Changes in fetal organ weights during gestation after selection for ovulation rate and uterine capacity in swine

We hypothesized that the ability of the fetus to alter nutrient shunting and organ growth might be associated with uterine capacity. White crossbred gilts from a randomly selected control line, a line selected for ovulation rate, and a line selected for uterine capacity (UC) were unilaterally hysterectomized-ovariectomized at 160 d of age, mated at estrus, and slaughtered at 45, 65, 85, and 105 d of gestation (9 to 18 gilts for each line x day combination). Analysis of the data revealed that heart weights and fetal weights were decreased in the ovulation rate line. No significant differences were obtained in fetal, placental, or fetal organ weights between the control and UC lines. Allometric growth of organs was assessed by examination of the slopes of the relationships between fetal weights and fetal organ weights after natural log transformation. Only the relative growth of the liver differed between selection lines and was greater (P = 0.01) in the UC compared with the control line during early pregnancy (d 45 and 65). Allometric growth of the fetal brain, liver, and heart differed with day of gestation. A brain-sparing effect was greater (P < 0.01) on d 85 and 105 compared with d 45 and 65. By contrast, a heart-sparing effect was present during early gestation and disappeared in later gestation. Fetal liver weights were hypersensitive to differences in fetal weights on d 45, possibly associated with placental effects on fetal liver weight. Fetal spleen weights were proportional to fetal weights throughout gestation. These results indicate that selection for ovulation rate decreased total fetal and fetal heart weights, and that selection for UC altered the relationship between total fetal and fetal liver weights during early gestation. Results further indicate significant changes in allometric growth of organs during gestation.     

Growth and compositional changes of fetal tissues in pigs

Three hundred twenty fetuses were obtained from 33 pregnant gilts (Camborough-22, Pig Improvement Co.) to determine rates of nutrient deposition in fetal tissues and to estimate nutrient requirements for fetal growth. Pregnant gilts were fed an equal amount of a gestation diet (2.0 kg/d; as-fed basis), and were slaughtered at d 0, 45, 60, 75, 90, 102, or 110 of gestation (n = 3 to 6 per day). Fetuses were dissected into carcass and individual tissues (including gastrointestinal tract, liver, lung, heart, kidney, spleen [> or = d 75]), and partial placental collection was made for chemical analysis. Fetal tissues were weighed and analyzed for DM, ash, CP, and crude fat. Regression equations were obtained to explain the weight and compositional changes of individual tissues during gestation. Weights of the fetus, carcass, gastrointestinal tract, liver, heart, lung, and kidney increased cubically (P < 0.001), whereas brain weight increased linearly (P < 0.001) as gestation progressed. Fetal protein and fat contents increased quadratically (P < 0.001) as gestation progressed (R2 = 0.906 and 0.904, respectively). Changes in fetal protein and fat contents fit a multiphasic regression that consisted of two linear equations (P < 0.001, R2 = 0.988 and P < 0.001, R2 = 0.983, respectively), indicating that protein and fat growth accelerated after d 69 of gestation. Fetal protein and fat accretions were 0.25 and 0.06 g/d (P < 0.001) before d 69 of gestation, and increased to 4.63 and 1.09 g/d (P < 0.001) after d 69 of gestation. Protein needs for tissue protein gains increased 19-fold after d 69 of gestation. Results of this study indicate that the growth of the fetus and fetal tissues occurs at different rates during gestation and support the practice of a two-phase feeding strategy (before and after approximately d 70 of gestation) for pregnant gilts.     

Maternal and fetal influences on uterine and conceptus development in the cow: II. Blood flow and nutrient flux

Objectives of this study were to evaluate maternal and fetal influences on uterine and umbilical blood flows and nutrient fluxes of gravid uterine tissues of cows. Brahman cows with Brahman or Charolais fetuses and Charolais cows with Brahman or Charolais fetuses were used. Indwelling catheters were placed into a uterine artery and vein, an umbilical vein, and a fetal femoral artery and vein at 220 +/- .4 d after mating. Uterine and umbilical blood flows (liters/min) and net uptakes of oxygen, glucose, lactate, alpha-amino N, urea N, ammonia N, and estrone sulfate by the gravid uterus, fetus, and uteroplacenta were determined on d 227 +/- .4. Uterine blood flows in Brahman cows with Brahman (5.01) or Charolais (4.66) fetuses were similar but less (P less than .001) than in Charolais cows with Brahman (7.14) or Charolais fetuses (9.24), which differed (P less than .01). Umbilical blood flows of Charolais (3.78) were greater (P less than .01) than those of Brahman (2.29) fetuses. Rate of placental D2O clearance as well as net fetal uptake of oxygen, glucose, and alpha-amino N, gravid uterine uptake of alpha-amino N, and uteroplacental uptake of glucose and release of estrone sulfate were greater with Charolais than with Brahman fetuses. Gravid uterine oxygen uptake and estrone sulfate release and gravid uterine and uteroplacental lactate output were influenced by the interaction between cow and fetal breed. It is suggested that fetal growth may be limited by uterine blood flow and by function of the uteroplacenta, particularly in late gestation.     

