UTERINE ENVIRONMENT AND BREED EFFECTS ON ERYTHROPOIESIS AND LIVER PROTEIN SECRETION IN LATE EMBRYONIC AND EARLY FETAL SWINE

In this study we investigated erythropoiesis and fetal liver protein s ecretion during late embryonic (Day 24 and Day 30) and early fetal (Da y 40) development in pigs from domestic white crossbred (WC) gilts wit h a normal (intact; INT) or crowded (unilateral hysterectomized/ovarie ctomized; UHO) uterine environment, or from prolific Chinese Meishan ( MS) gilts. Increased fetal weight, fetal liver weight, placental weigh t, total red blood cells, hematocrit, blood hemoglobin content, and ma ternal plasma erythropoietin (EPO) levels were observed as gestation a dvanced. Cultured fetal liver secretion of transferrin and a protein o f M-r 12 500 and pI 7.5 also increased as gestation advanced. Fetal pl asma EPO declined between Day 30 and Day 40. Differential counts of ci rculating erythroid precursors revealed a decline in basophilic erythr oblasts and polychromatic erythroblasts between Day 24 and Day 40, an increase in orthochromatic erythroblasts on Day 30 followed by a drop on Day 40, and an increase in the percentage of reticulocytes/erythroc ytes from < 1.0% to approximately 90% of circulating red brood cells b etween Day 24 and Day 40. Differences among the treatment groups inclu ded a lower fetal survival percentage in UHO (vs. INT or MS) on Day 40 , and higher maternal hematocrits, fetal weights, fetal hematocrits, f etal EPO levels, and liver transferrin secretion in WC vs. MS pigs. MS pigs had a lower percentage of polychromatic erythroblasts overall an d a higher percentage of orthochromatic erythroblasts on Day 24 follow ed by a higher percentage of erythrocytes on Day 40 than WC pigs, sugg esting a more mature erythron (circulating red blood cells plus erythr opoietic tissue) in the MS pigs. Covariate analysis indicated that MS had larger placentae per unit of body weight than did WC. Conclusions were that 1) Days 24-40 of gestation is a critical time for fetal eryt hropoiesis in pigs as well as survival in a crowded uterine environmen t, 2) the MS breed may differ in the development of the fetal erythrop oietic system because of altered fetal or uterine physiology, and 3) t he UHO procedure did not significantly affect erythropoiesis in the fe tuses studied but did alter fetal survival and the relationship betwee n fetal weight and both hematocrit and hemoglobin on Day 40.