Growth and metabolism of the ovine placenta during mid-gestation

The curse of the firstborn: Effects of dam primiparity on developmental programming in ruminant offspring

The first parity, or first pregnancy, of ruminant females has negative effects on offspring during fetal, perinatal, and pre-weaning periods which ultimately lead to diminished pre-weaning productivity. Offspring born to primiparous ruminant females can have decreased fetal and pre-weaning growth, resulting in lower body weights at birth and weaning in cattle, sheep, and goats. Moreover, mortality is greater during both neonatal and pre-weaning periods. Insults during these critical developmental windows likely also have long-term consequences on first-parity offspring through developmental programming, but less research has been done to investigate effects in the post-weaning period. Many potential physiological, metabolic, and behavioral mechanisms exist for the outcomes of dam primiparity. Although competition for nutrient partitioning between maternal and fetal growth or lactation is often cited as a major contributor, we hypothesize that the most important mechanism causing most first-parity outcomes is the relative physiological inexperience of reproductive tissues such as the uterus and mammary gland during the first pregnancy and lactation, or a "first use theory" of tissues. More research is necessary to explore these areas, as well as if primiparous dams respond differently to stressors than multiparous dams, and if stress during the first parity affects subsequent parities.

Placental insufficiency and heavier placentas in sheep after suppressing CXCL12/CXCR4 signaling during implantation†

During implantation, trophoblast cell invasion and differentiation is predominantly important to achieving proper placental formation and embryonic development. The chemokine, C-X-C motif chemokine ligand 12 (CXCL12) working through its receptor C-X-C motif chemokine receptor 4 (CXCR4) is implicated in implantation and placentation but precise roles of this axis are unclear. Suppressing CXCL12/CXCR4 signaling at the fetal-maternal interface in sheep reduces trophoblast invasion, disrupts uterine remodeling, and diminishes placental vascularization. We hypothesize these negative impacts during implantation will manifest as compromised fetal and placental growth at midgestation. To test, on day 12 postbreeding, osmotic pumps were surgically installed in 30 ewes and delivered intrauterine CXCR4 inhibitor or saline for 7 or 14 days. On day 90, fetal/maternal tissues were collected, measured, weighed, and maternal (caruncle) and fetal (cotyledon) placenta components separated and analyzed. The objectives were to determine if (i) suppressing CXCL12/CXCR4 during implantation results in reduced fetal and placental growth and development and (ii) if varying the amount of time CXCL12/CXCR4 is suppressed impacts fetal/placental development. Fetal weights were similar; however greater placental weight and placentome numbers occurred when CXCL12/CXCR4 was suppressed for 14 days. In caruncles, greater abundance of fibroblast growth factor 2, vascular endothelial growth factor A, vascular endothelial growth factor A receptor 1 (FLT-1), and placental growth factor were observed after suppressing CXCL12/CXCR4. Similar results occurred in cotyledons except less vascular endothelial growth factor in 7 day group and less fibroblast growth factor in 14 day group. Our data underscore the importance of CXCL12/CXCR4 signaling during placentation and provide strong evidence that altering CXCL12-mediated signaling induces enduring placental effects manifesting later in gestation.

Interaction between gestational plane of nutrition and lactation diet composition on lactation performance of Alpine goats of different parities

A study was conducted with 48 multiparous and 31 primiparous Alpine goats to determine the effects of different nutritional planes during gestation and lactation on feed intake, body weight, body condition score and mass index, blood constituent concentrations, and milk yield and composition. Two gestation supplement treatments (GS; Moderate versus High) were imposed for approximately 5.5 months and two lactation diets (LD; Moderate vs. High) within each GS were fed for 16 wk. The Moderate GS (14.2% crude protein; CP) was given at 1.125% body weight (BW; dry matter basis) and the High GS (16.2% CP) was consumed ad libitum, with alfalfa hay available free-choice to all animals. Moderate and High LD contained 16.0 and 16.9% CP and 34.7 and 30.4% neutral detergent fiber, respectively. Body weight (77.5 vs. 72.0 kg) and body condition score (BCS; 3.22 vs. 3.04) at 11 days before kidding were greater (P < 0.05) for High versus Moderate GS, but BW at kidding (62.6 and 64.9 kg; SEM = 1.32) and 3 days later (60.9 and 63.6 kg for Moderate and High GS, respectively; SEM = 1.32) was similar. Litter size (1.9 and 2.4; SEM = 0.59), kid birth weight (3.72 and 3.59 kg; SEM = 0.097), and litter weight (6.55 and 7.13 kg for Moderate and High GS, respectively; SEM = 0.316) were similar between GS diets. However, kid birth weight (3.44 and 3.87 kg; SEM = 0.096) and litter weight (6.23 and 7.46 kg; SEM = 0.364) were greater (P < 0.05) for multiparous versus primiparous goats. Dry matter intake during lactation was greater for Moderate than for High GS (P ≤ 0.051) in kg/day, % BW, and g/kg BW0.75. However, milk fat (3.81, 4.14, 3.85, and 3.77%; SEM = 0.132) and protein concentrations (2.49, 2.50, 2.47, and 2.49%; SEM = 0.047), and raw (2.22, 2.59, 2.39, and 2.45 kg; SEM = 0.173) and energy yields of milk (6.02, 7.42, 6.51, and 6.63 MJ/day for Moderate GS-Moderate LD, Moderate GS-High LD, High GS-Moderate LD, and High GS-High LD, respectively; SEM = 0.453) were not affected by GS, LD, or their interaction. Dry matter intake, milk and its component yields, and heat energy (MJ/day) were higher (P < 0.05) for does than for doelings, but BCS and milk protein and fat concentrations were lower (P < 0.05) for does. Blood nonesterified fatty acid concentration was not affected by any diets, but there was interaction (P < 0.05) between GS and LD for betahydroxybutyric acid concentration. In conclusion, minor to moderate magnitudes of difference in nutritional planes during gestation and lactation had little effect on reproductive and lactation performance, reflecting the considerable capacity of lactating dairy goats for compensatory changes such as feed intake and tissue mobilization and accretion.

Toward assessing the role of dietary fatty acids in lamb's neurological and cognitive development

Understanding and measuring sheep cognition and behavior can provide us with measures to safeguard the welfare of these animals in production systems. Optimal neurological and cognitive development of lambs is important to equip individuals with the ability to better cope with environmental stressors. However, this development can be affected by nutrition with a special role from long-chain fatty acid supply from the dam to the fetus or in lamb's early life. Neurological development in lambs takes place primarily during the first two trimesters of gestation. Through late fetal and early postnatal life, the lamb brain has a high level of cholesterol synthesis. This rate declines rapidly at weaning and remains low throughout adulthood. The main polyunsaturated fatty acids (PUFA) in the brain are ω-6 arachidonic acid and ω-3 docosahexaenoic acid (DHA), which are elements of plasma membranes' phospholipids in neuronal cells. DHA is essential for keeping membrane integrity and is vital for normal development of the central nervous system (CNS), and its insufficiency can damage cerebral functions and the development of cognitive capacities. In sheep, there is evidence that supplying PUFA during gestation or after birth may be beneficial to lamb productive performance and expression of species-specific behaviors. The objective of this perspective is to discuss concepts of ruminant behavior and nutrition and reflect on future research directions that could help to improve our knowledge on how dietary fatty acids (FA) relate to optimal neurological and cognitive development in sheep.

New Insight into the Role of the Leucine Aminopeptidase 3 (LAP3) in Cell Proliferation and Myogenic Differentiation in Sheep Embryonic Myoblasts

Previous genome-wide association studies (GWAS) have found that LAP3 may have the potential function to impact sheep muscle development. In order to further explore whether LAP3 expression has an important role in the development of sheep embryonic myoblasts, we conducted the spatiotemporal expression profile analysis of LAP3 at the tissue and cellular level. Then we used small interfering RNA and eukaryotic recombinant vectors to perform gain/loss-of-function analysis of LAP3. CCK-8 detection, EdU staining, and flow cytometry were used to investigate the impact of LAP3 knockdown or overexpression on the proliferation of embryonic myoblasts. In addition, cell phenotype observation, MyHC indirect immunofluorescence, and quantitative detection of the expression changes of myogenic regulatory factors (MRFs) were used to explore the effect of LAP3 on myogenic differentiation. The results showed that the LAP3 expression level in muscle tissue of fetuses was significantly higher than that in newborn lambs and adult sheep, and its expression level on day 3 of differentiation was also significantly higher than that in the proliferation phase and other differentiation time points. LAP3 silencing could significantly increase cell viability and EdU-positive cells, as well as prolonging the length of S phase of myoblasts to promote proliferation, while the results were reversed when LAP3 was overexpressed. Moreover, LAP3 silencing significantly hindered myotube formation and down-regulated the expression levels of MRFs from day 5 to day 7 of terminal differentiation, while the results were reversed when LAP3 was highly expressed. Overall, our results suggested that the expression of LAP3 impacts on the development of sheep embryonic myoblasts which provides an important theoretical basis for molecular breeding of meat production in sheep.

