Inherited Disorders in Danish Cattle

Department of Veterinary Pathobiology Faculty of Life Sciences University of Copenhagen Bulowsvej 17 DK-1870 Frederiksberg C Denmark Inherited disorders are of great concern in cattle breeding as the breeding systems and the extensive use of genetically related sires predispose to increased frequency of recessively inherited disease genes in the population and subsequently the occurrence of diseased animals. Inherited disorders may in this way contribute significantly to the extent of calf diseases and mortality as elite sires may produce hundreds of thousands of progeny. Furthermore, high numbers of defective animals may be reached due to international trade with semen, which links national cattle populations together genetically. Several inherited disorders have been recorded in Danish cattle, mainly in Danish Holsteins and the Danish Red Dairy breed. These two breeds are the first and third most common breeds in Denmark, which may partly explain this observation. The structure of the beef cattle industry in Denmark - with few purebred animals and many small herds - makes recognition of inherited disorders in beef cattle difficult. Sires used for breeding purposes in Denmark are labelled for specific inherited disorders if they are genetically related to known carriers or if they have been genotyped. The labelling system includes disorders such as complex vertebral malformation, bovine leukocyte adhesion deficiency, spinal muscular atrophy, and spinal dysmyelination. Animals may be labelled as non-carrier, confirmed carrier, likely carrier or possible carrier based on, for example, molecular genotyping, progeny examination or pedigree information. A complete list of sires that are carriers of an inherited disorder and have been used for breeding in Denmark is provided. The genotype of sons of heterozygous sires used for insemination was evaluated to determine if all carriers had been detected. The analyses demonstrated that labelling of sires based on examination of diseased progeny reported by breeders or veterinarians was insufficient to detect carriers. A targeted search for specific inherited disorders is therefore recommended in the future, i.e. through contact with owners of animals at high risk of developing disease. Such animals can be picked out based on breeding and pedigree information, which is available from the Danish Cattle Database. Molecular genotyping is an efficient way to distinguish between carriers and non-carriers, but this method is only applicable once the molecular basis of a disorder has been established.