Extracellular fluid distribution in tropical merino sheep

Merino ewes and wethers maturing from 12 to 53 months of age were studied for 3 1/2 years in the field at Julia Creek (lat. 21° S.) during summer and winter. Measurements were made of plasma volume and extracellular volume, plasma proteins, haemoglobin, haematocrit, and plasma electrolytes. The range of normal in apparently healthy sheep was found to be very wide. Large changes took place in the fluid volumes during the period of investigation; the changes appeared to be independent of seasons but to a great extent determined by nutrition. Poorly nourished sheep as a whole had increased extra- cellular fluid space, and the space shrank again on improved pasture. Age and sex did not influence the fluid volumes. Lactation was associated with an increase in fluid spaces, and yard feeding with a decrease. Non-tropical sheep introduced from lat. 30° S. during winter had similar fluid volumes to the tropical sheep when investigated 2 months after their arrival. Tropical Merinos at any age or season had larger plasma volumes than sheep kept in laboratory pens in Brisbane or in Melbourne