Nutrition, body condition and reproduction in beef cows: fetal and placental development, and estrogens and progesterone in plasma

Mature, pregnant Hereford cows (n = 17) were used to determine the effect of nutrition and body energy reserves on fetal development, concentrations of nutrients and estrogens in placental fluids, and on progesterone, estrogens and placental lactogen in maternal plasma. On d 145 of gestation, cows were assigned by breeding date to two groups and fed to achieve either a thin (TH; n = 8) or a moderate (M; n = 9) body condition score (BCS) by d 195 of gestation. Body weights, BCS, estrogens, placental lactogen and progesterone in plasma were determined weekly between d 200 and 256 of gestation. Cows were slaughtered on d 259 +/- 1 of gestation, and amnionic and allantoic fluids were sampled and analyzed for concentrations of protein, fructose and estrogens. Body weights and BCS were less (P less than .01) for TH (419 kg; 3.7) than for M (511 kg; 5.7) cows at slaughter. Uterine weights were less (P less than .07), but chorioallantoic weights were greater (P less than .07) in TH than in M cows. Cotyledonary weights were greater (P less than .05) for TH than for M cows, and total fructose in amnionic fluid was reduced (P less than .01) in TH compared with M cows. Concentrations of estradiol, estrone and placental lactogen were greater between d 240 and 256 of gestation for TH than for M cows. We conclude that nutrient intake and(or) BCS of beef cows during late gestation influence placental weight, fructose in amnionic fluid, and placental lactogen, estrone and estradiol in plasma.     

The effect of divergent selection for uterine capacity on fetal and placental development at term in rabbits: maternal and embryonic genetic effects

The aim of this work was to study the effects of the genotype of the dam, the embryo, or their interactions on prenatal growth by performing double-reciprocal embryo transfers between two lines of rabbits divergently selected for uterine capacity. Females from high (n = 53) and low (n = 48) lines were slaughtered at 72 h of gestation, and recovered embryos were transferred to the oviducts of recipient does from the high (n = 23) and low (n = 19) lines. Each recipient doe received eight embryos from the high line into one oviduct and eight embryos from the low line into the other. Recipient does were slaughtered on d 28 of gestation. The percentages of live fetuses at 28 d of gestation were 89.2 and 74% for high and low recipient lines, respectively. Length and weight of the empty uterine horn and weight of the full uterine horn were not affected by either the recipient or by donor line. Fetal weight was affected by the recipient line but not by the donor line. Fetuses gestated in high recipient does were 7% heavier (P < 0.10) than those in the low recipient does. There was a donor and a donor x recipient interaction effect on fetal placental weight. Fetal placental weight was heavier (7%, P < 0.01) for embryos from the low line. Embryos from the high line gestated in low-line uteri showed a lower fetal placenta weight than did low-line embryos gestated in high-line uteri and low-line uteri (P < 0.05). Linear regression coefficients of fetal weight at term on fetal placental weights differed (P < 0.05) for the high and low donors (4.33 +/- 0.28 and 3.41 +/- 0.29 respectively). A significant effect of the donor genotype on individual placental length was observed (P < 0.05), which might have resulted from a smaller individual placental length of low-line embryos gestated high-line uteri (P < 0.10). Neither donor nor recipient lines affected maternal placental weight or available space for fetuses. Fetuses and their fetal placentae were heavier when receiving more than four blood vessels than when receiving less than three blood vessels (13 and 17% respectively, P < 0.05). Neither recipient nor donor genotype affected the number of blood vessels arriving at each live fetus. Thus, fetal weight depends on the maternal genotype, whereas fetal placental weight depends on the embryo genotype in these two lines of rabbits divergently selected for uterine capacity.     

