Kasimanickam , R.K., Rabie L. Abdel Aziz, V.R. Kasimanickam, and C. Formen. 2017. “Calving Date Prediction Based on Transrectal Ultrasonography Determination of Gestational Age in Beef Cattle”. Clinical Theriogenology 9 (4):573-82. https://clinicaltheriogenology.net/index.php/CT/article/view/10006.