Inherited Factor VII Deficiency in Beagles and Miniature Schnauzers in Victoria, Australia and the Use of REML Analysis to Determine Heritability of the Defect
Inherited factor VII (FVII) deficiency is a disorder of haemostasis characterised by infrequent bleeding episodes in affected dogs. It has been documented in North America, the United Kingdom and Japan in beagles, miniature schnauzers, Alaskan malamutes and cross-bred dogs. There has been one reported case in an Alaskan malamute in Australia.
The occurrence of inherited FVII deficiency was investigated in clinically healthy dogs in Victoria, Australia. Coagulation results of 76 miniature schnauzers, 53 beagles, 44 Labrador retrievers and 27 greyhounds were analysed, with the Labradors and greyhounds being used as control animals for comparison with the beagle and miniature schnauzer groups.
A prothrombin time (PT) and FVII assay were performed in each animal. A dog was considered to be affected by FVII deficiency if its FVII activity was below 50% of that of a control plasma pool derived from healthy dogs of mixed breed, age and gender. A PT greater than 1.25 times that of the control plasma pool was considered to be abnormal.
There were statistically significant differences in the proportions of beagles (15/53) and miniature schnauzers (13/76) with low FVII activity compared with Labrador retrievers (2/44) or greyhounds (0/27). There was no effect of age on FVII activity in any breed tested. Desexed beagles had significantly higher FVII activity than entire beagles. Twelve of the 13 miniature schnauzers and 8 of the 15 beagles with low FVII activity had abnormal prolongation of the PT.
Analyses of three-generation pedigrees of 69 of the 76 miniature schnauzers were conducted. Heritability was determined by restricted maximum likelihood (REML) analysis using an animal model. Estimated breeding values (EBV) for the defect were calculated using a Best Linear Unbiased Prediction (BLUP) method for each of the 422 miniature schnauzers represented in the pedigrees.
A high heritability of 0.66 (SE ± 0.256) was calculated for the defect in the miniature schnauzers. There were insufficient pedigree data to perform comparable heritability studies in the beagle group.
These findings confirm the presence of inherited FVII deficiency in beagles and miniature schnauzers in Australia. The EBV calculated will facilitate future implementation of a breeding program to eliminate or reduce the prevalence of the defect in the miniature schnauzer breed.