Differences in placental structure during gestation associated with large and small pig fetuses

The efficiency of nutrient transport from the pregnant female pig to the developing fetus depends on the size and function of the placenta. It has been reported that maternal and fetal blood vessels are arranged in a cross-countercurrent arrangement within placental microscopic folds. Thus, the blood supplies are in close apposition to each other within these microscopic folds, and maternal and fetal blood flows in approximately opposite directions perpendicular to the plane of the placenta. This arrangement indicates that the width of the microscopic folds influences placental efficiency. The objective of this study was to determine whether differences in pig placental microscopic fold development are associated with differences in fetal size or are influenced by selection for ovulation rate or uterine capacity. Gilts from a randomly selected control line, a line selected for ovulation rate, and a line selected for uterine capacity were slaughtered, and uterine wall samples were collected within the placentas associated with the largest and smallest fetuses in each litter on d 45, 65, 85, and 105 of gestation. The uterine wall samples were processed for histology and analyzed using computer-assisted morphometry. Average width of the placental folds and average width of the placental stroma above the folds were measured. To measure fold complexity, the length of the epithelial bilayer for a given length of placenta was also measured. The width of the folded bilayer increased significantly from d 65 to 105 and was greater in placentas associated with small fetuses compared with large fetuses on d 105 of gestation. In contrast, the width of the placental stroma above the folded bilayer decreased with gestation and decreased more rapidly in placenta associated with the smallest compared with the largest fetus. These results indicate that the width of the microscopic folds of the placental trophoblast/endometrial epithelial bilayer is increased in placenta associated with small fetuses, which we hypothesize will increase the surface area for interaction between maternal and fetal blood supplies, thus improving placental efficiency in response to reduced placental size.     

Conceptus competition for uterine space: different strategies exhibited by the Meishan and Yorkshire pig

Our laboratory has demonstrated that Yorkshire placentae increase in size and surface area during the final third of gestation. In contrast, Meishan placental size remains constant during late gestation, but the density of blood vessels at the placental-endometrial interface increases markedly. Preliminary observations from our laboratory suggest that if one of two adjacent Meishan fetuses dies, the placenta of the remaining Meishan conceptus fails to increase its length of implantation or its placental weight or surface area. In contrast, if one of two adjacent Yorkshire fetuses dies, the adjacent conceptus accelerates its placental growth. The objective of this experiment was to document that Yorkshire, but not Meishan, conceptuses accelerate placental growth when adjacent fetuses are experimentally destroyed on d 40 of gestation. Straightbred Meishan (n = 5) and Yorkshire (n = 5) females were laparotomized and one uterine horn was randomly assigned to receive fetal crushing (treated horn); the other uterine horn served as a within-animal control. In the treated horn, every other fetus was then crushed through the uterine wall and the animals were allowed to recover. On d 111, animals were killed, uteri were recovered, and fetal weight, crown-rump length (CRL), placental weight, implantation site length, and placental surface area were recorded. Although there were no statistically significant differences in fetal weight or CRL observed between treated or control horns of females of either breed, there was a tendency for the fetuses in the treated uterine horn to be longer and heavier in both breeds. There were no differences in placental weight, placental surface area, or implantation site length between conceptuses in Meishan treated and control horns, which averaged 173.8+/-6.4 g, 1,162.7+/-35.9 cm2, and 19.0+/-0.4 cm, respectively. In contrast, placental weight, placental surface area, and implantation site length were increased (P < 0.05) in Yorkshire treated horns compared to Yorkshire control horns (306.1+/-26.0 g, 1,835+/-93.9 cm2, and 33.4+/-1.5 cm vs 253.7+/-13.4 g, 1,474.3+/-50.4 cm2, and 27.2+/-0.8 cm; respectively). These data confirm that Yorkshire conceptuses, but not Meishan conceptuses, accelerate placental growth when adjacent littermates perish as late as d 40 of gestation. These data indicate that differences exist in the strategies employed by Meishan and Yorkshire conceptuses in the competition for nutrients during gestation.     

