Foetal age estimation in sheep and goats

Abstract Certain gross external features were studied in 144 caprine and 109 ovine foetuses to aid in their age estimation. Body size changes were compared to ascertain phylogenic allometric relationships between the two species. Specimen collected from the Maiduguri abattoir belonged to northern Nigerian breeds. Developmental patterns of the integument, external jugular, facial and scrotal veins and male and female external genitalia followed the same time-event and sequence in both species. Onset and sequential changes of bone formation in the calvarium (skull-roof), and sequence and completion of regional hair distribution as well as the time-event of teeth eruption were similar in both species. However, the time limit for the whole calvarium to become hard and the onset of regional distribution of hairs varied. Body weight (BW) and crown-rump length measurements showed that a caprine foetus weighing 51.13 ± 20.37 g and measuring 11.27 ± 1.36 cm (mean ± SD) at 6–8 weeks, attained a weight of 1371 ± 175.1 g and length of 31.69 ± 1.36 cm by 18–20 weeks. An ovine foetus, however, was of larger body size (6–8 weeks, 66.8 ± 15.86 g and 12.64 ± 1.28 cm; 18–20 weeks, 2111 ± 612.0 g and 43.67 ± 2.87 cm). However, relative growth changes in these parameters indicated that both species maintained similar and proportionate linear growth relationships from 6–8 to 18–20 weeks of gestation (caprine, y = 57.4 x –728.1, r = 0.924; ovine, y = 64.8 x –941.8, r = 0.965; P > 0.05, where x is crown-rump length and y is body weight). The study provided a comprehensive chronological guide to estimate ages of ovine and caprine foetuses from 6 weeks of gestation. It was concluded that, to estimate foetal age, external features which form essential components of the body are more reliable criteria than those which are guided largely by environmental and nutritional factors. Also, in general, sheep and goats seem to maintain a very close phylogenic relationship in both developmental characteristics and body shape and form.