Mycotoxin ingestion during late gestation alters placentome structure, cotyledon transcriptome, and fetal development in pregnant sheep

Ergot alkaloids, a class of mycotoxins, induce vasoconstriction when consumed by animals and humans. Pregnant ewes (n = 16; 81.2 kg ± 7.7) were assigned fed endophyte-infected tall fescue seed (E+; 4.14 μg ergovaline + ergovalinine/g seed) or a control diet (CON; 0 μg ergovaline + ergovalinine) for increasing duration during late gestation (from gd86 to gd110 or gd133) to examine changes in placentome morphology and mRNA transcriptome, and fetal development. Exposure to E+ fescue reduced serum prolactin concentrations at gd110 and gd133 demonstrating treatment efficacy. For control ewes, cotyledon and total placentome weights decreased with advancing gestation due to remodeling of placental tissues; however, cotyledon and placentome weight did not change with advancing gestation in E+ fed ewes. Fetal brain sparing was evident in E+ exposed fetuses at gd110 and gd133 compared to CON, which demonstrates asymmetrical growth and intrauterine growth restriction. Mycotoxin exposure (E+) resulted in differential expression of 22 genes in the cotyledon tissue at gd110 but only one gene at gd133 compared to CON. These results suggest that the response to mycotoxin exposure in the pregnant sheep model has an immediate impact on placental remodeling and fetal development that persists throughout the duration of the exposure period.

Ruminant Placental Adaptation in Early Maternal Undernutrition: An Overview

Correct placental development during early gestation is considered the main determinant of fetal growth in late pregnancy. A reduction in maternal nourishment occurring across the early developmental window has been linked to a wide range of pregnancy disorders affecting placental transport capacity and consequently the fetal nutrient supply line, with long-term implications for offspring health and productivity. In livestock, ruminant species specifically experience maternal undernutrition in extensive systems due to seasonal changes in food availability, with significant economic losses for the farmer in some situations. In this review, we aim to discuss the effects of reduced maternal nutrition during early pregnancy on placental development with a specific focus on ruminant placenta physiology. Different types of placental adaptation strategies were examined, also considering the potential effects on the epigenetic landscape, which is known to undergo extensive reprogramming during early mammalian development. We also discussed the involvement of autophagy as a cellular degradation mechanism that may play a key role in the placental response to nutrient deficiency mediated by mammalian target of rapamycin, named the mTOR intracellular pathway.

Factors affecting placental size in beef cattle: Maternal and fetal influences

Our objectives were to determine the effects of dam body condition score (BCS), age of dam, and calf sex on placental size and the relationships between dam body weight (BW) and calf size with placental size. Expelled placentas and calf size at birth were collected from crossbred beef heifers and cows during four experiments (n = 22 to 39/experiment). Placentas deemed complete by visual inspection were dissected; dry weights were determined for cotyledonary and intercotyledonary tissues. Mixed linear models were used to individually determine main effects of peripartum BCS category [Thin (<5), Moderate (=5), or Fleshy (≥6)], age of dam category [Primiparous (2 yr), Young (3-4 yr), or Mature (≥5 yr)], and calf sex on placental measures. Correlations were determined for placental characteristics with prepartum dam BW, gestation length, and calf size. Thin BCS dams had lower (P ≤ 0.05) cotyledonary, total placental, and average cotyledon weights and greater placental efficiency (calf birth BW/placental weight) than moderate and fleshy dams. Intercotyledonary weight was lower (P < 0.01) in thin BCS dams compared with fleshy dams. Thin and moderate BCS dams had smaller (P ≤ 0.04) calf birth BW than fleshy dams. Primiparous dams had lower (P ≤ 0.05) total placental and average cotyledon weights than young and mature dams, yet calf birth BW was unaffected (P = 0.17). Male calves were heavier (P = 0.01) than females, yet there were no differences (P ≥ 0.59) in placental weights. Calf birth BW and heart girth had moderate positive correlations (P < 0.01) and shoulder to rump length and abdominal girth had weak positive correlations (P < 0.01) with all placental weights. Dam prepartum BW and calf flank girth had moderate positive correlations (P < 0.01) with total placental weights and weak positive correlations (P < 0.01) with cotyledonary and average cotyledon weights. Intercotyledonary weight had moderate positive correlations (P < 0.01) with gestation length and calf flank girth and a weak positive correlation (P < 0.01) with dam prepartum BW. Gestation length had a weak positive correlation (P = 0.02) with total placental weight. Number of cotyledons was not correlated (P ≥ 0.28) with any dam or offspring characteristics. In conclusion, these data suggest that both maternal age and BCS affected placental size. Calf size at birth and placental weight were positively correlated, but it is still unknown which controls and signals for the growth of the other.

Components of the insulin-like growth factor system in in vivo - and in vitro-derived fetuses of cattle, and the association with growth and development

This experiment was designed to study mechanisms affecting growth of in vivo-derived (IVD) and in vitro-produced (IVP) fetuses of cattle. Day-7 IVD or IVP cattle blastocysts were transferred to recipients, with pregnant females being slaughtered on Days 90 or 180 of gestation or allowed to undergo parturition. Uteri and contents were dissected and physically measured, and maternal and fetal plasma and amniotic and allantoic fluids were collected for IGF-1 and IGF-2 determinations, and IGFBP profile characterization. Transcripts for IGF-1 and IGF-2 mRNA in placental and fetal tissues, and IGF-1r and IGF-2r in placentomes were determined. There was a greater fetal weight in the IVP group, which was associated with greater IGF-1 and IGF-2 concentrations in maternal circulation, and changes in IGFBP profiles within fetal fluids. Day-90 IVP-derived fetuses were longer, had greater organ weights, larger placentomes, less placentome IGF-2r mRNA transcript, and greater maternal IGF-1 and IGF-2 concentrations than controls. On Day 180 and at parturition tissues from IVP-derived fetuses/calves were from larger uteri, with larger placentomes/fetal membranes, fetuses/calves weighed more, had greater fetal hepatic IGF-2 mRNA transcript, had less fetal plasma IGF-1 and greater allantoic IGF-2 concentrations, greater and lesser IGFBP activities in the allantoic and amniotic fluids, respectively, and greater glucose and fructose accumulation in fetal fluids. Components of the IGF system were differentially regulated not only according to the gestation period (Days 90 or 180) and fluid type (maternal or fetal plasma, amniotic or allantoic fluids), but also based on conceptus origin (IVP or IVD) in cattle.

Preconceptional diet manipulation and fetus number can influence placenta endocrine function in sheep

Changes in maternal nutrition during pregnancy can result in profound effects on placental function and fetal development. Although the preconceptional period holds the potential to reprogram embryonic and placental development, little is known regarding the effects of premating nutritional manipulation on placental function and fetal and postnatal offspring growth. To test this, Polypay-Dorset sheep (n = 99) were assigned to 1 of 3 nutritional treatments (n = 33/treatment) receiving 50% (UN: undernutrition), 100% (C: control), or 200% (ON: overnutrition) of maintenance energy requirements for 21 d before mating during April-May (increasing photoperiod). Thereafter, diets were the same across groups. We evaluated maternal reproductive variables and maternal and offspring weight and body mass index through weaning. Maternal plasma was collected through pregnancy until postnatal day 1 to assay pregnancy-associated glycoproteins (PAGs) and progesterone. Fertility rate was similar among treatments, but ON females had a higher reproductive rate (UN: 82%; C: 100%, ON: 145%). When correcting by total birth weight, twin pregnancies had lower PAGs and progesterone versus singleton pregnancies (P < 0.001). At birth, UN lambs were heavier than C lambs regardless of birth type (P < 0.01). Growth velocity, daily gain, and weaning weight were similar, but UN and ON females grew faster and were heavier at weaning versus C females. We demonstrated that a 3-wk preconceptional maternal undernutrition or overnutrition, when correcting by total birth weight, results in lower endocrine capacity in twin pregnancies. Preconceptional maternal undernutrition and overnutrition increased postnatal female lamb growth, suggestive of reprogramming of pathways regulating growth before conception. This highlights how preconceptional nutrition can result in marked sex-specific differences.

Fetal programming in sheep: effects on pre- and postnatal development in lambs

This systematic review and meta-analysis aim to summarize the effects of maternal undernutrition or overnutrition during pregnancy on fetal weight and morphometric measurements during pregnancy, at birth, and postnatal period in sheep. After completing the search, selection, and data extraction steps, the measure of effect was generated by the individual comparison of each indicator with the average of the control and treated group (undernutrition or overnutrition) using the DerSimonian and Laird method for random effects. Subgroup analyses were also performed for lambing order, litter size, sex, as well as level, timing, and duration of the intervention. Fetal weight during the first third of pregnancy was not affected by maternal undernutrition or overnutrition. On the other hand, undernutrition in the second and last third of gestation reduces the weight of the lamb both during pregnancy, at birth, and during the postnatal period, requiring at least 120 postnatal days to achieve the same weight as its contemporaries in the control treatment. However, this reduction in weight is not accompanied by reductions in morphometric measurements, demonstrating that the animals were lighter, but of equal size. In overnutrition, there is an increase in fetal weight in the second third of gestation. However, in the last third of the gestational period, there are no differences in fetal weight for the multiparous subgroup, but it was reduced in primiparous ewes. There are no effects of overnutrition on birth weight; however, this result is highly heterogeneous. Thus, maternal nutrition of ewe during pregnancy has effects on fetal and postnatal weight, but not on size. Furthermore, the effects of undernutrition are more homogeneous while overnutrition showed heterogeneous responses.

