Intrauterine position and adjacent fetal sex affects fetal and placental growth throughout gestation, but not embryonic viability, in pigs selected for component traits of litter size

Authors: Lents, Clay; Freking, Bradley - Brad

Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2019
Publication Date: 10/1/2019
Citation: Lents, C.A., Freking, B.A. 2019. Intrauterine position and adjacent fetal sex affects fetal and placental growth throughout gestation, but not embryonic viability, in pigs selected for component traits of litter size. Animal Reproduction Science. 209:106139. https://doi.org/10.1016/j.anireprosci.2019.106139.
DOI: https://doi.org/10.1016/j.anireprosci.2019.106139

Interpretive Summary: Prenatal programming of mammalian fetuses has long-lasting biological and pathological effects on adults later in life. In pigs, limitations in uterine space, called uterine capacity, are thought to influence prenatal programming and an overcrowded uterine environment leads to a wide range of negative consequences for pigs after birth and throughout life. ARS scientists at Clay Center, Nebraska, used traditional genetic selection to develop a unique genetic line of pigs that have greater uterine capacity and found it reduced fetal loss. They used these selected genetic lines to understand how uterine capacity may influence prenatal development when litter sizes create crowded conditions. Scientists discovered that location within the uterus has dramatic effects on fetal development throughout gestation. Fetuses located at the ends of the uterus were significantly larger than pigs that developed in the middle of the uterus. Additionally, the sex of adjacent fetuses also had remarkable effects on fetal growth. Growth of fetuses through gestation was reduced when they were flanked by fetuses of the opposite sex. Surprisingly, increased uterine capacity did not influence the effects that intrauterine position had on fetal growth. Intrauterine position and adjacent fetal sex are important prenatal effects that program subsequent differences in pig performance after birth. This research provides critical information that will guide the implementation of advanced reproductive technologies to control sex ratios of litters thereby maximizing prenatal development and postnatal performance of pigs.

Technical Abstract: Intrauterine position and sex of adjacent fetuses in litter bearing species have been implicated in physiological and behavioral differences of offspring. The influences of uterine position and sex status of flanking fetuses under crowded uterine conditions on fetal and placental growth rate was tested. Gilts were unilaterally hysterectomized-ovariectomized at 160 d of age and mated at approximately 280 d of age, with fetal harvest at 45, 65, 85, or 105 d of gestation. Uterine position relative to the cervix, fetal status (alive, dead, sex), fetal weight, and placental weight were recorded at harvest. Each fetus was coded as adjacent to 0, 1, or 2 opposite sex fetuses and analyzed by ANOVA fitting contemporary group, line, and flanking fetal sex code as fixed effects with sire as a random effect. The fraction of live fetuses in each classification (0, 1, 2) was 26.4%, 50.1%, and 23.4%, respectively, indicating no impact on fetal survival. Fetal weight was influenced by flanking sex status between 65 d (P < 0.05) and 105 d (P < 0.001), with means at 105 d of 800.0 ± 20.3, 748.5 ± 17.8, and 672.7 ± 25.2 g, respectively for flanking sex status codes 0, 1, 2. Placental weight was similarly influenced (P < 0.01) by flanking sex code, but only at 105 d. It is concluded that fetal growth and placental development in pigs is influenced by sex status of adjacent fetuses. This could be a potential source of variation in behavioral and reproductive differences later in life.