title: Haematology of foetal sheep.
abstract: OBJECTIVE
  To describe the ontogeny of blood cells throughout foetal development in sheep.
  
  
  METHODS
  A haematological study on blood and bone marrow from 42 sheep foetuses aged between 19 days gestation and full term.
  
  
  METHODS
  Virgin Merino ewes were mated and the developing foetuses removed surgically at different stages of gestation. Blood and bone marrow samples were collected, stained for cytological examination or processed for electron microscopy. Blood samples were also examined haematologically. Foetuses were incubated with 3H-thymidine and autoradiographed.
  
  
  RESULTS
  During the first 4 weeks of development primitive erythroblast constituted the majority of the circulating blood cells. Definitive erythroid cells, originating in the liver, first appeared in the blood at around 27 days gestation and entirely replaced the primitive erythroblasts by 50 days gestation. Leukocyte numbers, especially lymphocyte count, increased rapidly after 49 days gestation. Erythropoiesis predominated in the marrow of all foetuses older than 70 days. In more marrow, myelopoiesis was the major activity and lymphopoiesis was not significant.
  
  
  CONCLUSIONS
  Red blood cell numbers and haemoglobin content progressively increases during foetal development. Primitive erythroblasts are not the precursors of the definitive erythroblasts. There are no significant differences in morphological features or maturation sequence between hepatic and bone marrow erythroblasts. Myelopoiesis is a major activity of bone marrow rather than of foetal liver.
authors.affiliation: Department of Anatomical Pathology, Royal North Shore Hospital, St Leonards, New South Wales.
authors.forename: M T
authors.initials: MT
authors.lastname: Alsalami
authors.forename: L J
authors.initials: LJ
authors.lastname: Filippich
mesh_terms: D000818:Animals; D001345:Autoradiography / Q000662:veterinary; D001773:Blood Cells / Q000166:cytology; D001854:Bone Marrow Cells / Q000166:cytology; D005314:Embryonic and Fetal Development / Q000502:physiology*; D004900:Erythroblasts / Q000166:cytology; D004906:Erythrocyte Count / Q000662:veterinary; D005260:Female; D005312:Fetal Blood / Q000166:cytology*; D005319:Fetal Hemoglobin / Q000032:analysis; D005865:Gestational Age; D006410:Hematopoiesis / Q000502:physiology*; D006651:Histocytochemistry; D007958:Leukocyte Count / Q000662:veterinary; D008297:Male; D008854:Microscopy, Electron / Q000662:veterinary; D011247:Pregnancy; D012756:Sheep / Q000097:blood / Q000196:embryology*; D014599:Uterus / Q000601:surgery
chemical_list: D005319:Fetal Hemoglobin