Maternal hypercortisolemia alters placental metabolism: a multiomics view

Previous studies have suggested that increases in maternal cortisol or maternal stress in late pregnancy increase the risk of stillbirth at term. In an ovine model with increased maternal cortisol over the last 0.20 of gestation, we have previously found evidence of disruption of fetal serum and cardiac metabolomics and altered expression of genes related to mitochondrial function and metabolism in biceps femoris, diaphragm, and cardiac muscle. The present studies were designed to test for effects of chronically increased maternal cortisol on gene expression and metabolomics in placentomes near term. We hypothesized that changes in placenta might underlie or contribute to the alterations in fetal serum metabolomics and thereby contribute to changes in striated muscle metabolism. Placentomes were collected from pregnancies in early labor (143 ± 1 days gestation) of control ewes (n = 7) or ewes treated with cortisol (1 mg·kg^-1·day^-1 iv; n = 5) starting at day 115 of gestation. Transcriptomics and metabolomics were performed using an ovine gene expression microarray (Agilent 019921) and HR-MAS NMR, respectively. Multiomic analysis indicates that amino acid metabolism, particularly of branched-chain amino acids and glutamate, occur in placenta; changes in amino acid metabolism, degradation, or biosynthesis in placenta were consistent with changes in valine, isoleucine, leucine, and glycine in fetal serum. The analysis also indicates changes in glycerophospholipid metabolism and suggests changes in endoplasmic reticulum stress and antioxidant status in the placenta. These findings suggest that changes in placental function occurring with excess maternal cortisol in late gestation may contribute to metabolic dysfunction at birth.

Shearing during late pregnancy increases size at birth but does not alter placental endocrine responses in sheep

Shearing during the latter half of pregnancy is a common practice to improve flock health and productivity. Previous studies have demonstrated that shearing pregnant ewes at mid or late pregnancy is associated with an increase in lamb birth weight. In the present study, we used singleton Polypay × Dorset pregnant sheep, to investigate the potential roles of placental function and changes in maternal metabolism in underlying this increased birth weight response. Two groups were randomly established and blocked at enrollment by animal BW, body condition score and subcutaneous adipose tissue depth. The groups were shorn (SH; n = 18) or not (C; n = 20) at gestational day (GD) 107 ± 1 (mean ± SEM). Weekly maternal plasma samples were collected between shearing and birth, but only six samples were assayed for progesterone, pregnancy-associated glycoproteins (PAG1), glucose and non-esterified fatty acids (NEFAs). At birth, sex, birth weight, and newborn body mass index (BMI) were recorded. Maternal BW during mid- to late-pregnancy was similar between groups. Shearing resulted in increased lamb birth weight and BMI (P < 0.05) regardless of fetal sex but did not affect the maternal concentration of PAG1 or progesterone from GDs 100 to 142. After shearing (GD100) and up to lambing, shorn females had higher circulating glucose concentrations (P < 0.05), but not NEFA, compared to the control group. Maternal circulating PAG1, progesterone, glucose or NEFA concentration across pregnancy did not differ according to lamb sex. Across pregnancy, birth weight was positively associated with PAG1 (P < 0.001), but not with progesterone concentrations. In conclusion, weight and BMI at birth were higher in both sexes upon shearing in singleton pregnancies. Despite PAG1 being associated with birth weight, late-pregnancy shearing did not alter the placental endocrine response. Whether other placental factors are altered upon shearing and may influence the increase in birth weight and BMI remain to be investigated.

Effect of early shearing during gestation on the productive and reproductive behavior of female sheep offspring in their first 18 months of age

The research has shown the interesting contributions of shearing in mid-gestation on the performance of lambs from birth to weaning. Other studies have reported that shearing at early pregnancy influences the development of the placenta and lamb live weight at birth. However, there was a lack of information on the effect of early-prepartum shearing on the behavior of the offspring from weaning onward. This study evaluated the effect of shearing ewes at 50 days of gestation on the growth, reproductive behavior and response to a gastrointestinal parasite challenge in the female offspring from weaning to 18 months old. Fifty-seven Polwarth female lambs were used, 22 being singles and 35 twins born to ewes either shorn at 50 days of pregnancy (PS, n = 23) or shorn at 62 days postpartum (U, control, n = 34) resulting in four subgroups: single lambs born to PS ewes (n = 8), born to U ewes (n = 14), twin lambs born to PS ewes (n = 15) or born to U ewes (n = 20). All progeny were managed together under improved pasture with a minimum forage allowance of 6% live weight on dry basis. Body weight, body condition score and fecal eggs count were recorded every 14 days from weaning to 18 months of age. Concentrations of progesterone were measured weekly (from 4 to 10 months of age and from 14 to 18 months of age) to establish the onset of puberty. Ovulation rate at an induced and a natural heat (545 ± 1.0 and 562 ± 1.0 day old) was recorded. Prepartum shearing did not affect the age at puberty or the ovulation rate of female offspring, but those born as singles were more precocious ( P = 0.03) and heavier ( P = 0.02) at puberty than twin born lambs. Both the average value of parasite egg count ( P = 0.0 7) and the Famacha index ( P = 0.02) for the entire study period were lower in lambs born to prepartum shorn ewes than those born to postpartum shorn ewes. In conclusion, shearing at 50 days of gestation did not affect the growth or the reproductive behavior of female offspring. However, female lambs born from ewe shorn during gestation showed a better response to the parasitic challenge, and further research is required to confirm this.

Impact of Ergot Alkaloids on Female Reproduction in Domestic Livestock Species

Fescue toxicosis is a multifaceted syndrome that elicits many negative effects on livestock consuming ergot alkaloids produced by endophyte-infected tall fescue. The economic losses associated with fescue toxicosis are primarily due to reproductive failure including altered cyclicity, suppressed hormone secretion, reduced pregnancy rates, agalactia, and reduced offspring birth weights. For decades, a multitude of research has investigated the physiological and cellular mechanisms of these reproductive failures associated with fescue toxicosis. This review will summarize the various effects of ergot alkaloids on female reproduction in grazing livestock species.

Ergot alkaloid exposure during gestation alters. I. Maternal characteristics and placental development of pregnant ewes1

Tall fescue [Lolium arundinaceum (Scheyreb.) Darbysh] is the primary cool season forage grass in the Southeastern United States. Most tall fescue contains an endophytic fungus (Epichloë coenophiala) that produces ergot alkaloids and upon ingestion induces fescue toxicosis. The objective of this study was to assess how exposure to endophyte-infected (E+; 1.77 mg hd-1 d-1 ergovaline and ergovalinine) or endophyte-free (E-; 0 mg hd-1 d-1 ergovaline and ergovalinine) tall fescue seed fed during 2 stages of gestation (MID, days 35-85/LATE, days 86-133) alters placental development. Thirty-six, fescue naïve Suffolk ewes were randomly assigned to 1 of 4 fescue treatments: E-/E-, E-/E+, E+/E-, or E+/E+. Ewes were individually fed the same amount of E+ or E- seed mixed into total mixed ration during MID and LATE gestation. Terminal surgeries were conducted on day 133 of gestation. Ewes fed E+ fescue seed had elevated (P < 0.001) ergot alkaloid excretion and reduced (P < 0.001) prolactin levels during the periods when fed E+ seed. Ewes switched on day 86 from E- to E+ seed had a 4% reduction (P = 0.005) in DMI during LATE gestation, which translated to a 2% reduction (P = 0.07) in DMI overall. Average daily gain was also reduced (P = 0.049) by 64% for E-/E+ ewes during LATE gestation and tended to be reduced (P = 0.06) by 33% overall. Ewes fed E+ seed during LATE gestation exhibited a 14% and 23% reduction in uterine (P = 0.03) and placentome (P = 0.004) weights, respectively. Caruncle weights were also reduced by 28% (P = 0.003) for E-/E+ ewes compared with E-/E- and E+/E-. Ewes fed E+ seed during both MID and LATE gestation exhibited a 32% reduction in cotyledon (P = 0.01) weights, whereas ewes fed E+ seed only during MID gestation (E+/E-) had improved (P = 0.01) cotyledon weights. The percentage of type A placentomes tended to be greater (P = 0.08) for E+/E+ ewes compared with other treatments. Other placentome types (B, C, or D) did not differ (P > 0.05). Total fetal weight per ewe was reduced (P = 0.01) for ewes fed E+ seed during LATE gestation compared with E-; however, feeding E+ seed during MID gestation did not alter (P = 0.70) total fetal weight per ewe. These results suggest that exposure to ergot alkaloids during LATE (days 86-133) gestation has the greatest impact on placental development by reducing uterine and placentome weights. This, in turn, reduced total fetal weight per ewe by 15% in ewes fed E+ seed during LATE gestation (E-/E+ and E+/E+).

