Description and measurement of rates of early mortality in the pig
This bulletin demonstrates the use of life tables in studying the early mortality experienced in pigs. The plot of the surviving fraction is useful in describing the general course of mortality in the postnatal period. Comparison of survival curves are accomplished most effectively by studies of age-specific mortality rates.
The logarithm of the mortality rates in pigs declines linearly with the logarithm of time before maturity in a manner analogous to the linear increase in mortality rate found in man after age 30. This relationship allows quantitative comparisons between different groups on the basis of the slope and intercept of the line fitted to the age-specific mortality rates.
The quantitative measurement of mortality is hindered by many unique characteristics of the length of life in the early postnatal period. The transformation of length of life to a quantitative variable based on the normal distribution allows the variation in mortality to be analyzed between and within small groups, such as litters and paternal half-sib classes.