Prediction of parturition term in large and giant size bitches by ultrasonographic measurement

Introduction and aim. Fetal development has been deeply investigated in small and medium size dogs with the ultrasonographic biometry; the equations derived from the growth curves of extra-fetal and fetal parameters have allowed the prediction of parturition day (1,2). For large size dogs few information are available, and for giant dogs a correction factor to adjust the difference between actual and predicted parturition date has been applied (3). Since large and giant size bitches are well represented in canine population, specific equations to determine the day of parturition in these breeds would be useful in clinical practice. Among different parameters, inner diameter of chorionic cavity (ICC) and biparietal diameter (BP) provide an highly accurate prediction in small and medium size dogs (1,2). The aim of this study was to derive the growth curve of ICC and BP and to evaluate their accuracy in large and giant size bitches. Materials and methods. Serial ultrasonographic (SonoAce 8800, Medison Co. Ltd., Seoul, Korea) measurements of fetal parameters were performed weekly from day 20 after mating until parturition, in 8 large size (26-40 kg) and 9 giant size (>40 kg) bitches. At least three measurements of ICC or BP, according to the gestation period, were recorded and the mean values were calculated. The time of actual parturition and the litter size were reported by the owners. The relationship between ICC or BP growth and days remaining to parturition was analyzed by a linear regression model. The equations were derived as y=a+bx (y=days before parturition, x=measurement of ICC or BP (mm), a=intercept coefficient and b=first order coefficient) and the regression coefficients were analyzed by the Student's T test (p<0.05). The prediction was considered accurate when the difference between actual and predicted parturition date was within ±1 day and ±2 days. To assess the accuracy of the prediction, measurements of ICC and BP were performed in 65 and 95 ultrasound examinations of large size bitches and in 29 and 40 of giant size bitches with unknown breeding dates. To evaluate the effect of litter size on the accuracy, data were grouped for small (<5 pups), normal (5-9 pups) and large (>9 pups) litters in large and giant bitches (4). Data were analyzed by Chi-Square test (p<0.05). Results. A significant relationship between days before parturition and ICC or BP were obtained in large and giant size bitches (p<0.001). The ICC equations were y=(x-105.1)/2.5 (r2=0.92) in large, and y=(x-88.1)/1.9 (r2=0.97) in giant size bitches. The BP equations were y=(x-30)/0.8 (r2=0.99) in large, and y=(x-29)/0.7 (r2=0.97) in giant size bitches. The overall accuracy ±2 days of both parameters was significantly higher than the accuracy ±1 day in large (ICC: 83% vs. 65% and BP: 89% vs. 63%; p<0.05) and giant bitches (ICC: 100% vs. 76% and BP: 80% vs. 53%; p<0.05). With regard to litter size, no differences (p>0.05) were observed in large bitches for both parameters. In giant bitches, only the accuracy of the prediction by BP was significantly lower (p<0.05) in small than normal litter size (±2 days: 60% vs. 100%; ±1 day: 27% vs. 75%, respectively). Conclusions. The ICC and BP allow an highly accurate prediction of parturition term also in bitches of large and giant breeds. In giant bitches, when small litters are present, the lower accuracy of the prediction obtained by BP might be related to the fetuses overgrowth and/or to the consequent gestation length prolongation (5). References. 1) Luvoni and Beccaglia, Reprod Domest Anim 2006;41:27-32. 2) Lopate, Theriogenology 2008;70:397-402. 3) Kutzler et al., Theriogenology 2003;60:1309-17. 4) Beccaglia and Luvoni, J Small Anim Pract 2006;47:670-3. 5) Bobic Gavrilovic et al., Theriogenology 2008;70:783-94.