Stage-specific feed intake restriction differentially regulates placental traits and proteome of goats

A total of twenty-four healthy twin-bearing Liuyang black goats were allocated to two trials. In Trial 1, twelve goats received either the control diet (CG, n 6, 100 % feed) or restricted diet (RG, n 6, 60 % feed of CG) from gestation days 26 to 65 after synchronisation. In Trial 2, the remaining goats were randomly and equally divided into two treatments: CG and RG from days 95 to 125 of gestation. Placental traits, fetal weight, serum parameters, nitric oxide (NO), angiogenesis gene expression and cotyledon proteome were measured at the end of each trial. In early pregnancy, the total and relative weights of placenta, uterine caruncle and cotyledon, as well as fetus, were increased (P<0·05) in RG. The NO content in maternal serum was also increased (P<0·05) in RG. In all, fifty differentially expressed proteins were identified in cotyledon. The up-regulated proteins are related to proliferation and fission of trophoblast cell and the placenta angiogenesis. During the late pregnancy trial, placental weight was increased (P<0·05) in RG, but weight of the fetus was decreased (P<0·05). The capillary density in the cotyledon was also decreased (P<0·01). A total of fifty-eight proteins were differentially expressed in cotyledon. The up-regulated proteins in RG are related to placenta formation, blood flow regulation and embryonic development. These results indicated that feed intake restriction during gestation influenced the placental and fetal development in a stage-dependent manner. These findings have important implications for developing novel nutrient management strategies in goat production.

Shearing ewes in the first third of gestation improves offspring performance

The effect of shearing ewes at 50 days of gestation on birth and weaning weight, vigour of the lambs in the first hour of life and the survival of single and twin lambs was investigated. Ultrasound pregnancy diagnosis was used to allocate 140 Polwarth ewes on Day 50 of gestation to one of four treatments, including two factors: shearing time (prepartum (PS) and postpartum (U)) and litter size (single (S) and twin (T)) resulting in the following treatments: single-bearing ewes shorn at 50 days of gestation (SPS, n = 39), single-bearing ewes unshorn (SU, n = 40), twin-bearing ewes shorn at 50 days of gestation (TPS, n = 28) and twin-bearing ewes unshorn (TU, n = 33). All ewes grazed together on improved pastures. Body condition score of the ewes was recorded once every 2 weeks from shearing until weaning, and plasma concentration of NEFA in ewes was measured once every 2 weeks from Day 30 postpartum until weaning (Day 104 ± 7). Gestation length, lamb behaviour during the first hour of life, lamb weight at birth and daily weight gain from birth to weaning and lamb survival were measured. Ewe body condition and plasma non-esterified fatty acids concentration was not affected by shearing time or litter size. Birthweight of the lambs was affected by shearing time (P = 0.0002), litter size (P < 0.0001) and sex of the lamb (P = 0.03). Lambs born to PS ewes had higher daily growth rate (P < 0.0001) than lambs born to U ewes (0.149 ± 0.07 vs 0.141 ± 0.07 kg, respectively). Birthweight affected the number of assisted lambs at birth (P = 0.01). Length of gestation was affected by shearing time (P < 0.0001). Sucking ability was improved by shearing time and litter size. Lambs born to PS ewes tried to suck (P = 0.01) and successfully sucked (P = 0.009) before lambs born to U ewes (23.3 ± 2 vs 28.7 ± 2 and 37.6 ± 1 vs 38.4 ± 1 min, respectively). Attempt and success to suck was affected by litter size (P = 0.004 and P = 0.05). TPS-born lambs tried to suck before (P = 0.004) and successfully sucked earlier (P = 0.0004) than TU lambs (26.1 ± 2.5 vs 33.7 ± 2 and 38 ± 1 vs 42.1 ± 2 min, respectively). Shearing time affected lamb survival at 20 days of age (P = 0.04). The improved survival in these lambs, expressed by a higher birthweight and vigour at birth, may be explained by better nutrition in utero in response to shearing during early pregnancy. In contrast to previous research on prepartum shearing, the present experiment shearing was done at 50 days of gestation. Early shearing in gestation might coincide with a period of high cell proliferation, intense vascular development and increased uterine and umbilical blood flows in the placenta which is in rapid development, and may result in improved outcomes when compared with shearing done on Day 70 or later of gestation.

Developmental Changes in Ovine Myocardial Glucose Transporters and Insulin Signaling Following Hyperthermia-Induced Intrauterine Fetal Growth Restriction

Developmental changes in ovine myocardial glucose transporters and insulin signaling following hyperthermia-induced intrauterine fetal growth restriction (IUGR) were the focus of our study. Our objective was to test the hypothesis that the fetal ovine myocardium adapts during an IUGR gestation by increasing glucose transporter protein expression, plasma membrane-bound glucose transporter protein concentrations, and insulin signal transduction protein concentrations. Growth measurements and whole heart tissue were obtained at 55 days gestational age (dGA), 90 dGA, and 135 dGA (term = 145 dGA) in fetuses from control (C) and hyperthermic (HT) pregnant sheep. Additionally, in 135 dGA animals, arterial blood was obtained and Doppler ultrasound was used to determine umbilical artery systolic (S) and diastolic (D) flow velocity waveform profiles to calculate pulsatility (S – D/mean) and resistance (S – D/S) indices. Myocardial Glut-1, Glut-4, insulin signal transduction proteins involved in Glut-4 translocation, and glycogen content were measured. Compared to age-matched controls, HT 90-dGA fetal body weights and HT 135-dGA fetal weights and gross heart weights were lower. Heart weights as a percent of body weights were similar between C and HT sheep at 135 dGA. HT 135-dGA animals had (i) lower fetal arterial plasma glucose and insulin concentrations, (ii) lower arterial blood oxygen content and higher plasma lactate concentrations, (iii) higher myocardial Glut-4 plasma membrane (PM) protein and insulin receptor β protein (IRβ) concentrations, (iv) higher myocardial glycogen content, and (v) higher umbilical artery Doppler pulsatility and resistance indices. The HT ovine fetal myocardium adapts to reduced circulating glucose and insulin concentrations by increasing plasma membrane Glut-4 and IRβ protein concentrations. The increased myocardial Glut-4 PM and IRβ protein concentrations likely contribute to or increase the intracellular delivery of glucose and, together with the increased lactate concentrations, enhance glycogen synthesis, which allows for maintained myocardial growth commensurate with fetal body growth.

Nutritional effects on foetal growth

The emphasis in nutritional studies on foetal growth has now moved from the last trimester of pregnancy, when most of the increase in foetal size takes place, to earlier stages of pregnancy that coincide with foetal organogenesis and tissue hyperplasia. At these stages absolute nutrient requirements for foetal growth are small but foetal metabolic activity and specific growth rate are high. It is thus a time when nutrient supply interacts with maternal factors such as size, body condition and degree of maturity to influence placental growth and set the subsequent pattern of nutrient partitioning between the gravid uterus and maternal body.

Throughout pregnancy the maternal diet controls foetal growth both directly, by supplying essential nutrients and indirectly, by altering the expression of the maternal and foetal endocrine mechanisms that regulate the uptake and utilization of these nutrients by the conceptus. Nutritional effects on the endocrine environment of the embryo during the early stages of cell division can alter the subsequent foetal growth trajectory and size at birth; so too can current in vitro systems for oocyte maturation and embryo culture up to the blastocyst stage. There is increasing evidence that subtle alterations in nutrient supply during critical periods of embryonic and foetal life can impart a legacy of growth and developmental changes that affect neonatal survival and adult performance. Identifying the specific nutrients that programme these effects and understanding their mode of action should provide new management strategies for ensuring that nutritional regimens from oocyte to newborn are such that they maximize neonatal viability and enable animals to express their true genetic potential for production.

EFFECT OF SHEARING DURING PREGNANCY ON PRODUCTIVE PERFORMANCE IN THE POST-PARTUM PERIOD OF EWES ON EXTENSIVE HUSBANDRY

The use of shearing during pregnancy has been described as a tool for improving productivity in sheep and for minimizing perinatal mortality in lambs through the increase of fetal development. This study assessed the effect of shearing around 74 days of gestation on the productive performance of ewes and lambs during the first month of life. Forty Corriedale ewes were inseminated in autumn in Southern Brazil. All ewes were kept together at the same pasture under extensive husbandry conditions. The ewes were randomly separated into two treatment groups: twenty animals were completely sheared at 74 ± 6 days of pregnancy, and twenty were kept without sheared during pregnancy, composing the control group. Ewes and their lambs were evaluated at three different times during the experiment: at birth, between 15 and 21 days post-partum and between 22 and 45 days post-partum. Ewes had their body condition score, body weight, placental weight, milk production and serum concentrations of beta-hydroxybutyrate measured, while lambs had hematocrit, hemoglobin, and plasma lactate and glucose, as well as body weight at birth and until wean determined. Values of hematocrit and hemoglobin were lower and body weight at birth and at wean was higher in the group of lambs born from sheared ewes. Placenta weight was higher in sheared ewes. Body condition score and beta-hydroxybutyrate showed no differences between groups. Milk production of sheared ewes (1.26 L/day) was higher than in control group (0.93 L/day). Shearing ewes at 74 days of pregnancy was efficient for the better development of lambs at post-birth, reducing perinatal mortality rates.

