The effect of breed and intrauterine crowding on fetal erythropoiesis on day 35 of gestation in swine.

In a previous report, it was suggested that intrauterine crowding impaired fetal erythropoiesis and that fetal erythropoiesis was accelerated in Meishan pigs during early pregnancy. Because these conclusions were based on limited numbers of observations, the present experiment was undertaken to provide a more extensive investigation of these phenomena. Intact white crossbred gilts, unilaterally hysterectomized-ovariectomized (UHO) white crossbred gilts, and intact Meishan gilts (n = 13 to 16 per group) were mated after at least one estrous cycle of normal duration (17 to 23 d). Gilts were laparotomized at d 35 of pregnancy, the uterine horns were exteriorized and opened near each fetus, and a blood sample was collected from each fetus. The uterine horn was then surgically removed, and each fetus and placenta was weighed. All fetal blood samples were measured for hematocrit, red blood cell number, and hemoglobin. Erythropoietin and the percentages of nucleated cells and reticulocytes were also measured in blood samples from the largest and smallest living fetus in each litter. Fetal hematocrits were not affected by treatment. Blood cell counts were greater (P < 0.01) in fetuses of Meishan gilts than in White crossbred intact or UHO gilts. Hemoglobin was less (P < 0.01) in fetuses of Meishan gilts than in fetuses of White crossbred intact or UHO gilts. The percentages of nucleated (immature) cells and reticulocytes were both less (P < 0.01) in fetuses of Meishan intact gilts. Erythropoietin was also lower (P < 0.01) in fetuses of Meishan gilts. As observed previously, fetal weight was correlated (r = 0.38; P < 0.01) with blood hemoglobin concentration. These results confirm that fetal erythropoiesis in Meishan gilts is accelerated compared with White crossbred gilts. These results are consistent with the hypothesis that faster blood cell development could be beneficial to fetal survival in swine.