Trends In Birth Weight Research Articles

Secular Trends in Late Foetal Deaths, Neonatal Mortality, and Birth Weight in England and Wales, 1956-65

Secular Trends in Late Foetal Deaths, Neonatal Mortality, and Birth Weight in England and Wales, 1956-65

Birth weight, maternal age, and parity among the african population of uganda.

Data on birth weight maternal age and parity was obtained for 1528 maternities at Mulago Hospital Kampala between December 1956 and Septe mber 1957. The babies had a mean birth weight of 6.57 pounds + or - .03 for total births and a mean birth weight of 6.59 + or - .03 pounds for live births. Stillborn babies were significantly lighter at birth (6.24 + or - .164 pounds). Mean age and parity were similar among mothers having live babies and those with stillbirths. Male stillbirths significantly outnumbered female (66 males 38 females; .025 less than p less than .01). Both the stillbirth rate and the twinning rate was much the same among the ethnic groups represented and both were higher than in Europe. There is a definite trend for mean birth weight to increase with parity for a given maternal age; at constant parity however maternal age has no clear effect on birth weight except that very young mothers have lighter babies. Non-Bantu babies were lighter than Bantu babies although their mothers had equal or superior nutritional status. This may be related to the fact that African children have less weight per unit stature than European children which seems to be a genetic trait perhaps a climatic adaptation. There is need for detailed studies on the growth of African children. It may be that the mothers with the lightest babies will have children with the smallest per unit weight.

Selection Intensities and Time Trends for Performance Traits in Range Hereford Cattle under Mass and Recurrent Selection

Data on selection intensities and time trends in three inbred Hereford lines and their linecrosses resulting from matings to a common tester line produced at the North Montana Branch Experiment Station, Havre, Montana, were evaluated and discussed. Within-line selection was fairly intense in the three inbred lines and test line for weaning weight, postweaning daily gain, and final weight off feed. Selection pressure was much greater on the male side with the bulls used averaging about one standard deviation above the mean of the unselected population. Direct selection pressure for combining ability in the recurrent selection phase was negligible. Phenotypic time trends computed by regression of the traits on years indicated a negative trend in birth weight, weaning weight, and postweaning daily gain in the heifers, and a positive trend in postweaning daily gain of bulls and steers. Environmental trends for birth and weaning weights obtained from repeat mating information indicated a negative time trend. Estimates of genetic progress were positive for birth and weaning weights and were somewhat larger than expected. In general, those lines in which selection was most intense showed the greatest estimated genetic progress.

GENETIC TRENDS IN PERFORMANCE OF THE ROMNELET SHEEP DURING THE PERIOD OF BREED DEVELOPMENT

Performance records on the Romnelet sheep, developed from the Romney X Rambouillet cross [with introductions of Targhee and Romeldale in the early years], were analysed to determine genetic trends in birth weight, weaning weight, 18-month weight of ewes and yearling clean fleece weight from the F1 to the F7 generation.There were statistically significant (P < 0.01) reductions of 1.3 pounds in birth weight, 7.5 pounds in weaning weight at an average age of 136 days, 7.0 pounds in 18-month weight of ewes and 0.6 pound in yearling clean fleece weight from the first-cross to the F2 generation. There was a further significant (P < 0.05) decline of 0.6 pound in birth weight and a significant (P < 0.01) decline of 0.5 pound in clean fleece weight after the F2 generation, but no further significant change occurred in 18-month weight of ewes. There was a significant (P < 0.05) increase of 7.8 pounds in weaning weight in the later generations.

A contribution to the study of birth weight and survival of twins based on an Indian sample.

SummaryAn Indian sample of 277 twins has been analysed with a view to assessing the influences of certain factors on birth weight and survival. The twin birth rate shows an increasing trend with parity as well as with maternal age, the overall rate being 1 in 59. Males have higher mean birth weight than females. The means of birth weight, parity and maternal age are higher for unlike‐sex twins than those for the other group. The trend of birth weight over parity for given maternal age seems to be curvilinear. No consistent trend of the same with maternal age, parity fixed, emerges. Birth weight of one twin seems to have linear regression on that of the other. Mortality is highest for the first‐born. The trend of the rate of mortality over maternal age is highest at the lower and upper groups with a minimum in the age group 28–32. Neither sex nor group is found to have a significant differential effect on survival.