ULTRASONOGRAPHIC FEATURES OF CANINE PREGNANCY WITH SPECIAL REFERENCE TO FETAL DEVELOPMENT AND HEALTH.

Nowadays ultrasonography represents the gold standard method for the evaluation of canine fetal development and health. In dogs, the gestational age is estimated by the ultrasonographic measurements of extra-fetal and fetal structures. The fetal development has been deeply investigated in small and medium dogs, whereas only few information are available for large and giant size bitches, even though they are very popular canine breeds. The measurements of the inner chorionic cavity (ICC) in early pregnancy, and the biparietal diameter (BP) in late pregnancy are commonly used in clinical practice. Both ICC and BP are highly reliable when size-related specific formulae are applied, thus, specific equations for large and giant dogs would allow the most accurate prediction of parturition term. Only few parameters are available to objectively assess the fetal health during canine pregnancy. Among them, the fetal heart rate (FHR) is generally used, but the relationship between FHR and maternal heart rate (MHR) has been poorly investigated. The availability of reference values of the ratio FHR/MHR, could better contribute to the evaluation of the fetal health at different gestational ages, than the single FHR values. The aims of this study were 1) to derive the growth curves of extra-fetal and fetal structures (ICC and BP) in large and giant size bitches and to evaluate their accuracy (Paper 1); 2) to evaluate the trend of FHR and of the ratio FHR/MHR in bitches of different pre-gestational bodyweight (Paper 2). Present results showed a significant relationship between days before parturition and ICC or BP in large and giant size bitches. The overall accuracy ±2 days of both parameters was significantly higher than the accuracy ±1 day. Only in giant bitches, the BP accuracy of the prediction was significantly lower in small than normal litter size. As previously observed in other sizes dogs, the gender did not affect the accuracy of the prediction. The second study demonstrated that both FHR and FHR/MHR significantly fitted a multiple quadratic regression for all independent variables. They both resulted higher in low and high bodyweight, and reached the maximum values at about 20 days before parturition. Maternal pre-gestational bodyweight and the gestational age influenced both FHR and FHR/MHR. The highest significance of FHR/MHR, compared to FHR, encourages the application of this ratio, to evaluate fetal health. The derived equation for FHR/MHR ratio, that describes the trend in healthy fetuses, could be helpful in clinical practice to derive expected values in uncomplicated pregnancies.