Abstract
Brachycephalic dog breeds are regularly asserted as being less healthy than non-brachycephalic breeds. Using primary-care veterinary clinical data, this study aimed to identify predispositions and protections in brachycephalic dogs and explore differing inferences between univariable and multivariable results. All disorders during 2016 were extracted from a random sample of 22,333 dogs within the VetCompass Programme from a sampling frame of 955,554 dogs under UK veterinary care in 2016. Univariable and multivariable binary logistic regression modelling explored brachycephaly as a risk factor for each of a series of common disorders. Brachycephalic dogs were younger, lighter and less likely to be neutered than mesocephalic, dolichocephalic and crossbred dogs. Brachycephalic differed to non-brachycephalic types in their odds for 10/30 (33.33%) common disorders. Of these, brachycephalic types were predisposed for eight disorders and were protected for two disorders. Univariable and multivariable analyses generated differing inference for 11/30 (30.67%) disorders. This study provides strong evidence that brachycephalic breeds are generally less healthy than their non-brachycephalic counterparts. Results from studies that report only univariable methods should be treated with extreme caution due to potential confounding effects that have not been accounted for during univariable study design or analysis.
Highlights
Abbreviations confidence intervals (CI) Confidence interval DCRR Disorder count risk ratio EPR Electronic patient record IQR Interquartile range KC The Kennel Club OR Odds ratio
A growing body of evidence is accumulating to suggest that brachycephalic breeds are strongly predisposed to a range of disorders intrinsically related to their typical conformations, including respiratory disease[9,10], eye disease11,12, dystocia[13,14], spinal d isease[15], heat stroke and pneumonia[16]
Rapid popularity increases over the past decade for some brachycephalic breeds such as French Bulldog and Pug have led to disproportionate numbers of younger animals representing these breeds[18,19]
Summary
Abbreviations CI Confidence interval DCRR Disorder count risk ratio EPR Electronic patient record IQR Interquartile range KC The Kennel Club OR Odds ratio. An alternative approach that encompasses a wider spectrum of disorders has been to report prevalence within key individual brachycephalic breeds such as French Bulldogs, Bulldogs and Pugs but without directly including a comparator group of dogs for reference[18,19,20]. While both approaches are useful, inference from these approaches is limited to the specific disorder or breed under study, and it is challenging to Scientific Reports | (2020) 10:17251. Univariable analyses of brachycephalic health parameters are likely to be highly confounded by age and it seems sensible to account for potential confounders in analyses of breed health as a general r ule[21]
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