Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/2/2006
Publication Date: 9/20/2006
Citation: Vallet, J.L., Freking, B.A. 2006. Changes in fetal organ weights during gestation after selection for ovulation rate and uterine capacity in swine. Journal of Animal Science. 84(9):2338-2345. Interpretive Summary: During pregnancy, fetal organs grow at different rates relative to each other and the whole fetus during gestation. We investigated whether an increased ability of pig fetuses to withstand uterine crowding was associated with differences in the rates of growth of the fetal organs. Fetal, placental and fetal brain, liver, spleen and heart weights were measured throughout gestation in lines of pigs selected either randomly (no selection), for the number of eggs shed in each estrous cycle (ovulation rate), or for the number of piglets that will survive gestation and be born alive (termed uterine capacity, increased tolerance to uterine crowding). Results indicated that fetal weights and fetal heart weights were reduced in the line selected for ovulation rate (increased eggs results in increased uterine crowding). No differences in average organ weights were detected in pigs selected for tolerance to uterine crowding. Growth of each fetal organ relative to overall fetal and placental growth was also examined. No differences in the relative growth of the brain, spleen or heart were detected. In contrast, growth of the fetal liver relative to fetal growth differed in the line selected for resistance to crowding, suggesting that the difference in relative growth may contribute to resistance to uterine crowding. In addition, despite few associations between resistance to uterine crowding and differences in organ growth, the results also suggested the presence of mechanisms controlling growth of the fetal heart, liver and brain that might be exploited to improve the resistance of fetal piglets to crowded intrauterine conditions with further research. With further research to define factors controlling fetal organ growth, strategies might be developed to improve fetal resistance to intrauterine crowding, resulting in increased litter size and survival of neonatal piglets after birth.
Technical Abstract: We hypothesized that the ability of the fetus to alter nutrient shunting and organ growth might be associated with uterine capacity. White crossbred gilts from a randomly selected control line, a line selected for ovulation rate, and a line selected for uterine capacity (UC) were unilaterally hysterectomized-ovariectomized at 160 d of age, mated at estrus, and slaughtered at 45, 65, 85, and 105 d of gestation (9 to 18 gilts for each line-by-day combination). Analysis of the data revealed that heart weights and fetal weights were decreased in the ovulation rate line. No significant differences were obtained in fetal, placental or fetal organ weights between the control and UC lines. Allometric growth of organs was assessed by examination of slopes of the relationships between fetal organ weights and fetal weights after ln transformation. Only the relative growth of the liver differed between selection lines and was greater (P = 0.01) in the UC line compared to the control line during early pregnancy (d 45 and 65). Allometric growth of the fetal brain, liver, and heart differed with day of gestation. A "brain sparing" effect was greater (P < 0.01) on d 85 and d 105 compared to d 45 and 65. By contrast, a "heart sparing" effect was present during early gestation which disappeared in later gestation. Curiously, fetal liver weights were hypersensitive to differences in fetal weights on d 45, possibly associated with placental affects on fetal liver weight. Fetal spleen weights were proportional to fetal weights throughout gestation. These results indicate that selection for ovulation rate decreased fetal heart and fetal weights, and that selection for UC altered the relationship between fetal liver weights and fetal weights during early gestation. Results further indicate significant changes in allometric growth of organs during gestation.