Prediction of ovine foetal age using real time ultrasound imaging.

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 18 PREDICTION OF OVINE FOETAL AGE USING REAL-TIME ULTRASOUND IMAGING L. SERGEEV*, D.O. KLEEMANN**, S.K. WALKER**, D.H. SMITH*, T.I. GROSSER*', T. MANN* and R.F. SEAMARK*** Determination of litter size in sheep through real-time ultrasound imaging (RUI) has the potential to have a major influence on the management of sheep through improvement s in nutritional and husbandry practices. Further refinement of husbandry practices would be possible if lambing date could be predicted using RUI. We determined the relationship between foetal age and linear measurements (head width, thoracic depth) observed via RUI (Toshiba Sonolayer-L SAL 32A with 5.08 MHZ transducer) in -12 single-, 12 twin- and 4 triplet-bearing Merino ewes. Head width or biparietal diameter was measured from a symmetrical image of the skull. Thoracic depth was estimated from. a cross-section positioned immediately posterior to the heart. Measurements were taken at weekly intervals from days 49 to 91, and then at fortnightly intervals to day 119 of gestation. Relationships between foetal age and measurements of head width and thoracic depth were determined within litter sizes using regression analysis; linear and quadratic terms were included in all models. Table 1 Relationships of foetal head width (HW) and thoracic depth (THD) with age of gestation (A) The slope and elevation of the regression lines for litter sizes 1 and 2 did not differ (P>O.OS) for head width, but the slopes of both lines varied significantly (P~0.05) when compared with the slope of litter size 3. Similarly, the slope of the line for litter size 1 for thoracic depth differed from that of litter size 3 (P<O.OS). The correlation co-efficient8 between head width and age and thoracic depth and age, were high for all litter size categories examined (Table 1). We conclude that head width and thoracic depth are suitable linear measures for predicting foetal age in the ovine species. * Roseworthy Agricultural College, Roseworthy S.A. 5371. ** Turretfield Research Centre, Rosedale S.A. 5350. *** Department of Obstetrics and Gynaecology, University of Adelaide, S.A. 5000. 547