Placental adaptations in growth restriction

The placenta is the primary interface between the fetus and mother and plays an important role in maintaining fetal development and growth by facilitating the transfer of substrates and participating in modulating the maternal immune response to prevent immunological rejection of the conceptus. The major substrates required for fetal growth include oxygen, glucose, amino acids and fatty acids, and their transport processes depend on morphological characteristics of the placenta, such as placental size, morphology, blood flow and vascularity. Other factors including insulin-like growth factors, apoptosis, autophagy and glucocorticoid exposure also affect placental growth and substrate transport capacity. Intrauterine growth restriction (IUGR) is often a consequence of insufficiency, and is associated with a high incidence of perinatal morbidity and mortality, as well as increased risk of cardiovascular and metabolic diseases in later life. Several different experimental methods have been used to induce placental insufficiency and IUGR in animal models and a range of factors that regulate placental growth and substrate transport capacity have been demonstrated. While no model system completely recapitulates human IUGR, these animal models allow us to carefully dissect cellular and molecular mechanisms to improve our understanding and facilitate development of therapeutic interventions.

Effects of maternal dexamethasone treatment early in pregnancy on glucocorticoid receptors in the ovine placenta

The effects of endogenous cortisol on binucleate cells (BNCs), which promote fetal growth, may be mediated by glucocorticoid receptors (GRs), and exposure to dexamethasone (DEX) in early pregnancy stages of placental development might modify this response. In this article, we have investigated the expression of GR as a determinant of these responses. Pregnant ewes carrying singleton fetuses (n = 119) were randomized to control (2 mL saline/ewe) or DEX-treated groups (intramuscular injections of 0.14 mg/kg ewe weight per 12 hours) at 40 to 41 days of gestation (dG). Placental tissue was collected at 50, 100, 125, and 140 dG. Total glucocorticoid receptor protein (GRt) was increased significantly by DEX at 50 and 125 dG in females only, but decreased in males at 125 dG as compared to controls. Glucocorticoid receptor α (GRα) protein was not changed after DEX treatment. Three BNC phenotypes were detected regarding GRα expression (++, +-, --), DEX increased the proportion of (++) and decreased (--) BNC at 140 dG. Effects were sex- and cell type dependent, modifying the responsiveness of the placenta to endogenous cortisol. We speculate that 3 maturational stages of BNCs exist and that the overall activity of BNCs is determined by the distribution of these 3 cell types, which may become altered through early pregnancy exposure to elevated glucocorticoids.

Early dexamethasone treatment induces placental apoptosis in sheep

Glucocorticoid treatment given in late pregnancy in sheep resulted in altered placental development and function. An imbalance of placental survival and apoptotic factors resulting in an increased rate of apoptosis may be involved. We have now investigated the effects of dexamethasone (DEX) in early pregnancy on binucleate cells (BNCs), placental apoptosis, and fetal sex as a determinant of these responses. Pregnant ewes carrying singleton fetuses (n = 105) were randomized to control (n = 56, 2 mL saline/ewe) or DEX treatment (n = 49, intramuscular injections of 0.14 mg/kg ewe weight per 12 hours over 48 hours) at 40 to 41 days of gestation (dG). Placentomes were collected at 50, 100, 125, and 140 dG. At 100 dG, DEX in females reduced BNC numbers, placental antiapoptotic (proliferating cell nuclear antigen), and increased proapoptotic factors (Bax, p53), associated with a temporarily decrease in fetal growth. At 125 dG, BNC numbers and apoptotic markers were restored to normal. In males, ovine placental lactogen-protein levels after DEX were increased at 50 dG, but at 100 and 140 dG significantly decreased compared to controls. In contrast to females, these changes were independent of altered BNC numbers or apoptotic markers. Early DEX was associated with sex-specific, transient alterations in BNC numbers, which may contribute to changes in placental and fetal development. Furthermore, in females, altered placental apoptosis markers may be involved.

Regulation of placental nutrient transport and implications for fetal growth

Fetal macronutrient requirements for oxidative metabolism and growth are met by placental transport of glucose, amino acids, and, to a lesser extent that varies with species, fatty acids. It is becoming possible to relate the maternal–fetal transport kinetics of these molecules in vivo to the expression and distribution of specific transporters among placental cell types and subcellular membrane fractions. This is most true for glucose transport, although apparent inconsistencies among data on the roles and relative importance of the predominant placenta glucose transporters, GLUT-1 and GLUT-3, remain to be resolved. The quantity of macronutrients transferred to the fetus from the maternal bloodstream is greatly influenced by placental metabolism, which results in net consumption of large amounts of glucose and, to a lesser extent, amino acids. The pattern of fetal nutrient supply is also altered considerably by placental conversion of glucose to lactate and, in some species, fructose, and extensive transamination of amino acids. Placental capacity for transport of glucose and amino acids increases with fetal demand as gestation advances through expansion of the exchange surface area and increased expression of specific transport molecules. In late pregnancy, transport capacity is closely related to placental size and can be modified by maternal nutrition. Preliminary evidence suggests that placental expression and function of specific transport proteins are influenced by extracellular concentrations of nutrients and endocrine factors, but, in general, the humoral regulation of placental capacity for nutrient transport is poorly understood. Consequences of normal and abnormal development of placental transport functions for fetal growth, especially during late gestation, and, possibly, for fetal programming of postnatal disorders, are discussed.

Adipose tissue and fetal programming

Adipose tissue function changes with development. In the newborn, brown adipose tissue (BAT) is essential for ensuring effective adaptation to the extrauterine environment, and its growth during gestation is largely dependent on glucose supply from the mother to the fetus. The amount, location and type of adipose tissue deposited can also determine fetal glucose homeostasis. Adipose tissue first appears at around mid-gestation. Total adipose mass then increases through late gestation, when it comprises a mixture of white and brown adipocytes. BAT possesses a unique uncoupling protein, UCP1, which is responsible for the rapid generation of large amounts of heat at birth. Then, during postnatal life some, but not all, depots are replaced by white fat. This process can be utilised to investigate the physiological conversion of brown to white fat, and how it is re-programmed by nutritional changes in pre- and postnatal environments. A reduction in early BAT deposition may perpetuate through the life cycle, thereby suppressing energy expenditure and ultimately promoting obesity. Normal fat development profiles in the offspring are modified by changes in maternal diet at defined stages of pregnancy, ultimately leading to adverse long-term outcomes. For example, excess macrophage accumulation and the onset of insulin resistance occur in an adipose tissue depot-specific manner in offspring born to mothers fed a suboptimal diet from early to mid-gestation. In conclusion, the growth of the different fetal adipose tissue depots varies according to maternal diet and, if challenged in later life, this can contribute to insulin resistance and impaired glucose homeostasis.

Effects of rumen-protected methionine on plasma amino acid concentrations during a period of weight loss for late gestating beef heifers

This study determined changes in plasma amino acid concentration in late-gestating (beginning 58 ± 1.02 days prior to calving), primiparous, winter-grazing range heifers receiving wheat middling-based supplement without (CON) or with rumen-protected methionine (MET) to provide 15 g DL-MET each day. Plasma was collected on days -2 and 0 (start of MET supplementation just prior to individually receiving supplement at 0700 hours). Plasma was sampled again on days 40, 42 and 44 prior to supplementation at 0700 and 1100 hours (4 h after receiving daily supplement). Data were analyzed with cow as the experimental unit. Continuous variables were analyzed by the main effects of treatment, date, or time and their interaction when appropriate. Comparable BW (P = 0.32) and BCS (P = 0.83) over the 44-day metabolism trial were found between both CON- and MET-fed heifers. MET-supplemented heifers had greater (P < 0.01) plasma concentrations of methionine indicating that the rumen-protection technology successfully delivered methionine to the small intestine. Supplementation with rumen-protected DL-MET caused a significant supplement × date interaction for glutamine (P = 0.03), glycine (P = 0.02), methionine (P < 0.01), and serine (P = 0.05). In addition, trends for supplement × date interactions were detected for leucine (P = 0.07), threonine (P = 0.09), valine (P = 0.08), total amino acids (TAA; P = 0.08), non essential amino acids (NEAA; P = 0.08), branched chain amino acids (BCAA; P = 0.08), and glucogenic amino acids (GLUCO; P = 0.08). These results suggest that the BCAA (leucine and valine) were utilized more efficiently with MET supplemented heifers compared to CON supplemented heifers. Plasma AA concentrations for glutamic acid (P < 0.01), histidine (P = 0.01), tyrosine (P < 0.01), and EAA (P < 0.01), all decreased throughout the study. These results further confirm methionine is a limiting amino acid in forage fed late-gestating heifers and further suggests the limitation when grazing dormant range forages as shown by improved utilization of other plasma amino acids when supplemental methionine was provided.

