Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2005
Publication Date: 6/20/2005
Citation: Vallet, J.L., Freking, B.A. 2005. Effect of selection for ovulation rate and uterine capacity on fetal brain, heart, liver and spleen weights throughout gestation [abstract]. Seventh International Conference on Pig Reproduction (June 12-15, 2005; Congress Center 'Rolduc', Kerkrade, The Netherlands). p. 108. Interpretive Summary:
Technical Abstract: It has been suggested that the ability of the fetus to control organ growth may contribute to uterine capacity by improving fetal survival under crowded intrauterine conditions. To explore this possibility, we performed unilateral hysterectomy-ovariectomy (UHO) on gilts from each of the MARC control (random selection, CO), ovulation rate (selection for ovulation rate, OR) and uterine capacity (selected for uterine capacity, UC) lines at approximately 160 days of age and then mated the gilts at estrus. Gilts were slaughtered on days 45, 65, 85 and 105 of gestation (9 to18 gilts for each day/line combination). At slaughter, each fetus was weighed and then dissected and brain, liver, heart and spleen weights (65 to 105 only) were recorded (77 to 150 fetuses for each day/line combination). As expected, fetal and fetal organ weights increased dramatically throughout gestation. To allow comparisons between day/line combinations, mean fetal and fetal organ weights were calculated for each day of gestation, and then individual fetal and fetal organ weights were expressed as a percent of the overall mean for each day of gestation. This facilitated direct comparison of changes in weights across gestation and between selected lines. In addition, the percentage data were used to examine relationships between fetal organ weights and fetal weights across gestation and between selected lines. For fetal and fetal organ weights, no day by line interactions were detected. Fetal weights were less (p < .05) in the OR line compared to the CO line (97 +/ 3 vs 105 +/ 3%, respectively). Liver and heart weights were also less in the OR line (95 +/ 3 and 94 +/ 3%, respectively) compared to the CO line (104 +/ 3 and 105 +/ 3%, respectively), but brain and spleen weights were not different. No differences in fetal or fetal organ weights were observed in the UC line compared to the CO line. No day by line interactions or line effects were detected on relationships between fetal weights and fetal organ weights. The slope of the relationship between brain weight and fetal weight decreased (p < 0.01) from day 45 (0.57 +/ 0.03) to day 65 (0.36 +/ 0.02) to day 85 (0.26 +/ 0.02), which did not differ from day 105 (0.25 +/ 0.02). The slope of the relationship between fetal liver weight and fetal weight was greatest (p < .01) on day 45 (1.20 +/ 0.04) compared to the other days examined (0.99 to 1.01 +/ 0.03). The slope of the relationship between fetal heart weights and fetal weights increased (p < .01) with day of gestation from day 45 (0.75 +/ 0.04) to day 105 (0.96 +/ 0.03). Although the relationship between fetal spleen weights and fetal weights did not differ with day of gestation, the overall slope was 0.89 +/ 0.03. In conclusion, selection for OR was associated with reduced fetal weights and fetal liver and heart weights proportionately, but not fetal brain and spleen weights. The decreased weights are probably due to the increased intrauterine crowding that occurs within this selected line due to increased ovulation rate. There appears to be little evidence that selection for UC alters fetal organ growth. The slopes of the relationships between fetal weight and fetal brain weight indicate that the previously described 'Brain sparing' effect increased with advancing gestation until day 85, and a 'heart sparing' effect decreased throughout gestation. Fetal livers were disproportionately large in large fetuses on day 45 of gestation, and some 'spleen sparing' occurs throughout gestation. Although selection for UC did not appear to alter organ growth, the mechanisms of these 'sparing' effects could potentially be useful in altering fetal development and survival.