Transabdominal ultrasound evaluation of bovine fetal development in late gestation
Résumé
Transabdominal ultrasound evaluation of fetal health has been initially developed in the equine species to monitor fetal health in high-risk pregnant mares. This technique was subsequently used to assess bovine fetoplacental development, particularly in the context of the diagnosis of large offspring syndrome in IVP and SCNT pregnancies. So far, studies have focused on placental pathology and hydrops as a means to establish a prognosis for on-going pregnancies and to decide whether or not to terminate the pregnancy. The use of aortic diameter as a predictive measurement for calf weight, as used in horses, was also shown to be unreliable due to the high frequency of enlarged cardiac development in IVP calves. The objective of the current study was to evaluate the use of intercoastal measurements to monitor fetal growth and predict calf weight in bovine pregnancies obtained after both IVP or AI. Nineteen heifers of 4 different breeds transferred with 1 or 2 SCNT embryos and 11 Holstein heifers bred by AI were monitored by ultrasound every fortnight from 150 days of gestation using a Voluson-i (GE Medical Systems) equipped with a multifrequency transab- dominal probe (2.2–6.5 MHz), allowing the visualization of fetuses. The width of the rib closest to the caudal side of the heart and of the intercostal width (ICW) at the cardiac level was measured. Calf weight was recorded at birth or at maternal euthanasia. Nineteen heifers delivered live calves at term (n = 8 SCNT and 11 AI), 1 NT calf was stillborn, and the others died between 150 and 280 days. Data throughout gestation were analyzed by linear regression and correlations between the last ICW measurement and calf weight were performed using the Pearson test. Differences between groups during gestation were analyzed by ANOVA. ICW increased significantly with time in both groups, with a linear increase and the same slope (r2 = 0.62 and 0.72 in SCNT and AI, respectively), although ICW were significantly larger in SCNT (P < 0.0001). There was a significant positive correlation (r2= 0.53, P < 0.0001) between last ICW and calf weight. These data indicate that ICW may be useful to predict calf weight at birth and to prepare appropriate management of calving. More data are needed to establish more stringent correlations.