Ultrasonographic assessment of embryonic, fetal and placental development in Ossimi sheep

The aim of the present study was to determine the pattern of fetal growth in breeds characterized by low litter size and birth weight. Also, accuracy of the fetal kidney length (KIL) in predicting the gestational age (GA) in sheep was investigated. In experiment 1, serial ultrasonographic examinations were performed in 12 Ossimi ewes for a total of 336 times between days 22 and 146 of gestation. Sequential changes of the fetal crown-rump length (CRL), diameter of the amniotic vesicle (AVD), chest depth (CHD), abdominal diameter (ABD), eyeball diameter (EBD), ruminal length (RUL), placentome diameter (PLD), and kidney length (KIL) were recorded. Changes in echogenicity of the placentome and fetal fluids, and beginning of ossification were registered. Regression models for estimation of the gestational age were derived from the biometric indices. In experiment 2, the KIL was estimated in 30 Ossimi ewes and the GA was calculated with the mean squared predicted errors method. The value obtained was compared with the actual GA. The embryo and amniotic vesicle were first observed by days 25.38±1.2 and 28.67±1.0, respectively. Organization of the embryo into head, body and limb buds was detected by day 38±3.2. Ossification was observed on the head, ribs and vertebrae by days 44.86±2.5, 50.25±3.4 and 51.50±2.5, respectively. The amniotic fluid remained clear and echo-free until day 80.67±11.2, then it became slightly turbid. Definite turbidity was observed by day 103.0±8.0. Echogenic spots appeared in the allantoic fluid by day 138.0±9.5. The placentome increased in size until day 82.73±7.7, then it began to collapse. The fetal kidney was first visualized by day 73.2±6.3. Its mean long axis increased linearly from 1.41±0.2 cm on day 76 to 3.61±0.3 cm on day 146 (Y = 0.0345X−1.2052, R2 = 0.81). Except the PLD, regression and correlation coefficients of the various measurements on gestational age were high significant. Using the KIL—predicting equation, no significant difference was found between the expected and observed fetal ages. In conclusion, sonographic fetometry in Ossimi sheep can be valuable for the evaluation of fetal development, the estimation of gestational age and the prediction of parturition dates. The KIL was easy to make and could therefore be included into the model for dating pregnancies. The times of organization, ossification, turbidity of the fetal fluids and degeneration of placentome might be helpful in judging the fetal age. © 2007 Elsevier B.V. All rights reserved.