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Submitted to: American Society of Animal Science Southern Section Meeting
Publication Type: Proceedings
Publication Acceptance Date: 11/22/2005
Publication Date: 1/3/2006
Citation: Ferrell, C.L. 2005. Maternal and fetal genotype influences on fetal growth. Symposium on Tropically Adapted Breeds, Southern Cooperative Series Bulletin 405, American Society of Animal Science Southern Section Meeting, p. 89-95.

Interpretive Summary: Data have been presented to show that fetal growth is primarily a function of fetal genotype. However, it is evident that the ability of the fetus to express its full growth potential is frequently constrained, to varying degrees by the maternal uterine environment, especially during latter stages of gestation. Maternal constraint of fetal growth appears to be, in part, mediated by perfusion and function of uteroplacental tissues. Consequences of restricted placental development early in gestation may not become evident until late in gestation, or during the postnatal period. There is some evidence that fetal tissues may be differentially affected by maternal constraint possibly because of differing priorities, or simply timing of development. In addition, the effects of maternal constraint may not be fully reflected by birth weight, or tissue weight alone, and may have consequences beyond the perinatal period.

Technical Abstract: Objectives are to review influences of maternal and fetal genotype on fetal growth and development. Brahman (Br) cows with Br or Charolais (C) fetuses and C cows with Br or C fetuses were used. Indwelling catheters were placed in a uterine artery, uterine vein, umbilical vein, fetal femoral artery, and fetal femoral vein at 220 ± 0.4 d after embryo transfer. Uterine and umbilical blood flows (L/min) and net uptakes of glucose, lactate, alpha-amino N, urea N, and ammonia N by the gravid uterus, fetus, and uteroplacenta were determined on 227 ± 0.4 d. Cows were killed on 232 ± 0.5 d or 271 ± 0.7 d. Weights of the fetus, fetal membranes, cotyledons, caruncles, and uterus were recorded as were weights of the fetal liver, heart, kidneys, spleen, lungs, stomach complex, intestines, and semitendinosus muscle. Data were analyzed by analysis of variance with breed of cow (CB), breed of fetus (FB), day of gestation (D), and all interactions were included in the model as fixed effects. Uterine blood flow in Br cows with Br (5.01 L/min) or C (4.66 L/min) fetuses was similar, but less (P < 0.01) than in C cows with Br (7.14 L/min) or C (9.24 L/min) fetuses, which differed (P < 0.01). Umbilical blood flows of C (3.78 L/min) were greater (P < 0.01) than those of Br (2.29 L/min) fetuses. Fetal uptake of oxygen, glucose, and alpha-amino N, gravid uterine uptake of alpha-amino N, and uteroplacental uptake of glucose were greater for C than for Br fetuses. Gravid uterine oxygen uptake and uteroplacental lactate release were influenced by CB x FB. Fetal weights were influenced (P < 0.01) by CB, FB, D, CB x D, and tended (P = 0.07) to be influenced by CB x FB x D. Caruncular weights were greater for C than for Br cows (P < 0.05) or fetuses (P < 0.01) and were greater (P < 0.05) at 271 than at 232 d, but FB was the only significant source of variation in cotyledon weight, RNA, DNA, or protein. Results demonstrated that maternal uterine environment influences fetal growth and suggests those influences are mediated, in part, by growth and function of placentomal tissues and uterine blood flow.