INTERRELATIONSHIPS AMONG CONCEPTUS SIZE, UTERINE PROTEIN SECRETION, FETAL ERYTHROPOIESIS AND UTERINE CAPACITY

Authors: Vallet, Jeff; KLEMCKE, HAROLD - FORMER ARS EMPLOYEE; Christenson, Ronald

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2001
Publication Date: 3/1/2002
Citation: Vallet, J.L., Klemcke, H.G., Christenson, R.K. 2002. Interrelationships among conceptus size, uterine protein secretion, fetal erythropoiesis, and uterine capacity. Journal of Animal Science. 80(3):729-737.

Interpretive Summary: Placental size and efficiency, uterine length, conceptus size and fetal red blood cell development during pregnancy have all be proposed to be associated with uterine capacity. Placental and fetal size have been suggested to be controlled by the early development of the embryo, which has been proposed to be controlled by uterine protein secretion, which in turn, is suggested to be influenced by progesterone secretion by the ovary during very early pregnancy. To test these concepts, interrelationships between fetal size, placental weight, early embryo development, uterine protein secretion, early progesterone secretion, fetal red blood cell development and uterine capacity were measured in two groups of gilts that were altered to remove one ovary and one uterine horn, a surgical method that makes litter size in the gilts a measure of uterine capacity. Plasma progesterone concentrations were correlated with early embryo development and uterine protein secretion. Early embryo development was not correlated with placental weight during subsequent pregnancy. Placental and fetal weights were negatively correlated with uterine capacity, but placental efficiency was not. Fetal weights were correlated with fetal red blood cell development, confirming the negative effect of low birth weight on fetal red blood cell development. Uterine length was not related to uterine capacity. Taken together, these data suggest that reduction in placental and fetal weights may lead to improved uterine capacity. This will be likely to negatively impact fetal red blood cell development and methods are needed to improve this aspect of fetal development.

Technical Abstract: The interrelationships among d 11 conceptus size, d 105 placental weight, placental efficiency, fetal erythropoiesis and uterine capacity were investigated. In experiment 1, unilaterally hysterectomized-ovariectomized (UHO) gilts were mated after at least one normal estrous cycle and slaughtered at 105 d of gestation and number of fetuses and CL, placental weights, fetal weights, hematocrits, fetal plasma iron and fetal plasma folate were measured. In experiment 2, UHO gilts were mated and plasma progesterone was measured on d 2 and 3 of gestation. On d 11, the length of the remaining uterine horn, number of CL, conceptus number, conceptus diameters, and total uterine flush retinol binding protein (tRBP), acid phosphatase (tAP), and folate binding protein (tFBP) were measured. Gilts were then mated again and slaughtered at 105 d of pregnancy and the same traits measured in group 1 were recorded. Plasma progesterone concentrations on d 2 and 3 were correlated with d 11 conceptus diameter ( = .60, P < 0.01, for each day). The tRBP (r = 0.47, P < 0.01), tAP (r = 0.51, P < 0.01), and tFBP (r = 0.49, P < 0.01) on d 11 were only correlated with d 3 progesterone concentrations. No correlations between d 11 conceptus diameters or d 11 uterine length with d 105 uterine capacity were observed. Uterine capacity was negatively correlated with placental weight, placental efficiency (measured as residual fetal weight after fitting placental weight as a covariate) and fetal hematocrit (r = -0.37, P < 0.01; r = -0.23, P < 0.05; r = -0.35, P < 0.01; respectively). Hematocrits were correlated with fetal plasma iron (r = 0.45, P < 0.01) and folates (r = 0.52, P < 0.01). Thus, reducing placental and fetal weights will likely increase uterine capacity.