RESUMO
Several factors influence mammalian sex ratio. In this study, the effects of parental age and litter size on the offspring sex ratio in dogs were evaluated in 602 puppies born from 101 German Shepherd litters from a breeding facility. The data was obtained from recordings of the kennel and Studbook from 1996 to 2016. A linear mixed-model analysis was performed using dam age, sire age and litter size as predictors of the percentage of males in litter. Dam age and litter size has direct effect on sex ratio. Dam age * sire age and dam age * litter size interactions are significant. When evaluating dam age by sire age, the expected male percentage in the litter is higher for old dams mated with young sires and young dams mated with old sires. Smaller percentage of males is expected for young dams mated with young sires and old dams mated with old sires. When evaluating dam age by litter size, the expected percentage of males in the litter is higher for young dams delivering big litters and old dams delivering small litters. Smaller percentage of males is expected for young dams delivering small litters and old dams delivering big litters. Dam aging increased proportion of males in litters. We concluded that offspring sex ratio is determined partially by the dam age, sire age and litter size interactions in German Shepherd dogs.