Consideration of breed specific fetal trunk diameter for the estimation of gestation age using trans-abdominal ultrasonography in sheep

Abstract The study aim was to estimate gestational age (GA), expected parturition date (EPD) and growth rate by determining fetal trunk diameter (TD). Effects of fetal-dam pelvis alignment and in utero fetal position at time of ultrasonography (UG) on fetal numbers and sex determination were also studied. Trans-abdominal UG (3–6.5 MHz) was conducted on 37 ewes with known breeding dates from Days 25–120 of pregnancy. Errors in GA and EPD were studied using an equation in the same ewes at their successive breeding when date of breeding was unknown. There were four equations, Y = 1.28861X+32.656 (R2 = 0.92), for Indigenous; Y = 1.2603X+38.075 (R2 = 0.85), for Indigenous × Garole; and Y = 0.8932X+45.916 (R² = 0.99), for Garole fetuses; and the equation, Y = 1.3565X + 32.604 (R2 = 0.94), independent of breed were computed to estimate GA and the relationship between GA and TD of different breeds. The error in estimated GA and EPD using these four equations was determined and there was comparison with the data collected using US and the previously described equations. Results indicate there was the greatest (P