Number of fetuses and conceptus growth throughout gestation in lines of pigs selected for ovulation rate or uterine capacity

Selection for 11 generations in swine for ovulation rate (OR) or uterine capacity (UC) resulted in 19.6% greater prenatal survival at term in UC compared with OR. Our objective was to characterize the number of fetuses throughout gestation in each line, including an unselected control (CO) line. Five hundred ninety-three gilts produced over 4 farrowing seasons were subjected to unilateral-hysterectomy-ovariectomy at 160 d of age and mated within line at 280 d of age. Gilts were assigned within sire family to be slaughtered (+/- 2 d) at d 25, 45, 65, 85, or 105 of gestation. Ovulation rate and number of live and dead fetuses were recorded for each pregnant gilt (n = 402). Fetal and placental weights were also recorded. Ovulation rate of OR line gilts (18.0 +/- 0.3 ova) exceeded (P < 0.001) CO and UC lines (15.0 +/- 0.3 and 14.0 +/- 0.3 ova, respectively). Line and gestational age interacted to affect number of live fetuses (P < 0.001). Least squares means for CO were 10.1, 8.3, 7.2, 6.7, and 7.3 live fetuses for d 25, 45, 65, 85, and 105, respectively (average SE = 0.46 fetuses). Corresponding means for OR were 13.4, 8.3, 7.9, 6.5, and 6.7 live fetuses, respectively (average SE = 0.44 fetuses). Means for UC were 10.2, 9.0, 8.5, 7.5, and 8.0 live fetuses, respectively (average SE = 0.47 fetuses). In each line, number of live fetuses at d 25 was approximately 72% of ovulation rate. Mortality to d 45 was greatest in OR, intermediate in CO, and least in UC. Reductions in live fetuses continued to occur from d 45 to 105, but line differences at d 45 were essentially maintained to d 105. Number of live fetuses in gilts at d 114 was estimated from each of the survival curves and predicted values of 7.0, 5.9, and 7.8 per uterine horn for CO, OR, and UC lines, respectively. Selection for uterine capacity improved fetal survival primarily during the time period between d 25 and 45. Relative growth rate coefficients throughout gestation for placental tissue indicated a change in rank of the line means, implicating a relative later growth pattern of placental tissue in the UC line.     

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.     

Allelic variation in the secreted folate binding protein gene is associated with uterine capacity in swine

Previous comparisons between the cDNA and gene sequences for secreted folate binding protein (sFBP) indicated a 12-bp insertion/deletion (ins/del) polymorphism in exon 1 and a SNP that altered (Ser-Arg) the protein AA sequence. The effect of the Ser-Arg SNP on reproductive traits was examined in three groups of Meishan-White European breed crossbred gilts. The gilts for all three groups were unilaterally hysterectomized-ovariectomized (UHO) at 100 d of age. Group 1 gilts (n = 77) were mated at estrus, slaughtered at d 105 of pregnancy, and a blood sample was collected from each fetus to determine fetal hematocrit. The number of corpora lutea and fetuses and the fetal and placental weights were recorded. Group 2 gilts (n = 46) were mated, the remaining uterine horn was flushed with 20 mL of saline on d 11 of pregnancy, conceptuses were counted, and flushings were measured for total sFBP. Gilts were allowed an estrous cycle to recover, mated again at estrus, slaughtered at 105 d of gestation, and the data as described for Group 1 were collected. Groups 1 and 2 gilts were genotyped for the Ser-Arg SNP. In Group 3, gilts (n = 70) and boars (n = 30) were genotyped for the Ser-Arg SNP before mating, and like genotypes were mated. Gilts were then treated as described for Group 2. The effect of the 12-bp ins/del on reproductive traits was examined in 407 white crossbred UHO gilts from a randomly selected control line and from lines selected for ovulation rate (OR) and uterine capacity (UC). Gilts were mated and slaughtered at 105 d of age, and the numbers of corpora lutea and live fetuses, and fetal and placental weights and fetal hematocrits were recorded. The 12-bp ins/del also was evaluated in 131 intact gilts from the OR selected line. These gilts were mated at approximately 250 d of age and farrowed. The numbers of fully formed and live piglets were recorded. A significant effect (P < 0.05) of the Ser-Arg SNP was detected on the number of embryos present on d 11 of pregnancy and on UC. The sFBP 12-bp ins/del was associated with UC (P < 0.01) and the number of CL (P < 0.05) in UHO gilts, but not with litter size in intact gilts from the OR line. Results suggest that the 12-bp ins/del polymorphism could be exploited to increase litter size in swine, provided that the negative effect of the polymorphism on OR is overcome.     

