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. The number of animals suffering from a range of inherited disorders was estimated based on breeding results, pedigree, and data on the genotype of sires. It was estimated that around 12,000 embryos had suffered from complex vertebral malformation. The total costs related to these cases came to £ 5 million (2005 level) if estimations of the costs associated with a single case of complex vertebral malformation from the United Kingdom were adapted. Spinal muscular atrophy was the most important disease in the Danish Red Dairy breed with around 1,800 cases. The number of animals suffering from inherited disorders during the 1970s or earlier could not be estimated due to poor data quality. The annual number of affected progeny was determined for each disease and the efficiency of the control measurements implemented by the breeding associations was evaluated. The number of diseased animals had been reduced to around zero for most disorders, but the time span needed to achieve this varied considerably. A rapid decrease in the number of affected progeny was observed if control measurements were based on molecular genotyping, while a prolonged decrease was seen if control measurements were based on progeny examination. The findings demonstrate the superiority of molecular genotyping to progeny examination in programmes to identify heterozygous sires and reduce the negative effects of inherited disorders. Estimations of the number of animals suffering from hereditary dilated cardiomyopathy showed that more than 100 cases had occurred. Hereditary dilated cardiomyopathy has only been diagnosed fortuitously and information on affected breeding lines is probably faulty. The number of cases may therefore be considerably higher and increased surveillance of this disorder is recommended. Renal lipofuscinosis is highly prevalent in Danish Holsteins and the Danish Red Dairy breed. Further research is needed to evaluate whether the increased culling rate of affected cows is a real or merely an accidental finding. A review of inherited disorders and their present significance in Danish cattle is given, focusing on the morphology and inheritance of the disorders, and providing information on affected breeding lines. Other important aspects of the disorders are described, especially the aetiology and pathogenesis. The review includes chondrodysplasia, complex vertebral malformation, osteogenesis imperfecta, syndactylism, acroteriasis, congenital paralysis, bovine progressive degenerative myeloencephalopathy, spinal muscular atrophy, spinal dysmyelination, syndrome of arthrogryposis and palatoschisis, ichthyosis foetalis, epitheliogenesis imperfecta, hereditary zinc deficiency, renal lipofuscinosis, hereditary dilated cardiomyopathy, bovine leukocyte adhesion deficiency, congenital erythropoietic porphyria, rectovaginal constriction, chromosomal aberrations, and defects of spermatozoa. © 2007 The Authors.