Effect of chronic infusion of placental lactogen on ovine fetal growth in late gestation

To test the hypothesis that placental lactogen (PL) is a Immoral regulator of fetal growth, six singleton sheep fetuses received a continuous intravenous fusion of 1.2 mg/d of purified ovine PL (oPL) for 14 d, beginning on Day 122 of gestation. The plasma concentration of oPL was approximately four-fold higher in infused fetuses than in six control fetuses that received a continuous infusion of saline. The circulating insulin-like growth factor 1 (IGF-1) concentration was also significantly elevated in PL-infused fetuses (43.1 ± 1.7 vs. 31.9 ± 4.l ng/ml; P < 0.05). Animals were slaughtered on Day 136, and the placenta and all major fetal tissues were dissected, weighed, and subsampled for chemical analysis. Fetal weight and crown-rump length were not significantly affected by treatment; however, the aggregate weight of the brain, liver, lungs, and heart tended to be larger (85.3 ± 2.1 vs. 79.9 ± 1.5 g/kg fetus; mean ± SE, P = 0.07) and the thyroid gland was smaller (0.18 ± 0.l vs. 0.26 ± 0.02 g/kg fetus; P < 0.05) in the PL-infused fetuses. The livers of the PL-infused fetuses had also accumulated additional glycogen (13.1 ± l.7 vs. 8.4 ± 0.7 g; P < 0.05). In late gestation, PL within the fetal compartment increases fetal plasma IGF-1 concentration and hepatic glycogen deposition and may affect the growth of several vital organs.     

Maternal and fetal influences on uterine and conceptus development in the cow: I. Growth of tissues of the gravid uterus.

Objectives of this study were to evaluate maternal and fetal influences on development of gravid uterine tissues of cows. Brahman cows with Brahman or Charolais fetuses and Charolais cows with Brahman or Charolais fetuses were used. Cows were killed 232 +/- .5 or 271 +/- .7 d after mating. The gravid uterus of each cow was weighed and dissected into its component parts. Weights of the fetus, fetal membranes, cotyledons, caruncles, and uterus were recorded as were weights of the fetal liver, heart, kidneys, spleen, lungs, stomach complex, intestines, and semitendinosus muscle. Ribonucleic acid, DNA, and protein concentrations in caruncles, cotyledons, liver, heart, kidney, and semitendinosus muscle were determined. Data were analyzed by analysis of variance; breed of cow (C), breed of fetus (F), day of gestation (D), and all interactions were included in the model as fixed effects. Fetal weights were influenced (P less than .003) by C, F, D, and C x D and tended (P = .07) to be influenced by C X F X D. Weight, RNA, DNA, and protein contents of selected fetal tissues followed similar patterns of significance. Thus, both maternal and fetal genotype influenced fetal growth. Greater influences of the maternal system and interrelationships between maternal and fetal systems were observed at the latter stage of gestation. Placentomal (caruncle + cotyledon) weights were greater for Charolais than for Brahman cows (P less than .02) or fetuses (P less than .001) and were greater (P less than .01) at 271 than at 232 d. Caruncular weights followed similar patterns; however, fetal genotype was the only significant source of variation in cotyledonary weight, RNA, DNA, or protein content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of recombinant porcine somatotropin on fetal and placental growth in gilts with reduced uterine capacity

Crowded uterine conditions were induced by unilateral hysterectomy-ovariectomy (UHO) in 42 gilts to determine the effect of recombinant porcine somatotropin on fetal and placental growth. Gilts were randomly assigned across three replicates to one of three treatments: Control (C; n = 14), daily injections of 1 mL saline from d 0 to 64 of gestation, Early (E; n = 12), 5 mg of rpST/d from d 0 to 30, followed by 1 mL saline from d 31 to 64, and Late (L; n = 16), 1 mL saline/d from d 0 to 29, followed by 5 mg of rpST/d from d 30 to 64 of gestation. Blood was collected from each gilt via jugular venipuncture at d 0 and every 15 d thereafter. Gilts were hysterectomized on d 65 of gestation. Length of placental attachment and fetal crown-rump length were measured. Placentas and fetuses were weighed. Placental length, wet weight, and dry weight were recorded. Treatment with rpST (either E or L) increased (P < 0.0001) maternal plasma IGF-I concentrations relative to controls. Treatment with rpST did not affect placental wet weight or placental DNA content. However, E and L treatments increased the percentage of placental protein (P = 0.01) and placental dry matter (P = 0.10) and increased contact area of uterine-placental interface (P = 0.01). Despite changes in placental composition and morphology, weights of fetuses collected from L-treated gilts did not differ from controls, whereas weights of fetuses collected from E-treated gilts tended to be less than controls (P < 0.06). Administration of rpST increased maternal IGF-I concentrations and placental surface area but failed to increase fetal growth in the UHO model. Therefore, mechanisms that are independent of maternal IGF-I or placental contact area may control early fetal growth under crowded uterine conditions.     

