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At least 703 records · Page 39Linked to original sources
PubMed2001

Season of birth and reproductive performance: an analysis of family reconstitutions of 800 women born in The Netherlands at the end of the 19th century.

BACKGROUND: Several studies have reported associations between season of birth and reproductive characteristics such as menarcheal age, fecundability, and twinning, but the results are inconsistent with respect to the location of high- and low-risk seasons. To assess whether this disagreement could be due to the use of populations from different geographic areas and time frames instead of different etiologic pathways, we investigated the season-of-birth dependency of a variety of reproductive outcomes within one time- and area-limited population. METHODS: In a historic follow-up study, the reconstituted families of 800 women born between 1873 and 1887 in or near Rotterdam, The Netherlands, were used to determine eight types of reproductive outcome: childlessness, interval to first pregnancy, pregnancy interval, stillbirth, neonatal death, postneonatal death, multiple birth, and gender of offspring. The relation of these outcomes with season of birth was modeled using cosinor functions with periods of 1 year or a half year. Data were analyzed by use of logistic regression or general estimation equations (GEE), dependent on whether outcomes could occur more than once per woman. RESULTS: Peaks in the model-based risks of reproductive failure were found within two small temporal ranges, January 1 to February 11 and July 1 to August 11 for all outcomes except gender. The picture did not change after controlling for known and possible risk factors, including age, offspring's birth cohort, and some social variables. CONCLUSIONS: This study reconfirms the idea that seasonal factors around conception or birth influence later reproductive characteristics. Observing the consistency of the location of high-risk seasons across a variety of outcomes, the explanation of season-of-birth dependency of different reproductive outcomes need not involve multiple etiological pathways.

Female↗
PubMed1981

Bovine leukemia virus infection in a large Holstein herd: prospective comparison of production and reproductive performance in antibody-negative and antibody-positive cows.

Serum samples from lactating cows in a purebred Holstein herd were tested annually (from 1977 to 1980) for antibodies to bovine leukemia virus (BLV), using the agargel immunodiffusion test. Production and reproductive variables were obtained from Dairy Herd Improvement Association records. All milk and fat production values were converted to 3.5% fat-corrected milk (FCM). Variables examined included: FCM, 305-day actual; FCM, 305-day mature-equivalent; FCM, total lactation; FCM per day, 305-day actual; total days milked during lactation; days nonlactating; age at calving; calving interval; days open, and number of times bred. Lactations were stratified from 1 to greater than 5 for comparison of variables. A matched case-control analysis was performed to assess the risk of clinical mastitis in BLV-infected cows. The retention of BLV antibody-negative and antibody-positive cows in the herd was compared. There were no significant trends in the means of production and reproductive variables between BLV antibody-negative and antibody-positive cows. The relative risk of clinical mastitis in BLV antibody-positive cows was 1.3, which was not significant (P greater than 0.05). Survivorship analysis over 3 years demonstrated no significant difference in the retention of BLV antibody-negative and antibody-positive cows in the herd. The BLV-infected cows did not have lower milk production, poorer reproductive efficiency, increased prevalence of mastitis, or lesser longevity in the herd than did noninfected cows.

Animals↗
PubMed1999

Factors affecting reproductive performance in captive Mallard ducks.

Propagation of wild-strain Mallards (Anas platyrhynchos) in captivity is hindered by low egg fertility. Therefore, we studied the effects of captivity, age, mate choice and isolation on reproductive parameters of Mallards. Captive drakes had smaller immature testes than free-flying Mallard drakes. Captive yearling ducks weighed less than adult ducks at the beginning of the breeding season, but no differences were found between their initial clutch size, egg volume or number of clutches laid. Yearling pairs had lower egg fertility (7%) than adult pairs (80%). Egg fertility was higher (51 vs 21%) in self-chosen pairs than in randomly assigned pairs. Isolation of ducks, however did not influence egg production.

Aging↗
PubMed1983

Reproductive performance of Gyr cows: the effect of weaning age of calves and postpartum energy intake.

Two nutritional levels following parturition and five weaning ages for the calf were evaluated to study their effect of reproduction in Gyr cows in the savannas of West Central Brazil (Campos Cerrados). Early weaning of calves reduced postpartum weight losses and shortened the postpartum interval to conception. Energy level did not affect cow weight at weaning or conception, the number of days from parturition to first estrus or the number of matings/conception; however, the postpartum period to conception was reduced (116 vs 160 d; P less than .05) for cows on the higher energy diet. Weaning age significantly affected postpartum weight loss in cows. Six months after calving, cows that nursed calves for 1 mo were 89 kg heavier than those that nursed calves for 6 mo (384 vs 295 kg; P less than .05). Cows that were nursed for 1 mo returned to estrus at an average of 40 d postpartum, which was 23 d earlier (P less than .05) than the average of the other groups nursed for longer periods of time. There was no significant difference in the postpartum period to conception among cows that had their calves weaned at 1 mo, 3 mo and cows which were nursed twice daily beginning 30 d after parturition (57, 94 and 97 d, respectively), but was less (P less than .05) for cows nursed for 5 or 6 mo (212 and 231 d, respectively). The results show that Gyr cattle are genetically capable of responding reproductively to improve nutrition and reduced lactation stress achieved through early weaning or controlled nursing.

Animals↗