Erythrocyte and Leukocyte Parameters in Fetal Lambs

Summary Erythrocyte and leukocyte values were estimated in samples of blood from 50 ovine fetuses varying in age from 30 to 140 days after conception. The total erythrocyte count increased steadily over the range. Packed cell volume and haemoglobin values showed smaller increases, resulting in a reduction in calculated mean corpuscular volume and haemoglobin; regression equations are given. Significant numbers of reticulocytes were present between 60 and 100 days. Nucleated erythrocyte precursors decreased between 50 and 70 days. The leukocyte count rose to a peak at 130 days, followed by a decline at 140 days, refecting similar changes in the lymphocyte population. The lymphocyte/neutrophil ratio, although very variable within age groups, was always greater than unity.