Breed-specific fetal biometry and factors affecting the prediction of whelping date in the German shepherd dog

To date many studies have been published about predicting parturition by ultrasonographic fetal measurements in the bitch. Given that accuracy in such prediction is a key point for clinicians and breeders, formulas to calculate the whelping date were mainly obtained from small and medium sized dogs, which means poor accuracy when applied to large or giant breeds. Based on the evidence that ethnicity significantly affects fetal biometry in humans, this study aimed at developing a breed-specific linear regression model for estimating parturition date in the German shepherd dog. For this purpose, serial ultrasonographic measurements of the inner chorionic cavity diameter (ICC) and the fetal biparietal diameter (BP) were collected in 40 pregnant German shepherd bitches. The quality of the regression models for estimating parturition date was further verified in 22 other pregnant German shepherd bitches. Accuracy related to the prediction of parturition date was higher than previously reported: 94.5% and 91.7% within ±2 days interval based on ICC and BP measurements, respectively. Additional investigation was performed on the effects of maternal weight, age and litter size in relation to fetal biometry and to accuracy of parturition estimation. Moreover, the study included a comparison between hormonal and fetal ultrasound (ICC and BP) measurements connected to the estimation of whelping date. We suggest that specific equations from a single breed are likely to offer excellent accuracy, comparable to that of periovulatory progesteronemia, in parturition prediction and to avoid morphological variables present in dogs of different breeds even with the same size/weight.