The effect of dietary restriction, pregnancy, and fetal type in different ewe types on fetal weight, maternal body weight, and visceral organ mass in ewes

Our objectives were to evaluate maternal body changes in response to dietary restriction or the increased nutrient requirement of fetal growth. In Exp. 1, 28 mature crossbred ewes (61.6 +/- 1.8 kg initial BW) were fed a pelleted forage-based diet to evaluate effects of pregnancy and nutrient restriction on visceral organ mass. Treatments were arranged in 2 x 3 factorially, with dietary restriction (60% restriction vs. 100% maintenance) and reproductive status (nonpregnant [NP], d 90 or d 130 of gestation) as main effects. Dietary treatments were begun at d 50 of gestation, and restricted ewes remained at 60% of maintenance throughout the experiment. Nonpregnant and d-90 ewes were fed dietary treatments for 40 d and slaughtered. The d-130 ewes were fed dietary treatments for 80 d and then slaughtered. In Exp. 2, four Romanov ewes were naturally mated (Romanov fetus and Romanov dam; R/ R), and two Romanov embryos were transferred to each of four Columbia recipients (Romanov embryos and Columbia recipient; R/C). Three Columbia ewes were naturally mated (Columbia fetus and Columbia recipient; C/C). In both experiments, maternal organ weights were reported as fresh weight (grams), scaled to empty body weight (EBW; grams per kilogram) and maternal body weight (MBW; grams per kilogram). In Exp. 1, ewe EBW and fetal mass were decreased (P < 0.02) with restriction compared with maintenance. Dietary restriction decreased liver mass (16.7 vs. 14.5 g/kg EBW or 18.8 vs. 16.4 g/kg MBW; P < 0.01), but dietary restriction did not affect total digestive tract mass. In Exp. 2, ewe BW was less for the R/R compared with R/C and C/C (44.8 vs. 110.4 and 98.1 +/- 7.9 kg, respectively; P < 0.01). Fetal weight at d 130 was less for the R/R than for R/C and C/C (2.2 vs. 3.3 and 4.7 +/- 0.3 kg, respectively; P < 0.01) when measured as individual fetuses; however, when measured as total fetal mass carried in each ewe, there was no effect of ewe type. These data suggest that the gastrointestinal tract, along with other maternal organs, responds to both level of dietary intake and nutrient requirements for gestation, and that fetal weight is decreased as a result of a 40% decrease in nutrients offered.     

Intrauterine position effects in male and female swine: subsequent survivability, growth rate, morphology and semen characteristics

Pigs of known intrauterine position were obtained from 31 litters by a procedure in which donor sows were slaughtered at d 112 of gestation, their uteri removed and piglets delivered manually. Uterine position was recorded for each piglet as being positioned between two female fetuses (OM), between a male and female fetus (1M), between two male fetuses (2M), between a female fetus and the tip of the uterine horn (OE) or between a male fetus and the tip of the horn (1E). Piglets were fostered as litter groups to recipient sows and reared in these groups until 120 d of age. They then were regrouped and housed as groups of three and six for males and females, respectively. Intrauterine position had no effect on birth weight or survivability of pigs of either sex, although pigs positioned in utero nearest the ovaries (OE and 1E) tended to be heavier at birth. Body weights were similar among groups in each sex at 120 and 175 d of age when given ad libitum access to feed; however, 2M males gained more weight from d 175 to 270 under restricted feeding conditions (P less than .05). Intrauterine position had no effect on anogenital distances either at birth or 120 d of age, and predicted testes weights were similar among males from different positions. Semen characteristics at 220 d of age did not appear to vary due to prenatal environment. Although volume tended to be less for 0M males (P less than .12), concentration, motility and sperm/ejaculate were similar among groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

The impacts of uterine environment and fetal genotype on conceptus size and placental vascularity during late gestation in pigs.

