Inherited Defect of Blood Clotting Factor VIII (Haemophilia A) in Sheep

Between 1979 and 1982, several male offspring of a single ewe in the sheep flock (White Alpine sheep) at one of the experimental stations of the Swiss Federal Institute of Technology (ETH) were born with a severe bleeding disorder (1). They all died several hours post partum due to bleeding from the umbilical cord. Daughters and grand-daughters of this ewe also gave birth to male lambs showing the same syndrome. Autopsies (Department of Pathology, Faculty of Veterinary Medicine, University of Zurich) confirmed that the afflicted males suffered from extensive subcutaneous and intramuscular haematomas, especially in the muscles of the hind legs and in musculus psoas minor or musculus iliopsoas. Occurrence of spontaneous haemarthrosis, mainly in the weight-bearing joints, was frequent (2). As a consequence, the animals showed signs of pain during standing up for nursing and walking, frequently resulting in a state of general crisis. Laboratory tests, reported in this communication, indicated a prolongation of the partial thromboplastin time by a factor of two to three, and a decrease of blood clotting factor VIII (FVIII) below the 5% level, both compared to healthy female sheep (1, 2). Similar cases of haemophilia in sheep have not been previously described. A widely based search for similar defects in flocks of private sheep breeders in Switzerland did not reveal any other afflicted animals. It seemed likely that the observed clotting disorder was analogous to human haemophilia A. Laboratory investigations. Blood was withdrawn from the jugular vein into Polyperen tubes (Milian SA, Geneve) containing 0.11 M sodium citrate, in a volume ratio 1:10. The samples were spun for 10 min at 2,000 × g (4° C). The platelet-deficient plasma was separated with a plastic pipette and stored in an ice bucket before using. A coagulometer according to Schnittger and Gross (an instrument of Heinrich Amelung GmbH, Lemgo FRG) was employed. Activated partial thromboplastin time (PTT), prothrombin time (PT, Quick-test), and thrombin time (TT) were assayed in platelet-deficient plasma after recalcification. Corresponding Boehringer Mannheim kits were employed. Average values of control animals were estimated and analyzed earlier (1). The single-step method was applied for determination of individual blood clotting factors: the test plasma was mixed with a standard volume of reagent plasma deficient in the factor to be investigated, and PTT (for factors of the intrinsic pathway) or PT (for factors of the extrinsic pathway) were estimated. Test kits of Merz -IDade AG, Düdingen, Switzerland, were employed. Since no standard sheep calibration plasma was available, the coagulation status of animals was based on comparisons with a plasma sample pooled from 15 normal female nonestral nonpregnant sheep (months January to April), measured in various dilutions. For calibration purposes, this pooled plasma was diluted with Owren's veronal buffer pH 7.35 (Merz + Dade AG), usually in ratios 1:5 to 1:200; clotting times for each diluted sample were measured. Clotting time of the test plasma was estimated at 1:10 dilution and compared with the calibration profile. Identification of carriers. The blood clotting defect was originally observed in male offspring of a single ewe (cf. Fig. 1, animal No. 157) and a ram without apparent blood clotting anomalies.