. Overall incidences of problems at parturition were retained fetal membranes, 3.6%; dystocia, 3.8%; metritis, 10.5%; and stillbirth, 11.5%. Frequencies of stillbirth and retained fetal membranes apparently were not affected by age, but metritis increased linearly with age at first parturition. Holsteins experience higher incidences of all problems than did Jerseys. Heritability (from paternal half-sib correlation) of birth weights and gestation lengths were .31 and .24; genetic correlation was .14. Heritabilities of occurrence of stillbirth, retained fetal membranes, metritis, and dystocia were negative and considered to be 0. Heritabilities of age at first service, days from first service to conception, number of services, and age at first parturition were .22, .11, .05, and .43. Dairy producers can consider reducing age at first parturition to at least 22 mo, under environmental and management conditions of this study, without increased frequencies of problems at parturition.
authors.affiliation: Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611.
authors.forename: N A
authors.initials: NA
authors.lastname: Simerl
authors.forename: C J
authors.initials: CJ
authors.lastname: Wilcox
authors.forename: W W
authors.initials: WW
authors.lastname: Thatcher
authors.forename: F G
authors.initials: FG
authors.lastname: Martin
mesh_terms: D000367:Age Factors; D000818:Animals; D001947:Breeding; D002417:Cattle / Q000235:genetics / Q000502:physiology*; D002418:Cattle Diseases / Q000453:epidemiology* / Q000235:genetics; D004420:Dystocia / Q000453:epidemiology / Q000235:genetics / Q000662:veterinary; D004716:Endometritis / Q000453:epidemiology / Q000235:genetics / Q000662:veterinary; D005260:Female; D005306:Fertilization; D005313:Fetal Death / Q000453:epidemiology / Q000235:genetics / Q000662:veterinary; D015994:Incidence; D007744:Obstetric Labor Complications / Q000453:epidemiology / Q000662:veterinary*; D010922:Placenta Diseases / Q000453:epidemiology / Q000662:veterinary; D011247:Pregnancy; D012098:Reproduction / Q000235:genetics / Q000502:physiology*