Meishan and Yorkshire gilts were bred exclusively to Yorkshire and Meishan boars, respectively, resulting in similar Meishan x Yorkshire fetuses gestating in the uteri of both maternal breeds. Gilts of both breeds were slaughtered on d 90 and 110 of gestation, and the weight and volume of each uterine horn was determined. Fetal weights and crown-rump lengths were recorded. A section of the chorioallantoic-endometrial attachment site was collected for each conceptus and evaluated for placental and endometrial vascular density. An intact placenta was recovered for each conceptus and weighed, and its surface area was determined. Fetal weight and crown-rump length increased (P < .001) markedly between d 90 and 110 of gestation in Meishan and in Yorkshire uteri, but they were markedly less (P < .001) in Meishan than in Yorkshire uteri. Placental weight and placental surface area were reduced by 40% in Meishan, compared with Yorkshire, uteri; however, placental size did not increase between d 90 and 110 in either uterine type. Placental vascular density and associated endometrial vascular density were similar (P > .20) for conceptuses in Meishan and Yorkshire uteri on d 90 and 110 of gestation. Additionally, even though the ratio of fetal weight: placental weight (placental efficiency) increased between d 90 and 110, placental efficiency was similar for conceptuses in Meishan and Yorkshire uteri. In a previous study using straightbred Meishan or Yorkshire conceptuses gestated in either a Meishan or Yorkshire uterus, we found Meishan conceptuses had a markedly greater placental efficiency than did Yorkshire conceptuses, regardless of the type of uterus in which they were gestated. These data indicate that uterine type determines conceptus size and conceptus genotype controls placental efficiency.     

The relationship of fetal weight to serum albumin and alpha-fetoprotein in swine

The within-litter relationship of fetal weight to fetal serum albumin and alpha-fetoprotein (AFP) was investigated at d 30 to 40, 45 to 50, 50 to 60, 75 to 85 and 90 to 105 of gestation in swine. Regression equations were calculated on individual litters and regression coefficients pooled across litters within each gestational age group. Coefficients for the regression of albumin on fetal weight (microgram . ml-1 . g fetus-1) were significant over all groups and ranged from 22.5 +/- 6.6 to d 45 to 50 to .7 +/- .2 at d 95 to 105. There was no significant relationship between AFP levels and fetal weight at any gestational age. Unilateral ovariectomy-hysterectomy was performed before mating to study effects of uterine crowding on the relationship of fetal weight to AFP and albumin. Although the total number of ovulations was not different from controls, this treatment resulted in only about 1.3 more fetuses/uterine horn compared with controls at either d 40 or 60 of gestation. Fetal weights in crowded litters were not different from controls. However, AFP levels in fetuses from crowded litters were lower than in control fetuses at d 40 (4.5 +/- .1 vs 6.7 +/- .5 mg/ml). Albumin levels in crowded fetuses were significantly lower than in controls at d 60 (342 +/- 50 vs 653 +/- 41 micrograms/ml). Because none of these differences in albumin or AFP could be attributed to variation in fetal weight or fetal number at the time of sample collection, it is possible that more extreme uterine crowding earlier in development resulted in these differences. These results demonstrate that fetal serum albumin concentrations are related to fetal weight when analyzed on a within-litter basis and that unilateral ovariectomy-hysterectomy may affect serum concentrations of both AFP and albumin early in fetal development. Future studies involving the regulation of synthesis of these proteins at the cellular level during development should provide information as to how factors affecting overall fetal growth and development influence the expression of a single gene. Previously, such markers that are amenable to study early in development have been lacking.     

A comparative study of ovine placental lactogen and prolactin secretion patterns in genetically dissimilar fetal co-twins

Simultaneous fetal and maternal ovine placental lactogen (oPL) and prolactin (oPRL) measurements were determined from blood samples collected from six mixed breed (MB; gestation = 141.5 +/- .7 d) pregnancies and single Rambouillet (n = 2; Ra gestation = 148 and 149 d) and Finnish Landrace (n = 2; Finn gestation = 141 and 143 d) pregnancies for the purpose of examining a possible relationship between fetal-maternal oPL and oPRL levels in the prepartal period. The MB pregnancies were produced by embryo transfer and consisted of genetically different fetuses co-existing in a common uterine environment. Despite the apparent prematurity of Ra co-twins in MB pregnancies, similar oPL and oPRL patterns during the final 14 d of gestation were observed for both Ra and Finn co-twins. Fetal oPL levels decreased at parturition (range 23 to 90 ng/ml) to approximately 60% of values recorded 8 d prepartum (range 100 to 150 ng/ml) in both fetal siblings. Increases in fetal oPRL concentrations, first observed at approximately 4 d prepartum in all fetuses, reached peak concentrations (40 to 60 ng/ml) at term. Results of this study suggest a similarity in regulation of fetal oPL and oPRL secretion, despite genetic differences for gestation period, in fetuses in the M.B. pregnancy.     

