Competition for Materno-Fetal Resource Partitioning in a Rabbit Model of Undernourished Pregnancy

Abstract

The major goal of animal production is to obtain abundant and healthy meat for consumers. Maternal food restriction (MFR) is often applied in farms to reduce production costs. However, the suitability of MFR in livestock animals is questionable, as this management may compromise maternal fitness due to a severe negative energetic balance and can induce Intrauterine Growth Restriction (IUGR) and prenatal programming in the offspring. Here, we sought to determine, using pregnant rabbits, the consequences of MFR on maternal endocrine and metabolic status and conceptus development. Pregnant dams were distributed into three groups: CONTROL (ad libitum feeding throughout the entire pregnancy; mean pregnancy length being around 31 days), UNDERFED (50% MFR during the entire pregnancy) and EARLY-UNDERFED (50% MFR only during the preimplantation period, Days 0-7). Maternal leptin concentrations and glycemic and lipid profiles were determined throughout pregnancy, whilst conceptus development was assessed ex-vivo at Day 28. Placental parameters were determined by macroscopic and histological evaluations and apoptotic assessments (TUNEL and Caspase-3). The main results of the study showed that, despite MFR altered maternal plasma lipid concentration (P<0.05), there were no effects on maternal bodyweight, plasma leptin concentration or glycemic profile. Fetal crown-rump lengths were reduced in both undernourished groups (P<0.001), but a significant reduction in fetal weight was only observed in the UNDERFED group (P<0.001). Growth in both undernourished groups was asymmetrical, with reduced liver weight (P<0.001) and significantly increased brain: fetal weight-ratio (P<0.001) and brain: liver weight-ratio (P<0.001) when compared to the CONTROL group. A significant reduction in placental weight was only observed in the UNDERFED group (P<0.001), despite both undernourished groups showing higher apoptotic rates at decidua and labyrinth zone (P<0.05) than the CONTROL group. Thus, these groups evidenced signs of placental degeneration, necrosis and stromal collapse. In summary, MFR may encourage the mother to make strategic decisions to safeguard her metabolic status and fitness at the expense of growth reduction in the litter, resulting in enhanced apoptotic and pathological processes at placental level and IUGR.

Fig 1. Macroscopic images of rabbit conceptus at D28 of pregnancy.

Fig 2. Effects of MFR on maternal food intake, bodyweight and plasma leptin, glucidic and lipid concentrations during pregnancy.

Number of pregnant dams per group employed for Fig. a) and b): CONTROL = 9, EARLY-UNDERFED = 11, UNDERFED = 12; Number of pregnant dams per group employed for Fig. c) to i): CONTROL = 5, EARLY-UNDERFED = 5, UNDERFED = 5. Statistical analyses were performed by ANOVA. Data presented as mean±SEM. Different superscripts indicate significant differences between groups (P<0.05).

Fig 3. Histological findings of the rabbit placenta at D28 of pregnancy in CONTROL, EARLY-UNDERFED and UNDERFED groups.

Figures A to C: Labyrinth (Lz) and junctional (Jz) zones of the rabbit placenta in the three experimental groups. (D & E) CONTROL AND EARLY-UNDERFED groups. Densely cellular labyrinth with endothelium lined vascular channels and trophoblasts. (F) Labyrinth of the UNDERFED group with variably spaced endothelium lined vascular channels separated by collagen fibers (stromal collapse) and trophoblasts. Figures G to I: Junctional zone in the three experimental groups. (G) CONTROL group. Dense connective tissue matrix supporting stromal cells, trophoblasts and blood capillaries that extend into the labyrinth. (H) EARLY-UNDERFED group. Dense connective tissue containing stromal cells and trophoblasts. (I) UNDERFED group. Dense connective tissue slightly thinner and supporting fewer stromal cells and trophoblasts than the two other experimental groups. The overlaying labyrinth contains moderately spaced vascular channels with decreased cellularity. Figures J to L: Decidua (D) in the three experimental groups. (J) CONTROL GROUP. Normal decidua with large vascular sinuses, stroma, fibrin and necrosis. (K) EARLY-UNDERFED group. Large vessel within the decidua surrounded by abundant edematous stroma. (L) UNDERFED group. Markedly thinned decidua layer with spaced vessels containing hyalinised walls, a thrombus, and surrounded by dense stromal collagen. Number of placentas per group: CONTROL = 8, EARLY-UNDERFED = 11, UNDERFED = 12; Statistical analyses were performed by Chi square test. In the charts and table different superscripts indicate significant differences between groups (P<0.0001), NS non-significant differences.

Fig 4. Apoptosis assessments of the rabbit placenta at D28 of pregnancy. (a) Apoptosis quantified by TUNEL (positive staining) in decidua, junctional zone and labyrinth. (b) Localization and percentage of Caspase-3 (positive immunostaining) in decidua, junctional zone and labyrinth.

Number of placentas per group: CONTROL = 8, EARLY-UNDERFED = 11, UNDERFED = 12; Statistical analyses were performed by ANOVA. Data presented as mean±SEM. Different superscripts in the charts indicate significant differences between groups (P<0.05).

Fig 5. Summary illustration showing the effects of MFR in the EARLY-UNDERFED and UNDERFED groups on placental and fetal outcome.