Effects of dam size and nutrition during pregnancy on fetal ovarian development of their offspring in sheep

This study examined the effects of maternal size at conception and nutrition during pregnancy on ovarian development in their offspring. Romney ewes were selected at mating for heavy (H) or light (L) live weights and body condition, and then allocated to either ad libitum (A) or pregnancy maintenance (M) nutrition from Days 21-140 of pregnancy, resulting in four treatment groups; HA, HM, LA and LM. Ewes were euthanised on Days 65 (P65), 100 (P100) and 140 (P140) of pregnancy to collect fetal ovarian tissue, which was processed for morphological evaluation and immunohistochemical study of AMH and GDF9 (P140 only). Fetuses from H-dams had more oocytes in the first meiotic prophase on P65 (P=0.05) than those from L-dams. On P100, LA-fetuses had more primordial and fewer primary follicles than did LM-fetuses (P<0.05). On P140, fetuses from M dams had more primordial and fewer primary follicles compared with fetuses from A dams. Also on P140, H-M fetuses had greater (P=0.05) AMH expression than L-M fetuses. These results indicate that maternal size at conception and nutrition during pregnancy exert minor effects on fetal ovarian cell number.