Plasma, Blood and Extracellular Fluid Volumes in Grazing Hereford Cattle

Abstract

SUMMARY Plasma, blood and extracellular fluid volumes of 6 grazing Hereford cattle were determined at 4-monthly intervals from 2 months to 3 years of age using Evans blue and thiocyanate dilution methods. The mean plasma, blood and extracellular fluid volumes ranged from 54 ± 5·2 ml./kg., 82·2 ± 5·9 ml./kg. and 37·1 ± 2·3 l./100 kg., respectively, at 2 months of age, to 37·1 ± 3·9 ml./kg., 61·3 ± 6·4 ml./kg. and 26·3 ± 2·3 l./100 kg., respectively, at 3 years of age. Though the blood volume and plasma volume showed a slight rise towards the end of the 3-year period, there was a significant decline with age for all 3 determinations on a body-weight basis. Total fluid volumes increased with age, but total red cell volume was relatively constant for the first 2 years. Additional increases in the total fluid volumes occurred during the summer period. Variations in packed cell volume appeared to be correlated inversely with plasma volume, except in the third year, when there was a major increase in total red cell volume. The disappearance of Evans blue from the plasma was found to decrease until about 2 years of age. The disappearance was such that considerable error would result from estimating plasma volume from a single sampling, particularly in the young animal.