Health management of ewes during pregnancy

The objectives of health management of ewes during pregnancy are as follows: (i) successful completion of pregnancy at term, (ii) birth of healthy and viable lambs, with optimal birth and potential weaning bodyweight, (iii) optimum milk production during the subsequent lactation and (iv) improved management in relation to drug residues in animal products. Knowledge of the physiological background of pregnancy in ewes: changes, mechanisms and interactions, during pregnancy is important for the overall health management of ewes during pregnancy. Health management of pregnant ewes includes diagnosis of pregnancy and evaluation of the number of foetuses borne, which will support strategies for subsequent management of the flock. Nutritional management of ewes depends upon the stage of lactation and specifically aims to (i) prevention of pregnancy toxaemia and other metabolic diseases during the peri-partum period, (ii) formation of colostrum in appropriate quantity and quality, (iii) production of lambs with normal future birth bodyweight and (iv) support of increased milk yield during the subsequent lactation. At the end of lactation, udder management of pregnant ewes includes its clinical examination, culling of ewes considered unsuitable for lactation and, possibly, the intramammary administration of antibiotics; objectives of that procedure are (i) to cure infections which have occurred during the previous lactation and (ii) to prevent development of new mammary infection during the dry period. Management of abortions includes the correct and timely diagnosis of the causative agent of the disorder, as well as the strategic administrations of chemotherapeutic agents, aiming to prevent abortions in flocks with confirmed infection with an abortifacient agent, especially if no appropriate vaccinations had been carried out before the mating season. During the final stage of pregnancy, health management of ewes includes administration of appropriate anthelmintic drugs, aiming to eliminate gastrointestinal helminthes (thus, increasing production output of ewes) and preventing the built-up of parasitic burdens in the environment (thus, reducing infection of lambs during their neonatal period). Vaccinations of pregnant ewes aim to protect these animals, as well as their offspring, especially against diseases which are a frequent cause of neonatal mortality (e.g., clostridial infections). Health management also aims to prevent the main metabolic disorders of pregnant ewes (i.e., pregnancy toxaemia and hypocalcaemia), as well as to monitor flocks for development of these disorders. Health management of pregnant ewes is completed with application of husbandry practices before the start of the lambing season. Finally, in some cases, health management may include induction and synchronisation of lambings, which is a management or therapeutic procedure.

Decreasing maternal nutrient intake during the final third of pregnancy in previously overnourished adolescent sheep: effects on maternal nutrient partitioning and feto-placental development

When pregnant adolescent sheep are overnourished during pregnancy normal nutrient partitioning priorities to the gravid uterus are altered, leading to impaired placental development and fetal growth restriction. We hypothesized that decreasing dietary intake in overnourished dams during the final third of gestation may reverse this inappropriate nutrient partitioning in favor of the fetus. Adolescent ewes were offered control (C; n = 12) or high (H; n = 20) dietary intakes to induce normal vs. compromised placental development. Ten ewes receiving the H intake were switched to a low intake at d90 of gestation (HL). Between d90 to 130, HL dams lost weight and adiposity, and metabolic hormones and glucose at d130 were less than H and similar to C. In spite of these maternal changes, at d130 fetal bodyweight was equivalent in HL and H groups and ∼20% less than in C. A greater degree of brain sparing was evident in HL fetuses and glucose and insulin concentrations were more perturbed than in H fetuses. Relative to C, placentome weight was reduced by 46 and 32% in H and HL and the fetal:placentome weight ratio was H > HL > C. Placental vascular morphology was largely unaffected by maternal diet during late gestation but mRNA expression of five angiogenic genes was up-regulated in the fetal cotyledon of HL pregnancies, commensurate with blood vessel remodeling. Nevertheless, overfeeding to promote maternal anabolic growth during adolescent pregnancy impairs feto-placental development that cannot be rescued by reducing maternal intake during the final third of gestation.

Ovine surgical model of uterine space restriction: interactive effects of uterine anomalies and multifetal gestations on fetal and placental growth

Intrauterine growth restriction (IUGR) is observed in conditions with limitations in uterine space (e.g., uterine anomalies and multifetal gestations). IUGR is associated with reduced fetal weight, organ growth, and a spectrum of adult-onset diseases. To examine the interaction of uterine anomalies and multifetal gestations, we developed a surgical uterine space restriction model with a unilateral uterine horn ligation before breeding (unilateral surgery). Placentas and fetuses were studied on Gestational Day (GD) 120 and GD 130 (term = 147 days). Unilateral surgery decreased placentome numbers in singleton and twin pregnancies (25% and 50%, respectively) but not unilateral triplets. Unilateral surgery decreased total placentome weight in twin pregnancies (decreased 24%). Fetuses categorized as uterine space restricted (unilateral twin and both groups of triplets) had 51% fewer placentomes per fetus and a 31% reduction in placentomal weight per fetus compared to the nonrestricted group (control singleton, unilateral singleton, and control twin). By GD 130, uterine space-restricted fetuses exhibited decreased weight, smaller crown-rump, abdominal girth, and thoracic girth as well as decreased fetal heart, kidney, liver, spleen, and thymus weights. Lung and brain weights were unaffected, demonstrating asymmetric IUGR. At GD 130, placental efficiency (fetal weight per total placentomal weight) was elevated in uterine space-restricted fetuses. However, fetal arterial creatinine, blood urea nitrogen, and cholesterol were elevated, suggesting insufficient placental clearance. Maternal-to-fetal glucose and triglycerides ratios were elevated in the uterine space-restricted pregnancies, suggesting placental nutrient transport insufficiency. This model allows for examination of interactive effects of uterine space restriction-induced IUGR on placental adaptation and fetal organ growth.

Effects of a Streptococcus equi infection-mediated nutritional insult during mid-gestation in primiparous Thoroughbred fillies. Part 1: Placental and fetal development

REASONS FOR PERFORMING STUDY

There is a paucity of information on factors that influence placental development in the horse.

HYPOTHESIS

Changes in nutrition, particularly around the time of proliferative placental growth, can affect development of the placenta and fetal growth.

OBJECTIVE

To investigate the effects of 2 planes of nutrition and an unforeseen infection-mediated nutritional insult on placental and fetal development in the mare.

METHODS

Twenty maiden Thoroughbred fillies, age 3 or 4 years, mated to one Thoroughbred stallion, were maintained on either High or Moderate food intake throughout pregnancy. In mid-gestation all the mares unexpectedly became infected with Streptococcus equi and suffered varying degrees of weight loss as a consequence. Gross and stereological measurements of the placenta and measurements of foal birthweight, crown-rump length, ponderal index and plasma IGF-1 concentration were made at term.

RESULTS

Gains in bodyweight during gestation were significantly higher in the High vs. the Moderate nutrition groups. Placental and fetal growth parameters were not influenced by the plane of nutrition. However, transient weight loss in mid-gestation from acutely reduced food intake resulted in morphological changes to the allantochorion and decreased foal birthweight.

CONCLUSIONS

Excessive weight gain during gestation in maiden Thoroughbred fillies does not result in nutrient partitioning to the dam at the expense of the fetus. However, sudden weight loss in mid-gestation has detrimental effects on placental development which results in reduced fetal growth.

POTENTIAL RELEVANCE

Clinicians should appreciate the likely effects of maternal infection and resulting weight loss on pregnancy outcome.

C-type natriuretic peptide forms in pregnancy: maternal plasma profiles during ovine gestation correlate with placental and fetal maturation

Circulating concentrations of C-type natriuretic peptide (CNP) and a related amino terminal fragment (NTproCNP) were measured at weekly intervals from preconception to 3 wk postpartum in ewes with twins (n = 8) and nonpregnant ewes (n = 8). In contrast to low and stable values in nonpregnant ewes (CNP, 0.75 +/- 0.08; NTproCNP, 22 +/- 2 pmol/liter), CNP forms increased abruptly at 40-50 d of gestation and rose to peak values (CNP, 31 +/- 5, NTproCNP, 270 +/- 16 pmol/liter) at about d 120. Approximately 7 d prepartum, the concentration of both CNP forms fell precipitously to preconception values immediately postpartum. In separate studies, circulating maternal CNP forms were positively related to fetal number at d 120. Consistent with a major contribution from the placenta to circulating levels, the concentrations of CNP forms were elevated in the placentome (cotyledon: CNP, 18 +/- 4, NTproCNP, 52 +/- 10 pmol/g; caruncle: CNP, 13 +/- 3, NTproCNP, 31 +/- 6 pmol/g) and much higher than those of intercaruncular uterine tissue (CNP, 0.19 +/- 0.05, NTproCNP, 0.98 +/- 0.2 pmol/g) in late-gestation ewes (P < 0.001, n = 4). These distinctive patterns of maternal plasma CNP forms, positive relation with fetal number, and greatly elevated protein concentrations in the placentome demonstrate the hormone's strong relation to placental and fetal maturation. The findings provide a firm basis for future studies of the functional role of CNP in fetal-maternal welfare.

Nutritional paradigms of ovine fetal growth restriction: Implications for human pregnancy

Low birth weight and prematurity are associated with short inter-pregnancy intervals, low pre-pregnancy weights, insufficient maternal weight gains during pregnancy, multifetal pregnancies and a young maternal age. Improvements in maternal nutritional status are arguably imperative for ensuring an appropriate pregnancy outcome in these vulnerable groups, but ethical boundaries limit these investigations. Experimental paradigms using the pregnant sheep have been widely used to identify the nutritionally sensitive periods of conceptus development. In adult sheep, severe undernutrition during the periconceptual period accelerates maturation of the fetal hypothalamic-pituitary adrenal axis and results in pre-term delivery. Low pre-pregnancy weight, followed by undernutrition during mid-pregnancy, results in reduced placental growth and lower birth weights at term. Studies that have restricted nutrients during mid-gestation only reveal variable effects on the placental and fetal growth trajectory, however if undernutrition is prolonged during late-pregnancy, fetal growth is compromised, particularly in twin pregnancies. In contrast, overnourishing the adolescent sheep to promote rapid maternal growth, results in the premature delivery of low birth weight lambs. These effects are mediated by impaired placental growth, uteroplacental blood flows and fetal nutrient uptakes. At the other end of the nutritional spectrum, undernourishing the adolescent sheep to gradually deplete nutrient reserves, results in fetal growth restriction which is independent of alterations in placental mass.

