Postpartum performance of dairy heifers freshening at young ages.

Records from Florida Agricultural Experiment Station dairy herd for 1144 heifers freshening from 1959 to 1979 were studied to evaluate effects of age and problems at parturition on subsequent yield and reproduction. Statistical analysis was by method of ordinary least squares analysis of variance; five measures of reproduction, survival to second lactation, and 15 measures of yield were studied. Mean first parturition age was 25.8 mo with 40% of individuals less than or equal to 23 mo; survival to second parturition was 67%. No effects of age at first parturition were detected on survival, postpartum reproductive performance, or milk composition other than lactose-mineral, chloride, and acidity percentages; effects on yield were similar to previous reports. Stillbirth did not affect subsequent reproductive performance but was associated with decreased milk yield: 181 kg or 5.2% of overall mean. Milk yield was depressed by 239 kg for retained fetal membrane, 173 kg for dystocia, and 98 kg for metritis; milk composition essentially was unaltered. Heritability of postpartum days to first estrus was .14; estimates were 0 for days to first service, days open, and calving interval. Additional research is needed on interrelationships of gestation length with subsequent yield and reproduction and in alleviating detrimental effects of problems at parturition.

Prepartum and peripartum reproductive performance of dairy heifers freshening at young ages.

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.

Genetic and environmental effects upon reproductive performance of Holstein crossbreds in the Sudan.

Data from a herd near Khartoum for 1955 to 1977 were evaluated. Climate was semidesert with most rainfall (151 of 165 mm) in July through September. Mean maximum daily temperatures ranged from 30.7 (January) to 41.1 degrees C (May); mean minima were 14.6 degrees C (January) and 26.9 degrees C (June). Original base population (1907) was Butana with additions of Butana, Dairy Shorthorn, Ayrshire, Guernsey, and Holstein. Breed groups and % Holstein were 1, 0 to 25%; 2, 26 to 49%; 3, 50%; 4, 51 to 71%. Numbers and mean performance were gestation length, 2474, 279 d; services per conception, 2403, 2.07; calving interval, 4004, 441 d; days open, 3204, 165 d. Calving intervals (1689) were shorter for Group 3 -25 to -31 d as were postpartum days open (-27 to -31 d), and number of services per conception was lower (.21 to .37). These animals were Holstein by Butana crossbreds, so their superior performance could reflect effects of heterosis. Gestation lengths were affected by month of parturition (January greater than June, 5.6 d), which also affected services per conception (March greater than August, .75 services). Over time, not gestation length but services per conception, calving interval, and days open increased. Repeatabilities and heritabilities for these measures were .14 and .07; .07 and 0; .10 and 0; .07 and 0. Phenotypic correlation between days open and calving interval was .99 and with gestation length was -.12. Other phenotypic correlations ranged from -.01 to -.04. Heritability of age at first parturition (888) was .31. Estimates were similar to those from temperate dairy areas.