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Volume dilution of sodium thiocyanate as a measure of extracellular fluid volume was determined in 24 normal adult horses and 4 ponies. The method employed yielded highly reproducible results on multiple determinations in individual horses. A highly significant (P less than .001) correlation between thiocyanate space and body weight was demonstrated.

Clinicopathologic effects of rapid intravenous infusion of 3 L of 5% dextrose in water containing 150 g of sodium bicarbonate were evaluated in 8 clinically normal horses. A highly significant metabolic alkalosis was produced in all the horses. This response was maximal at the end of the 20-minute infusion but persisted for as long as 8 hours. Packed cell volume, total plasma proteins, plasma potassium, and plasma chloride concentration decreased significantly after infusion, while plasma sodium concentration increased significantly. The clinical and clinicopathological responses of the horses were comparable to those in man and other animal species.

Four procedures for assessment of adequacy of colostral immunoglobulin (Ig) transfer in foals were evaluated. Results of zinc sulfate turbidity test, serum electrophoresis, total serum protein refractometry, and sodium sulfite precipitation test were compared with immunoglobulin G content determined by single radial immunodiffusion. The zinc sulfate turbidity test gave acceptable results for IgG, except that hemolyzed serum samples gave higher than expected values. A correction factor for hemolyzed serum was found to be useful. Serum electrophoresis was a satisfactory method of estimating IgG content. Total serum protein values may not be a valid basis for estimating IgG content, inasmuch as postsuckling total protein values were found to decrease in some foals in which passive transfer of IgG had been adequate. Sodium sulfite precipitation reactions were too unpredictable to be of value for determination of neonatal IgG concentration.

Eight normal horses were held without access to food or water for 72 hours during a period of high environmental temperatures. During this period, the horses had an average weight loss of 51.6 kg (10.7% of body weight). Highly significant (P less than 0.001) decreases in extracellular fluid volume (18.6 L) and plasma volume (5 L) were observed during this period as compared with base-line values. Plasma protein, sodium, chloride, and osmolality progressively increased in response to the dehydration, whereas packed cell volume, plasma potassium, calcium, magnesium, and phosphate were not significantly altered. The dehydration and clinicopathologic alterations produced were similar to those observed in other species in which the principal problem was a water deficit. After the end of the experimental dehydration period, the horses replaced 62% of the weight loss during a 1-hour period with access to water only.

Blood was collected from healthy Quarter Horse and Appaloosa foals at birth and at intervals until 18 weeks of age and then was processed in an automated system for serum chemical analysis, grouping the results by age. The test values were markedly different from those normally expected in adult horses. The greatest differences were in alkaline phosphatase, lactate dehydrogenase, glucose, and total bilirubin measurements. It was concluded that serum biochemical test results be compared with age-specific normal values before diagnoses are made in cases of illness.

Total daily 24-hour urinary output was obtained from 11 healthy horses fed alfalfa hay with free access to salt during periods of high environmental temperatures. Daily urinary volume averaged 15.6 L, with mean specific gravity of 1.028, osmolality of 1,040 mOsm/kg, and urinary flow rate of 1.24 ml/kg/hr. Total 24-hour sample collections of urine were also obtained from horses held without access to feed or water for periods of 24, 48, and 72 hours during high environmental temperatures. Average urine production under these conditions was 6.3 L during the 1st day; 3.2 L, the 2nd day; and 3.0 L, the 3rd day. Although total daily urinary electrolyte excretion decreased during these periods, urinary electrolyte concentrations of the major ions often remained unchanged, or in the case of sodium, actually increased. There was a highly significant correlation between the urinary excretion of the principal cations, sodium and potassium, and the principal anion, chloride. The urinary excretion of water and electrolytes appeared to remain stable after 48 hours of feed and water deprivation.