Interrelationships among conceptus size, uterine protein secretion, fetal erythropoiesis, and uterine capacity

The interrelationships among d-11 conceptus size, d-105 placental weight, placental efficiency (the ability of the placenta to support fetal growth and development), fetal erythropoiesis, and uterine capacity were examined in 1/2 Meishan, 1/2 White crossbred gilts that were unilaterally ovariohysterectomized at 90 to 100 d of age. In Exp. 1, gilts were mated after at least one normal estrous cycle and then 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 Exp. 2, 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 was recorded and the uterine horn was flushed with minimal essential medium. 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 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 average conceptus diameter on d 11 (r = 0.60, P < 0.01, for each day). In contrast, tRBP (r = 0.49, P < 0.01), tAP (r = 0.53, P < 0.01), and tFBP (r = 0.51, P < 0.01) in uterine flushings on d 11 were only correlated with d-3 plasma progesterone concentrations. No correlations between d-11 average conceptus diameter or d-11 uterine length with d-105 uterine capacity were observed. Uterine capacity was negatively correlated with placental weight, fetal weight and fetal hematocrit (r = -0.36, P < 0.01; r = -0.44, P < 0.01; r = -0.32, P < 0.01; respectively). Hematocrits were correlated with fetal plasma iron (r = 0.50, P < 0.01) and folates (r = 0.44, P < 0.01). Hematocrit, plasma iron, and plasma folate were each correlated with residual fetal weights after adjusting for placental weight (a measure of placental efficiency), and accounted for 11% of the variation in this trait. These data suggest that conceptus diameter and uterine protein secretion on d 11 may be influenced by the onset of progesterone secretion by the CL, but do not support an influence of conceptus growth during early pregnancy on uterine capacity. These results also suggest that reducing placental and fetal weights will likely result in increased uterine capacity.     

Transabdominal ultrasonographic determination of fetal gender in the horse during mid-gestation

Gender determination of the equine fetus using transabdominal ultrasonography was studied in 20 mares. One group of 10 research mares was scanned repeatedly every 2 weeks from 100 days gestation to parturition, while the second group of 10 client mares was subjected to echography once during mid-gestation. In males, the penis and/or prepuce was observed on 71 occasions from 102 days to 258 days gestation. On cross-sectional views, the male external genitalia had a round shape with parallel linear echogenic foci up to approximately 140 days gestation and then appeared triangular. Fetal testes were oval in shape in frontal view and had an homogeneous ultrasonographic appearance. Females were diagnosed on 23 occasions from 118 days to 227 days gestation based on the presence of the mammary glands and teats. Fetal ovaries appeared homogeneous with a characteristic circular echo from 100 days to 134 days gestation. Gender identifications (n = 98) based on the presence of the penis and/or prepuce in males and mammary glands and teats or fetal gonads in females were all correct, in agreement with the sex of the foals at birth. The optimal window of time was defined in both sexes as 100 to 220 days gestation. Thereafter, it was increasingly difficult to identify the anatomical structures cited above. Fetal sex was mainly determined using the transabdominal approach (87/98). However, the transrectal approach was useful in cases in which fetuses were either in posterior presentation or located very high in the mares abdomen. Good quality diagnostic scanners used typically in equine reproduction and equipped with a 5.0 MHz probe can be used for this procedure up to 160 days gestation, after which a 3.5 MHz transducer is often necessary due to increasing fetal size.     

Effect of number of conceptuses on maternal hormone concentrations in the pig

This study examined the effect of number of conceptuses on maternal concentrations and profiles of estrogen sulfate, estrone, estradiol-17 beta, progesterone and prolactin in gilts. Estradiol-valerate injections were used to induce pseudopregnancy (O conceptuses; n = 5) and oviduct ligation or no treatment were utilized to obtain pregnant gilts with 4 to 7 (n = 4), or 8 to 11 (n = 4) conceptuses, respectively. Blood samples were collected every 10 d from d 10 through 110 of pregnancy or pseudopregnancy. At 110 d after onset of estrus, all gilts were slaughtered and numbers and(or) weights of fetuses, corpora lutea, placentae and the empty uterus were determined. Concentrations of estrogen sulfate and estrone, but not progesterone or prolactin, were associated with fetal number, total fetal weight, total placental weight or empty uterine weight. In contrast, only progesterone was highly correlated with number of corpora lutea. Results suggest that most conjugated estrogen, estrone and estradiol were of fetal-placental origin, whereas little, if any, placental production of progesterone or prolactin occurred. Increases in estrogen sulfate and estrone concentrations were observed at gestation d 30 and from d 70 to 100. The latter increase coincides with previously established increases in the rate of maternal mammary development and fetal growth.     

