Evaluation of genetic, common-litter, and within-litter effects on preweaning mortality in a birth cohort of puppies

Objective-To determine relative impact of genetic, common-litter, and withi n-litter factors on puppy mortality. Animals-2,622 Boxer puppies of 413 litters born during a 14-month period. Procedure-For each puppy, pedigree was determined, and litter in which it w as born was registered. Overall mortality and mortality per specific cause of death were analyzed by use of a model that included an additive genetic effect, common-litter effect, within-litter effect, and regression of morta lity on inbreeding coefficient. Relative importance of the effects was dete rmined from estimates of the variance in mortality explained by each factor . Results-22% of the puppies died before reaching 7 weeks old. Stillbirth was the most frequent cause of death, followed by infection. Most observed dif ferences were attributable to within-litter factors, which explained 67% of the variance in death attributable to infection and less than or equal to 96% of the variance in death artributable to asphyxia. Common-litter factor s were more important than additive genetic factors. Variance attributed to common-litter factors ranged from 2% for cheiloschisis, palatoschisis, or cheilopalatoschisis to 30% for death attributable to infection, and varianc e attributed to additive genetic factors ranged from 0% for asphyxia to 14% for euthanatized because of white color. Inbreeding coefficient had a sign ificant effect an death attributable to infection, which increased 0.26% fo r each percentage increase of inbreeding. Conclusions and Clinical Relevance-Additive genetic factors have less impac t on preweaning mortality than common-litter factors, which in turn have le ss impact than within-litter factors. Mortality attributable to; infection increases significantly with increases in inbreeding.