Early rapid growth, early birth: accelerated fetal growth and spontaneous late preterm birth

The past two decades in the United States have seen a 24% rise in spontaneous late preterm delivery (34-36 weeks) of unknown etiology. This study tested the hypothesis that fetal growth was identical prior to spontaneous preterm (n = 221, median gestational age at birth 35.6 weeks) and term (n = 3706) birth among pregnancies followed longitudinally in Santiago, Chile. The hypothesis was not supported: Preterm-delivered fetuses were significantly larger than their term-delivered peers by mid-second trimester in estimated fetal weight, head, limb, and abdominal dimensions, and they followed different growth trajectories. Piecewise regression assessed time-specific differences in growth rates at 4-week intervals from 16 weeks. Estimated fetal weight and abdominal circumference growth rates slowed at 20 weeks among the preterm-delivered, only to match and/or exceed their term-delivered peers at 24-28 weeks. After an abrupt growth rate decline at 28 weeks, fetuses delivered preterm did so at greater population-specific sex and age-adjusted birth weight percentiles than their peers from uncomplicated pregnancies (P < 0.01). Growth rates predicted birth timing: one standard score of estimated fetal weight increased the odds ratio for late preterm birth from 2.8 prior to 23 weeks, to 3.6 (95% confidence interval, 1.82-7.11, P < 0.05) between 23 and 27 weeks. After 27 weeks, increasing size was protective (OR: 0.56, 95% confidence interval, 0.38-0.82, P = 0.003). These data document, for the first time, a distinctive fetal growth pattern across gestation preceding spontaneous late preterm birth, identify the importance of mid-gestation for alterations in fetal growth, and add perspective on human fetal biological variability.

Identifying when weather influences life-history traits of grazing herbivores

1. There is increasing evidence that density-independent weather effects influence life-history traits and hence the dynamics of populations of animals. Here, we present a novel statistical approach to estimate when such influences are strongest. The method is demonstrated by analyses investigating the timing of the influence of weather on the birth weight of sheep and deer. 2. The statistical technique allowed for the pattern of temporal correlation in the weather data enabling the effects of weather in many fine-scale time intervals to be investigated simultaneously. Thus, while previous studies have typically considered weather averaged across a single broad time interval during pregnancy, our approach enabled examination simultaneously of the relationships with weekly and fortnightly averages throughout the whole of pregnancy. 3. We detected a positive effect of temperature on the birth weight of deer, which is strongest in late pregnancy (mid-March to mid-April), and a negative effect of rainfall on the birthweight of sheep, which is strongest during mid-pregnancy (late January to early February). The possible mechanisms underlying these weather-birth weight relationships are discussed. 4. This study enhances our insight into the pattern of the timing of influence of weather on early development. The method is of much more general application and could provide valuable insights in other areas of ecology in which sequences of intercorrelated explanatory variables have been collected in space or in time.

An immunohistochemical study of the localization and developmental expression of ghrelin and its functional receptor in the ovine placenta

BACKGROUND

Ghrelin is an orexigenic hormone principally produced by the stomach, but also by numerous peripheral tissues including the placenta. Ghrelin acts via growth hormone secretagogue receptors (GHSR-1a) to alter food intake, fat utilization, and cellular proliferation, and has been suggested to play a role in the developmental growth of the fetoplacental unit. The placental expression of ghrelin and its role in ruminant species is not known. We tested the hypotheses that ghrelin and its functional receptor, GHSR-1a, are present in tissues of the ovine placenta, and that their expression is linked to the stage of development.

METHODS

Antibodies raised against ghrelin and GHSR-1a were used in standard immunohistochemical protocols on placental tissues collected from pregnant ewes (n = 6 per gestational time point) at days 50, 80, 100, 128 and 135 of gestation (term approximately day 145). Immunostaining for ghrelin and GHSR-1a was quantified using computer-aided image analysis. Image analysis data were subjected to one-way ANOVA, with differences in immunostaining between time-points determined by Fisher's least significant difference.

RESULTS

Positive immunostaining for ghrelin was detected in ovine placentae at all gestational time points, with staining localized to the maternal epithelium, caruncle and trophectoderm. There was a significant effect of gestational age (p < 0.001) on the placental expression of ghrelin, with maximal levels at gestational day 80. GHSR-1a immunostaining was detected in the fetal trophectoderm at all time points. In contrast to the gestational pattern of ghrelin expression, there was no effect of gestational age on placental GHSR-1a immunoexpression.

CONCLUSION

Ghrelin and GHSR-1a are both present in the ovine placenta, and ghrelin displays a developmentally-related pattern of expression. Therefore, these data strongly suggest that the ghrelin system may have a role in feto-placental development in sheep.

Placental growth, angiogenic gene expression, and vascular development in undernourished adolescent sheep

Limiting maternal nutrient intake during ovine adolescent pregnancy progressively depleted maternal body reserves, impaired fetal nutrient supply, and slowed fetal soft tissue growth. The present study examined placental growth, angiogenic gene expression, and vascular development in this undernourished adolescent model at Days 90 and 130 of gestation. Singleton pregnancies were established, and ewes were offered an optimal control (C; n = 14) or low (L [0.7 x C]; n = 21) dietary intake. Seven ewes receiving L intakes were switched to C intakes on Day 90 of gestation (L-C). Fetal body weight (P < 0.01) and glucose concentrations (P < 0.03) were reduced in L versus C pregnancies by Day 130, whereas L-C group values were intermediate. Placental cellular proliferation, gross morphology, and mass were independent of maternal nutrition at both Day 90 and 130. In contrast, capillary area density in the maternal caruncular portion of the placentome was reduced by 20% (P < 0.001) at both stages of gestation in L compared with C groups. Caruncular capillary area density was equivalent in the L and L-C groups at Day 130. Placental mRNA expression of five key angiogenic ligands or receptors increased (P < 0.001) between Days 90 and 130 of gestation. VEGFA mRNA expression was higher (P < 0.04) in L compared with C and L-C pregnancies at Day 130, but otherwise gene expression of the remaining angiogenic factors and receptors analyzed was unaffected by maternal intake. Undernourishing the pregnant adolescent dam restricts fetal growth independently of changes in placental mass. Alterations in maternal placental vascular development may, however, play a role in mediating the previously reported reduction in maternal and hence fetal nutrient supply.

Effect of diet composition on pregnancy outcome in overnourished rapidly growing adolescent sheep

When pregnant adolescent sheep are overnourished to promote maternal growth during pregnancy, growth of the placenta is impaired and results in the premature delivery of low birth weight lambs relative to control-fed adolescents of equivalent age. These effects have been achieved by feeding two levels of the same complete diet. The present study evaluated the role of protein in pregnancy outcome in our adolescent sheep paradigm. Adolescent ewes were implanted with single embryos on day 4 post-oestrus. Thereafter ewes were offered ad libitum an isoenergetic diet (11·4 MJ metabolisable energy/kg DM) containing either 12 % (basic, B) or 17 % (extra, E) crude protein. At day 75 of gestation, half the pregnant ewes on each protein level were switched to yield four groups, BB, EE, BE and EB protein. A further optimally nourished control group received a moderate quantity of a ration (14 % crude protein) designed to provide 100 % of the estimated energy and protein requirement of the adolescent sheep according to stage of pregnancy. Pregnancy outcome was determined at term. Feed intakes were independent of protein level in the four groups of ewes fed ad libitum and were higher (P < 0·001) than in the control group throughout. Maternal plasma urea concentrations reflected the current crude protein content of the diet offered and were elevated in the 17 % compared with 12 % protein groups (P < 0·001). Within groups fed ad libitum, maternal plasma insulin, glucose, NEFA and homocysteine concentrations were largely independent of protein level. Gestation length, placental weight, lamb birth weight and initial colostrum yield were reduced (P < 0·05) in all groups fed ad libitum relative to the optimally nourished control group. Similarly, total colostrum IgG, butterfat, lactose and crude protein content at parturition were attenuated in the ad libitum compared with the control groups. However, within ad libitum groups pregnancy outcome parameters were largely unaffected by level or timing of exposure to high protein intakes. The data imply that it is high-energy intakes that are the primary cause of impaired placental development and adverse pregnancy outcome in rapidly growing adolescent sheep.

Long-term effects of nutritional programming of the embryo and fetus: mechanisms and critical windows

The maternal nutritional and metabolic environment is critical in determining not only reproduction, but also long-term health and viability. In the present review, the effects of maternal nutritional manipulation at defined stages of gestation coinciding with embryogenesis, maximal placental or fetal growth will be discussed. Long-term outcomes from these three developmental windows appear to be very different, with brain and cardiovascular function being most sensitive to influences in the embryonic period, the kidney during placental development and adipose tissue in the fetal phase. In view of the similarities in fetal development, number and maturity at birth, there are close similarities in these outcomes between findings from epidemiological studies in historical human cohorts and nutritional manipulation of large animals, such as sheep. One key nutrient that may modulate the long-term metabolic effects is the supply of glucose from the mother to the fetus, because this is sensitive to both global changes in food intake, maternal glucocorticoid status and an increase in the carbohydrate content of the diet. The extent to which these dietary-induced changes may reflect epigenetic changes remains to be established, especially when considering the very artificial diets used to induce these types of effects. In summary, the maintenance of a balanced and appropriate supply of glucose from the mother to the fetus may be pivotal in ensuring optimal embryonic, placental and fetal growth. Increased or decreased maternal plasma glucose alone, or in conjunction with other macro- or micronutrients, may result in offspring at increased risk of adult diseases.