Early fetal sexing of Saanen goats by use of transrectal ultrasonography to identify the genital tubercle and external genitalia

OBJECTIVE: To define the optimum period for sexing of Saanen goat fetuses by use of transrectal ultrasonography. ANIMALS: 82 Saanen goats pregnant with 124 fetuses. PROCEDURES: Fetal sexing was performed on the basis of the final location of the genital tubercle or identification of external genitalia. In experiment 1, fetuses (n = 78) were monitored every 48 hours from days 40 to 60 of gestation, whereas for experiment 2, 46 fetuses were examined only once between days 47 and 77 of gestation. RESULTS: For experiment 1, accuracy of fetal sexing was 20 of 20 (100%) for a single fetus, 39 of 42 (92.8%) for twin fetuses, and 10 of 16 (62.5%) for triplet fetuses. Diagnostic accuracy was significantly lower for triplet fetuses than that for single or twin fetuses. Final location of the genital tubercle was detected between 45 and 55 days of gestation (mean +/- SEM, 48.9 +/- 1.8 days). For experiment 2, accuracy of fetal sexing for a single fetus (24/24 [100%]) was significantly higher than the accuracy for twin fetuses (16/22 [72.7%]). Considering all fetuses that were born, accuracy of diagnosis was 69 of 78 (88.4%) for experiment 1 and 40 of 46 (86.9%) for experiment 2. Accuracy did not differ significantly between experiments. CONCLUSIONS AND CLINICAL RELEVANCE: Real-time ultrasonography after day 55 of gestation is a suitable method for determination of sex of Saanen goat fetuses by observation of the genital tubercle or identification of external genitalia.     

Relationships between uterine and fetal traits in rabbits selected on uterine capacity

The aim of this study was to investigate whether uterine capacity (UC) in rabbits was related to uterine horn length and weight and whether these uterine traits and vascular supply were related to fetal development and survival. Data from 48 unilaterally ovariectomized (ULO) does of the High and 52 ULO does of the Low UC lines of a divergent selection experiment on UC were used. Does were slaughtered on d 25 of fifth gestation. The High line showed higher ovarian weight (0.08 g, P < 0.05) linked to a higher ovulation rate (1 ovum, P < 0.05) and greater length of the empty uterine horn. There were no differences between lines in the remaining doe traits. The number of implanted embryos and live fetuses, fetal survival, and uterine weight and length were positively associated and explained most of the observed variation. Average weights of the live fetuses and their fetal and maternal placentae were not related to uterine weight and length. The linear regression coefficient of full uterine horn length on the number of live fetuses was 2.43 +/- 0.21. The weight of the full uterine horn showed a small quadratic relationship (P < 0.05) with the number of live fetuses. Full uterine horn length, after adjusting for the number of embryos, was negatively associated (P < 0.001) with the number of dead fetuses. The linear regression coefficient of average fetal placental weight of the live fetuses on number of implanted embryos was higher (P < 0.10) in the Low line (-0.23 +/- 0.04 vs. -0.12 +/- 0.04). The linear regression coefficient of average weight of the live fetuses on the average weight of their fetal placentae was higher (P < 0.10) in the High line (2.56 +/- 0.47 vs. 1.27 +/- 0.57). The High line was more efficient, most likely because an increase in intrauterine crowding has a lesser effect on the development of fetal placentae and fetuses. The fetal position within the uterus did not affect the proportion of dead embryos. Fetuses with placentae receiving a single blood vessel had a higher probability of death (P < 0.001) and the lowest weight. There was no difference between lines for individual weight of the live fetuses, but the High line showed higher individual weights of fetal (P < 0.01) and maternal placentae (P < 0.10). Live fetuses in the midportion of the uterus were lighter in weight (P < 0.05) than in the oviductal and cervical regions (20.3 vs. 21.6 and 21.7g). Increasing uterine capacity increases uterine length and decreases weights of fetus and fetal placenta in rabbits.