"Effects of Parity Order, Age at First Calving and Season of Calving on Productive Performance of Friesian Crossbred Cattle in Sudan". Journal of Veterinary Medicine and Animal Production 8, no. 2 (سبتمبر 29, 2021). تاريخ الوصول مايو 25, 2026. https://onlinejournals.uofk.edu/vet/article/view/271.