Some changes in the composition of blood during the first 24 hours after birth in normal and growth retarded lambs

Changes in the composition of blood which occurred during the first 24 hr after birth were examined in 18 lambs whose prenatal growth had been reduced by limiting the size of the placenta (group CE) and in 18 lambs born to untreated ewes (group R). The gestational period was about 4.5 days shorter in group CE than in group R and the birth-weights of group CE lambs were reduced by about 0.5 kg. At birth the PCV and the plasma concentrations of glucose were significantly higher and the plasma concentrations of thyroxine (T4) and fructose were significantly lower in group CE than in group R. During the first 24 hr the rates of change in the PCV and the plasma concentrations of insulin T4 and immunoglobulin G (IgG) were similar in the two groups, but there were significant between-group differences in the rates of change in the plasma concentrations of corticosteroids, glucose, lactate and fructose. The PCV and concentrations of T4, corticosteroids, lactate and fructose generally decreased and the concentrations of insulin, glucose, and IgG generally increased during the first day. Many of the between-group differences observed at birth and subsequently can be explained by the hypothesis that reducing the size of the placenta causes lambs to become hypoxaemic before birth and that after birth the attainment of normoxaemia in these lambs is delayed.