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.     

Increased plasma follicle-stimulating hormone concentrations in prepubertal gilts from lines selected for increased number of corpora lutea

Plasma follicle-stimulating hormone (FSH) was evaluated in gilts from two studies in which ovulation rate was increased through direct selection for number of corpora lutea (CL) to determine whether selection for ovulation rate affected FSH secretion during prepubertal development. In the first study, 76 control and 110 selected gilts of University of Nebraska gene pool lines were bled twice during prepubertal development. Plasma FSH concentrations were greater (P < 0.05) at 53 (13.5%) and 75 (21.3%) d of age in selected than in control gilts. In the second study, 254 control gilts, 261 gilts from a line selected for ovulation rate, and 256 gilts from a line selected for uterine capacity were bled at three prepubertal ages. Plasma FSH was greater (P < 0.05), relative to controls, on d 34 (> 24%), 55 (> 13%), and 85 (> 10%) in White Composite gilts selected for either increased ovulation rate or for greater uterine capacity. Unilateral ovariectomy and hysterectomy were performed at 160 d of age on random gilts in these three lines (n = 377); weights of these organs were evaluated to determine whether selection affected their development. Ovarian and uterine weights were less (P < 0.01) in the control than in the ovulation rate line. Subsequently, ovulation rate was determined during pregnancy (n > or = 130 gilts/line). Controls had fewer (P < 0.01) CL (14.6) than gilts of the ovulation rate line (17.7) but numbers similar (P > 0.10) to those of gilts of the uterine capacity line (14.7). Within each line, plasma FSH only on d 85 correlated positively with subsequent ovulation rate (P < 0.03, 0.001, and 0.08; r = 0.17, 0.30, and 0.15 for control, ovulation rate, and uterine capacity lines, respectively). Ovarian weight at 160 d of age also correlated with subsequent ovulation rate (P < 0.03 and 0.001; r = 0.23 and 0.38) in control and ovulation rate gilts but not in uterine capacity gilts (P > 0.10; r = 0.11). Gilts selected for increased number of CL, in two independent studies, had greater concentrations of FSH during prepubertal development than respective controls. The modest but significant, positive association of FSH at 85 d of age with subsequent ovulation rate provides additional support for using plasma FSH in prepubertal gilts to indirectly select for ovulation rate.     

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.     

Response of nonpregnant versus pregnant gilts and their fetuses to severe feed restriction

Crossbred (Chester White X Landrace X Large White X Yorkshire) primiparous gilts were fed a standard gestation diet at 6,000 or 2,000 kcal calculated digestible energy (DE; 1.8 or .6 kg feed) daily for 84 or 108 (106 to 112) d after mating. Nonpregnant littermates were matched by body weight and assigned to the same diet treatments. Body weight and ultrasonic backfat measurements were made at 3-wk intervals. At 77 and 100 d, eight pregnant gilts (four control and four restricted) were fitted with indwelling jugular cannulas for frequent blood sampling (33 times over an 8-h period) to determine plasma glucose and growth hormone concentrations. At 84 and 108 d all gilts (eight pregnant and eight nonpregnant at d 84 and nine pregnant and nine nonpregnant at d 108 for each diet) were slaughtered and internal organs and reproductive tracts were removed and weighed. Fetal body and organ weights were recorded and an umbilical artery blood sample was removed from fetuses for plasma glucose, growth hormone, total protein and albumin measurements. The results demonstrated the ability of the primiparous gilt to maintain pregnancy through 106 to 112 d of gestation while consuming one-third (2,000 kcal DE daily) of recommended daily feed. Fetal weight at 84 and 108 d was reduced by about 13% without affecting litter size in gilts fed severely restricted intakes. Absolute and relative weights of maternal organs were affected by severe feed restriction, and backfat was reduced but there was no evidence of "pregnancy anabolism" in either adequately fed or restricted gilts. Fetal liver, kidney and gastrointestinal tract weights were reduced by maternal feed restriction; relative kidney weights were reduced while relative brain cortex weight was increased by maternal restriction. Maternal plasma glucose was unchanged by pregnancy or feed intake while plasma growth hormone peak amplitude, but not mean concentration or number of peaks, was increased by feed restriction. Fetal plasma glucose increased with time and in response to severe maternal feed restriction while plasma total protein and albumin decreased. Plasma growth hormone declined with time and was negatively correlated with fetal body weight.     

