Recent studies in mice indicate a requirement of erythropoietic factors for embryonic/fetal survival. Genetic “knockouts” of erythroid transcription factors, erythropoietin (EPO) or EPO receptor block erythroid development and result in severe anemia and embryonic lethality between Day 9.5 and Day 15.5 of gestation. Iron, folate, and vitamin B12 are also required for erythropoiesis and must come from a maternal source. Because initiation of fetal liver erythropoiesis is occurring during this critical time for fetal survival in swine, failure of erythropoiesis may be involved in fetal mortality and reduction of litter size. However, embryonic/fetal erythropoiesis has not been compared in normal and crowded intrauterine environments or in European and prolific Chinese Meishan (MS) breeds.
The MS breed averages 30-40% (4.0) more pigs per litter than do their domestic/occidental counterparts, presumably because of increased fetal survivability and ovulation rate, and have been used extensively in research for their enhanced reproductive characteristics. Increased litter size in MS pigs suggests that the physiology of pregnancy has been altered to alleviate some fetal loss due to intrauterine crowding. Thus, this breed provides a useful experimental model for comparison with occidental breeds when studying suspected mechanisms of fetal loss caused by decreased uterine capacity. The unilateral hysterectomized/ovariectomized (UHO) pig also provides a model of intrauterine crowding that can be used for similar purposes. The objectives of the current study were to characterize late embryonic and early fetal erythropoiesis in the pig and investigate the effects of uterine environment and breed. flovent inhaler