Placentomal differentiation may compensate for maternal nutrient restriction in ewes adapted to harsh range conditions

Maternal nutrient restriction from early to midgestation can lead to fetal growth retardation, with long-term impacts on offspring growth, physiology, and metabolism. We hypothesized that ewes from flocks managed under markedly different environmental conditions and levels of nutrition might differ in their ability to protect their own fetus from a bout of maternal nutrient restriction. We utilized multiparous ewes of similar breeding, age, and parity from 2 flocks managed as 1) ewes adapted to a nomadic existence and year-long, limited nutrition near Baggs, WY (Baggs ewes), and 2) University of Wyoming ewes with a sedentary lifestyle and continuous provision of more than adequate nutrition (UW ewes). Groups of Baggs ewes and UW ewes were fed 50 (nutrient restricted) or 100% (control fed) of National Research Council recommendations from d 28 to 78 of gestation, then necropsied, and fetal and placental data were obtained. Although there was a marked decrease (P < 0.05) in fetal weight and blood glucose concentrations in nutrient-restricted vs. control fed UW ewes, there was no difference in these fetal measurements between nutrient-restricted and control-fed Baggs ewes. Nutrient-restricted and control-fed UW ewes exhibited predominantly type A placentomes on d 78, but there were fewer (P c0.05) type A and greater (P < 0.05) numbers of type B, C, and D placentomes in nutrient-restricted than control-fed Baggs ewes. Placental efficiency (fetal weight/placentomal weight) was reduced (P = 0.04) in d 78 nutrient-restricted UW ewes when compared with control-fed UW ewes. In contrast, nutrient-restricted and control-fed Baggs ewes exhibited similar placental efficiencies on d 78. This is the first report of different placental responses to a nutritional challenge during pregnancy when ewes were selected under different management systems. These data are consistent with the concept that Baggs ewes or their conceptuses, which were adapted to both harsh environments and limited nutrition, initiated conversion of type A placentomes to other placentomal types when subjected to an early to mid-gestational nutrient restriction, whereas this conversion failed to occur in UW ewes. This early placentomal conversion in the Baggs ewes may function to maintain normal nutrient delivery to their developing fetuses during maternal nutrient restriction.

Altered placental and fetal expression of IGFs and IGF-binding proteins associated with intrauterine growth restriction in fetal sheep during early and mid-pregnancy

The insulin-like growth factors (IGFs) are postulated to be altered in association with the development of intrauterine growth restriction (IUGR). The present studies examined placental and fetal hepatic mRNA concentration of components of the IGF system at two time points (55 and 90 d gestational age, dGA; Term 147 dGA) in a hyperthermia (HT)-induced sheep model of placental insufficiency-IUGR. Maternal plasma insulin and IGF-I were constant at 55 and 90 dGA and were unaffected by treatment. Umbilical vein insulin concentrations tended to be reduced at 90 dGA following HT exposure. Caruncle IGF-I mRNA was increased at 90 dGA in HT placentae (p < 0.05), while cotyledon concentrations were constant over gestation and unaltered by treatment. In control cotyledons, IGF-II mRNA concentration increased (p < 0.01) and IGFBP-3 decreased between 55 and 90 dGA (p < 0.01). Cotyledon IGF-II and caruncle IGFBP-4 mRNA were elevated at 55 dGA in HT placentae compared with control (p < 0.01 and p < 0.05 respectively). Fetal hepatic IGF-I, IGFBP-2, -3 and -4 concentrations rose over gestation (p < 0.05), but there were no treatment effects. These data suggest that changes in placental IGF expression in early and mid gestation may predispose the pregnancy to placental insufficiency, resulting in inadequate substrate supply to the developing fetus later in gestation.

Influence of the dam and sire on size at birth and subsequent growth, milk production and fertility in dairy heifers

Genetic selection has resulted in larger cows with high milk production potential but a tendency for poor fertility. In multiparous cows fetal development competes for nutrients with concurrent milk production. This study tested the hypotheses that (a) maternal age and milk yield during pregnancy alter calf birth size and (b) birth weight influences subsequent productivity and fertility. Concurrently born Holstein-Friesian heifers (n=65) with multiparous dams and three sires were monitored from birth to the end of their first lactation to assess effects of birth weight on growth, milk production and fertility. Calves were analyzed as three subgroups: low (L), average (A) and high (H) birth weight (BW) calves (n=21-22 per group). LBW calves were born 10 kg lighter than HBW calves and remained significantly lighter throughout the study. They were generally smaller in other measured indices (length, height, girth, ponderal index) between birth and 9 months and were more likely to have older dams (lactations 3-6) with higher peak yields (>42 kg/day). Milk production parameters were indistinguishable between the 3 birthweight groups and metabolic parameters (IGF-I, insulin, glucose) measured around first calving were unaffected. HBW offspring were more likely to have persistent corpora lutea following their first calving and other fertility parameters also tended to be worse. Sire influenced gestation length but not birth size. Sire heritability estimates showed that weight, IGF-I and insulin concentrations after first calving and fertility in the first lactation were all heritable. The results support the hypothesis that high milk production in the dam may predispose to birth of a smaller calf. Smaller birth size did not, however, have any subsequent adverse effects on productivity or fertility in the first lactation and sire was more influential at this stage.

Functional Significance and Cortisol Dependence of the Gross Morphology of Ovine Placentomes During Late Gestation1

The gross morphological appearance of ovine placentomes is known to alter in response to adverse intrauterine conditions that increase fetal cortisol exposure. The direct effects of fetal cortisol on the placentome morphology, however, remain unknown, nor is the functional significance of the different placentome types clear. The present study investigated the gross morphology of ovine placentomes in relation to placental nutrient delivery to sheep fetuses during late gestation and after experimental manipulation of the fetal cortisol concentration. As fetal cortisol levels rose naturally toward term, a significant decrease was observed in the proportion of the D-type placentomes that had the hemophagous zone everted over the bulk of the placentomal tissue. When the prepartum cortisol surge was prevented by fetal adrenalectomy, there were proportionately more everted C- and D-type placentomes and fewer A-type placentomes with the hemophagous zone inverted into the placentome compared with those of intact fetuses at term. Raising cortisol concentrations by infusion before term reduced the incidence of D-type placentomes and lowered the proportion of individually tagged placentomes that became more everted during the 10- to 15-day period between tagging and delivery. Cortisol, therefore, appears to prevent hemophagous zone eversion in ovine placentomes during late gestation. The distribution of placentome types appeared to have no effect on the net rates of placental delivery of glucose and oxygen to the fetus under normal conditions. When fetal cortisol levels were raised by exogenous infusion, however, placental delivery of glucose, but not oxygen, to the fetus, measured as umbilical uptake, was reduced to a greater extent in fetuses with a higher proportion of C- and D-type placentomes. The gross morphology of the ovine placentomes is, therefore, determined, at least in part, by the fetal cortisol concentration and may influence placental nutrient transfer when fetal cortisol concentrations are high during late gestation. These findings have important implications for the placental control of fetal growth and development, particularly during adverse intrauterine conditions.

Fetoplacental transport and utilization of amino acids in IUGR — a review

Amino acids have multiple functions in fetoplacental development. The supply of amino acids to the fetus involves active transport across and metabolism within the trophoblast. Transport occurs through various amino acid transport systems located on both the maternal and fetal facing membranes, many of which have now been documented to be present in rat, sheep and human placentas. The capacity of the placenta to supply amino acids to the fetus develops during pregnancy through alterations in such factors as surface area and specific time-dependent transport system expression. In intrauterine growth restriction (IUGR), placental surface area and amino acid uptakes are decreased in human and experimental animal models. In an ovine model of IUGR, produced by hyperthermia-induced placental insufficiency (PI-IUGR), umbilical oxygen and essential amino acid uptake rates are significantly reduced in the most severe cases in concert with decreased fetal growth. These changes indicate that severe IUGR is likely associated with a shift in amino acid transport capacity and metabolic pathways within the fetoplacental unit. After transport across the trophoblast in normal conditions, amino acids are actively incorporated into tissue proteins or oxidized. In the sheep IUGR fetus, however, which is hypoxic, hypoglycemic and hypoinsulinemic, there appear to be net effluxes of amino acids from the liver and skeletal muscle, suggesting changes in amino acid metabolism. Potential changes may be occurring in the insulin/IGF-I signaling pathway that includes decreased production and/or activation of specific signaling proteins leading to a reduced protein synthesis in fetal tissues. Such observations in the placental insufficiency model of IUGR indicate that the combination of decreased fetoplacental amino acid uptake and disrupted insulin/IGF signaling in liver and muscle account for decreased fetal growth in IUGR.