Ultrasonographic gestational dating in small ruminants with unknown mating dates: A breed-aware and phase-specific review

Mokhamad Fakhrul Ulum (Division of Reproduction and Obstetrics, School of Veterinary Medicine and Biomedical Sciences, IPB University, Bogor)
Nur Afiqah Mohamad Letfee (Aliyah Rizq Farm,Desaru Integrated Cattle Farm, Jalan Bandar Penawar - Sedili Kecil, Kota Tinggi, Johor Bandar Penawar, 81910 Kota Tinggi, Johor)
Adelaide José Pereira Cristovao (Animal Health Department, Faculty of Agriculture, Universidade Nacional Timor Lorosa'e)

ARSHI Veterinary Letters
Vol. 10 No. 2 (2026): ARSHI Veterinary Letters - May 2026

Unknown mating dates weaken nutritional planning, vaccination scheduling, pregnancy grouping, and parturition surveillance in small-ruminant herds. This mini review synthesizes traceable ultrasonographic equations from multiple sheep and goat breeds into a phase-specific clinical framework. Crown-rump length is most useful early, whereas head, thoracic, orbital, and long-bone measurements dominate mid and late gestation. In Baluchi sheep, occipito-snout diameter and thoracic diameter at the last-rib junction showed R2 values of 0.981 and 0.975. In Saanen goats, humerus length, heart area, and neck-to-snout distance reached R2 values of 0.962, 0.956, and 0.953. However, a biparietal diameter of 20 mm predicts 56.4-58.7 days in the evaluated sheep equations but 64.8 days in Pygmy goats. Therefore, a universal small-ruminant equation is clinically indefensible. Gestational age should be estimated with species- and breed-matched equations, two or three measurements, and a reported range rather than a precise single day.