77
Influence of early gestational nutrient restriction on vascularity of beef cow placentomes
Previously we demonstrated that cows nutrient restricted from d 30 to 85 had greater placentome mass and a tendency for larger fetuses in comparison with adequately fed cows, however, umbilical blood flows were similar between treatments. We hypothesized that nutrient restriction would enhance placentome vascularity in cows compared to control. To examine the effects of maternal nutrient restriction on cotyledonary (COT) and caruncular (CAR) capillary vascularity during early gestation, multiparous beef cows were randomly assigned to either 100% (CON; n = 6) or 60% NRC requirements (RES; n = 6) from d 30 to 85 of gestation. At d 85, placentomes were fixed in formalin, embedded with paraffin, cut at 5 µm, and stained for platelet endothelial cell adhesion molecule-1, rhodamine labeled lectin, and DAPI. Photomicrographs were taken with a Zeiss Imager M2 epifluorescent upright microscope with Axiovision 4.8 software. Vascularity measurements were taken utilizing Image Pro Plus Premier software and means were separated using GLM procedure of SAS for effect of maternal diet (RES vs. CON) as well as effect of tissue (CAR vs. COT). While maternal diet did not impact the area of COT and CAR tissues, there was more (P < 0.01) COT vs. CAR tissue per placentome section analyzed (47.26 vs. 13.72 ± 0.57 of 60.99 cm2 total). Maternal diet did not impact (P > 0.24) any measure of CAR capillary development. In COT, capillary size was greater (P = 0.04) in CON vs. RES (136.21 vs. 82.98 ± 16.21 µm). Moreover, capillary surface density, a measurement of potential nutrient exchange, tended to be greater (P = 0.08) in CON vs. RES cows (0.014 vs. 0.011 ± 0.001 µm). Capillary number and surface densities were greater (P < 0.01) in CAR vs. COT (669.45 vs. 271.24 ± 58.53 and 0.021 vs. 0.012 ± 0.002 µm, respectively) whereas capillary size was smaller in CAR vs. COT (55.58 vs. 109.60 ± 10.43 µm). We reject our hypothesis that vascularity was enhanced in the RES cows. Perhaps the overall increased placental surface area negated the stimulus to enhance angiogenesis. This may help explain why umbilical blood flow was similar between RES and CON fetuses on d 85 of gestation. Funded by USDA grant number 2009-65203-05812.
Keywords: gestation, placentome, vascularity