signs of toxicosis similar to those seen in other species included CNS depression, anorexia, oral ulcers, and soft feces. Six ponies died in 7 to 20 days; I pony was euthanatized during an acute abdominal crisis; and 3 ponies survived the study. At necropsy, the major lesions were oral and gastroin.testinal ulcerations and renal changes.

Author's address: Department of Medicine and Surgery, Veterinary Medical Teaching Hospital, Oklahoma State University, Stillwater, OK 74078.

Horse Red Blood Cells Frozen with 20% (W/V) Glycerol and Stored at -150 ° C for Five Years. Capt. C.R. Valeri, M C, USN; D.A. Valeri; A. Gray, MS; Lt Comdr T.J. Contreras, MSC, USN; Lt Comdr J.R. Lindberg, MSC, USN. A m J Vet Res 44:11, 2200-2202 (1983).

When equine RBC were frozen with 20% (W/V) glycerol and stored at -150°C for as long as 5 years, there were no adverse effects on freeze-thaw or freeze-thaw-wash reoovery or oxygen transport function. The manner in which the glycerol was added to, and removed from, the equine RBC was shown to bean important consideration in ensuring optimal freeze-thaw-wash recovery values.

Author's address: The Naval Blood Research Laboratory, Boston University School of Medicine, 615 Albany Street, Boston, MA 02118.

Reduction of the Red Blood Cell Mass of Horses: Toxic Effect of Heparin Anticoagulant Therapy. S.G. Duncan, PhD; K.M. Meyers, PhD; S.M. Reed, DVM.Am J Vet Res 44:12, 2271-2276(1983).

This study was designed to test the efficacy of heparin anticoagulant therapy in the horse and hs effect onthe formed elements of blood. Nine clinically normal, non-traumatized adult horses were subjected to 4 different heparin maintenance regimens (dosages of 320, 240, 160, and 40 U/kg of bod~¢ weight). Porcine intestinal mucosa heparin (20,000 U/ml) was injected subcutaneously every 12 hours for 96 hours (total 9 times). A loading dose of one-thir.d the maintenance dose was given IV just before the first heparin injection. Three control horses were given an equivalent volume of 0.9% saline solution.

The 2 large doses of heparin (320, 240 U/kg) resulted in an extension of the therapeutic range for heparin anticoagulant therapy ( 1.5 to 2.5x data base-line prolongation qfthe activated partial thromboplastin time (APTT)). The 160-U/kg dose maintained the APTT in the therapeutic range, and the 40- U/kg dose had no effect on the APTT.

Heparin was shown to exert a profound influence on the RBC mass of the horse. Three of the heparin regimens (320, 240, and 160 U/kg) resulted in a significant decrease in RBC numbers, PCV, and total hemoglobin content. Platele't count also was reduced in the horses when given the 320 and 240 U/kg doses. The observed increase in the mean corpuscular volume was associated with decreasing RBC numbers. Plasma proteins, serum bilirubin, free hemoglobin (plasma), haptoglobin (plasma), and urine and fecal hemoglobin values remained unchanged in all groups. Heparin anticoagulation therapy with the smallest dose (40 U/kg) had no detectable effects on the measured values, nor did the saline solution.

Author 's address: Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, College of Veterinary Medicine, Washington State University, Pullman, WA 99164.

Effects of Toxic Doses of Phenylbutazone in Ponies. Charles G. MacAllister, DVM. A m J Vet Res 44:12, 2277- 2279(1983).

Toxic doses of phenylbutazone (10 mg/kg of body weight) were administered to l0 ponies once daily for 14 days. Clinical 144

Succinylcholine Infusion Associated with Hyperthermia in Ponies Anesthetized with Halothane. S.V. Hildebrand, DVM, and G.A. Howitt, BA. A m J Vet Res 44:i2, 2280- 2284(1983).

Succinylcholine was administered by infusion to halothane- anesthetized ponies to determine dosage requirements for surgical relaxation up to 3 hours' duration. This was not possible to do, since 4 of 6 ponies studied developed severe reactions characterized by prolonged muscle fasciculations after the initial succinylchol ine dose, muscle rigidity, hyperthermia, hypercapnia, tachyardia, increasing pulse pressure, and metabolic acidosis. The reactions resembled those associated with malignant hyperthermia, a disease recognized in persons and swine.

Two ponies showed signs of the phase II or desensitization block of succinylcholine. All ponies recovered from anesthesia without signs of muscle injury.

Author's address: Department of Surgery, School of Veterinary Medicine, University of California, Davis, CA 95616.

Effectiveness of Fenbendazole against later 4th-stage Strongylus vulgarisin Ponies J.O.D. Slocombe, DVM, PhD; B.M. McCraw, PhD; P.W. Pennock, DVM,MS; J.D. Baird, BVSc, PhD. A m J Vet Res 44:12, 2285-2289(1983).

Twelve pony foals (reared worm-free) were inoculated with Strongylus vulgaris. Approximately 8 weeks later, 4 of the foals were given fenbendazole ( t 0% suspension) at a dosage rate of 10 mg/kg of body weight daily for 5 days and 4 foals were given the suspension at a dosage rate of 50 mg/kg daily for 3 days; the remaining foals were given a placebo. All treatments were administered by stomach tube. Fenbendazole was 99.6 and 97.9% effective in the 2 treatment groups, respectively, in eliminating later 4th-stage S vulgaris larvae located near the origin of major intestinal arteries. On microscopic examination of the ileocolic artery from fenbendazole-treated foals, a few larval remnants were found beneath the tunica intima in small organized mural thrombi overgrown with endothelium. It would appear that larvae are rapidly destroyed after administration of fenbendazole.

A pony foal reared on pasture and with arteriographic evidence of arteritis of the cranial mesenteric and ileocolic arteries was treated with fenbendazole (10% suspension) by. stomach tube at a dosage rate of 50 mg/kg of body weight daily for 3 days. By arteriographic examination made 4 weeks later, there was evidence of regression of the lesion, and at necropsy done a week later, there was no arteritis or larvae in the lumen of those arteries.

Author's address: Departments of Pathology and Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada N 1G2W 1.

C o n t i n u o u s Cauda l Ep idura l and S u b a r a c h n o i d Anesthesia in Mares: A Comparative Study. R.T. Skarda, Dr Med Vet, and W.W. Muir, DVM, PhD. A m J Vet Res44:12, 2290-2298(1983).

A new technique for producing continuous caudal epidural analgesia (CEA) and caudal subarachnoid analgesia (CSA) in adult horses (mares) without causing loss of pelvic limb

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