Prevalence and prevention of deafness in the Dalmatian - Assessing the effect of parental hearing status and gender using ordinary logistic and generalized random litter effect models

The Dalmatian dog is susceptible to congenital deafness which is thought to be inherited. The condition cannot be treated or cured, but controlled breeding could prevent or minimize the occurrence. An understanding of the quantitative relationship between the relevant attributes (sex, colour etc.) and the probability of deafness is likely to be of assistance in implementing any breeding programme to eliminate the condition, Most reported studies on Dalmatians have ignored the hearing status of close parental relatives, and none has taken into account the likely positive correlations in dogs from same litters. A composite database, obtained hy merging deafness data on 1234 tested Dalmatians with Kennel Club pedigree data on 22 873 Dalmatians in the United Kingdom, has enabled us to include the hearing status of parental relatives and litter effects in our analysis. Contingency tables and ordinary logistic regression were used to obtain preliminary results which could be compared with the findings from other studies based on similar analyses. Further logistic modelling included an additional random effects term for the effect of litters to which the dogs belonged. The preliminary analysis showed that the prevalence of overall deafness in the tested Dalmatians was 18.4%, of which 13.1% were unilaterally deaf, and 5.3% were bilaterally deaf. There was no association between deafness and either testing location or coat colour but prevalence was strongly associated with parental hearing status. In Dalmatians from normal dams the prevalence (15.6%) was significantly lower than in those from untested dams (21.9%). If the parents were both normal or both untested, these figures were 15.3 and 23.6%, respectively, and significantly different. There was a significant gender effect, the prevalence being significantly higher in females (21.1%) than in males (15.5%), and this was seen in all subsets of data partitioned by parental hearing status, by locations, and by dominant coat colours. The use of generalized modelling, which included the random litter effects yielded point estimates of the prevalence of deafness which were smaller, but with wider confidence limits. Breeding from only tested and proven normal dams and sires is therefore recommended, and should reduce overall deafness to below 15% and bilateral deafness to below 4%.