Intrauterine position and adjacent fetal sex status influences fetal and placental growth but not embryonic viability under crowded uterine conditions in pigs

Authors: Freking, Bradley - Brad; Lents, Clay

Submitted to: American Society of Animal Science Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/24/2011
Publication Date: 7/10/2011
Citation: Freking, B.A., Lents, C.A. 2011. Intrauterine position and adjacent fetal sex status influences fetal and placental growth but not embryonic viability under crowded uterine conditions in pigs [abstract]. Journal of Animal Science. 89 (E-Supplement 1):88 (Abstract #M230).

Interpretive Summary:

Technical Abstract: Intrauterine position and sex of adjacent fetuses in litter bearing species have been implicated in physiological and behavioral differences in males and females. Our objective was to quantify influences of uterine position and sex status of flanking fetuses under crowded uterine conditions and test the impact on fetal and placental growth rate. Gilts were subjected to unilateral-hysterectomy-ovariectomy surgery at 160 d of age and mated at approximately 280-d of age. Gilts were assigned to be harvested at d 45, 65, 85, or 105 of gestation. A total of 297 pregnancies were evaluated in four contemporary groups. Position in the uterus relative to the cervix, fetal status (alive, dead, mummy), fetal weight, and placental weight were recorded at harvest. Data were coded to test when each fetus was adjacent to 0, 1, or 2 opposite sex fetuses. Data were analyzed by mixed-model ANOVA procedures fitting contemporary group, line, and flanking fetal sex code as fixed effects and sire as a random effect. Nonlinear functions were fitted to the fetal and placental weight data to establish unique growth curves for each flanking sex status code. When considering only observations that had an opportunity to be flanked by two adjacent fetuses, the fraction of live fetuses represented by each classification (0, 1, 2) were 26.4%, 50.1%, and 23.4%, respectively, indicating no impact on fetal survival. Fetal weight was not influenced by flanking sex status code at d 45, but was significant (P < 0.05) by d 65, and became highly significant (P < 0.001) by d 105. Least squares means at d 105 were 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 also similarly influenced by flanking sex status code, but only apparent (P < 0.01) by d 105. Fetal growth development in pigs is influenced by sex status of adjacent fetuses, and could be a potential source of variation in behavioral and reproductive differences later in life.