Non-invasive study of changes in body composition in rabbits during pregnancy using X-ray computerized tomography

The objectives of this study were: 1 ) to follow changes in body composition during pregnancy using a non-invasive method; 2) to compare the results obtained with X-ray computerized tomography (CT) and with the slaughter method; and 3) to study the influence of litter size on changes in body reserves in pregnant does. Seventeen pregnant Pannon White rabbit does were examined by means of CT on the day of insemination, on days 14, 21 and 28 of pregnancy, and a few hours after parturition. At comparable time points, non-pregnant does (n = 26) were also scanned as a control group. During the CT procedure 27 images (scans) were taken from all of the animals in the body region from the scapular arch to the femoral-tibial articulation. The scans were processed by means of the computerized imaging technique, to obtain three-dimensional (3D) histograms that represented the changes in the water content, and in the fat and muscle tissues of the does. On the day after parturition all the does were slaughtered and the fat content of their empty bodies was subjected to chemical analysis. In the first 14 days of pregnancy little change was detected in body composition. Thereafter, in the abdominal region a marked increase was noted in densities corresponding to water and water-rich tissues, in correspondence with the growth of uterine contents. From day 21 of pregnancy a decrease in fat was noted in the pregnant does and an increase in the same reserves in the non-pregnant control group. To compare the fat content of animals in different physiological states so-termed fat indices were created by relating pixels corresponding to fat densities to the total number of pixels. In the same way muscle indices were created to demonstrate the changes in the muscle reserves during the experimental period. To test the accuracy of estimation by fat indices a regression analysis was carried out between the index numbers and the fat content subjected to chemical analysis. The result of this analysis showed a high correlation between the parameters examined. The same fat indices demonstrated a higher mobilisation of body reserves in does with higher litter size than in those with smaller litters.