Changes in weight and composition in various tissues of pregnant gilts and their nutritional implications

The objectives of this study were to characterize the quantitative changes in various body tissues of high-lean type gilts during gestation and to determine the protein needs of pregnant gilts based on changes in tissue contents. Thirty-five gilts (158.2 +/- 8.3 kg) were housed in individual gestation crates with six unbred gilts randomly selected and slaughtered to provide data for d 0 of gestation. The remaining gilts were bred and assigned randomly to one of six slaughter groups: d 45, 60, 75, 90, 102, and 112. Gilts were fed 2 kg (as-fed basis) of gestation diet daily (3.1 Mcal/kg of ME and 0.56% lysine). Carcass soft tissue, bone, gastrointestinal tract, spleen, pancreas, kidney, liver, uterus, fetus, mammary gland, and the remaining viscera were separated and weighed. Carcass soft tissue, liver, remaining viscera, uterus, and gastrointestinal tract were ground, freeze-dried, and analyzed for composition. Body weights of the gilts increased quadratically (P < 0.001) during gestation. Weights of carcass soft tissue and uterus, including placenta, increased linearly (P < 0.001) during gestation. Weights of individual fetuses, fetal litters, individual mammary glands, and the entire mammary glands increased cubically (P < 0.001) during gestation. Crude protein in carcass soft tissue increased cubically (P < 0.01), whereas DM and ether extract (EE) in carcass soft tissue increased linearly (P < 0.01). The DM, CP, and EE in the entire mammary glands increased quadratically (P < 0.001) during gestation. The DM, CP, and EE in fetal litter increased cubically (P < 0.01) as gestation progressed. The accretion rates of the conceptus, fetal litter, individual fetus, individual mammary gland, and CP in fetal litter differed (P < 0.05) before and after d 70 of gestation. The CP daily gain from all maternal and fetal tissues was 40 and 103 g/d before and after d 70 of gestation, respectively, suggesting that pregnant gilts may require different quantities of dietary protein during gestation. Based on the maintenance requirement, maternal tissue gain, and conceptus gain, pregnant gilts require 6.8 and 15.3 g/d of true ileal-digestible lysine (or 147 and 330 g/d of true ileal-digestible protein) before and after d 70 of gestation, respectively, to support their true biological needs.     

Effect of estradiol-17beta administration during the time of conceptus elongation on placental size at term in Meishan pigs

Meishan embryos transferred to recipient females on d 2.5 are larger, contain greater numbers of trophectoderm cells, and secrete greater amounts of estradiol-17beta (E2beta) when gestated in a Yorkshire as compared with Meishan uterus to d 12. Additionally, placentas of Meishan conceptuses are larger when gestated in a Yorkshire as compared with Meishan uterus throughout gestation. Embryonic E2beta secretion during elongation on d 12 to 13 of gestation is temporally associated with endometrial secretion of growth factors, including IGF-I, which has been shown to increase mitotic rate in the trophectoderm of pig embryos. This experiment was conducted to determine whether E2beta administration to Meishan gilts at the time of conceptus elongation would increase placental size at term. Meishan gilts (n = 12) were checked twice daily for estrus (0700 and 1900), and each was bred to a Meishan boar at 0 and 24 h after the onset of estrus (d 0). Gilts were randomly assigned in equal numbers to receive injections of sesame oil (VEH) starting on d 12 (control), 1 mg of E2beta in VEH starting on d 12 (E212), or 1 mg of E2beta in VEH starting d 13 (E(2)13). The injections were initiated at 0700 or 1900 (corresponding to the time of day they first exhibited estrus) and continued at 6-h intervals for 48 h, resulting in 8 mg of E2beta given in eight injections. Pregnant gilts were killed on d 112 of gestation, and ovulation rate, litter size, implantation site length, fetal weight, crown-rump length, placental weight, and placental surface area were quantified. There were no differences among E(2)12, E(2)13, and control females in ovulation rate or litter size, which averaged 16.3 +/- .7 and 11.8 +/- .7, respectively. Fetal weight and crown-rump length were not different (P > .10) among E(2)12, E(2)13, and control females, averaging 802 +/- 26 g and 24.3 +/- .3 cm. Placentas were markedly heavier (176 +/- 14 and 174 +/- 16 vs 134 +/- 10 g, P < .05) and larger (1,337 +/- 97 and 1,520 +/- 70 vs 978 +/- 29 cm2, P < .001) for E(2)12 and E(2)13 vs control gilts, respectively. Placental efficiency (estimated as fetal weight:placental weight) was greater (P < .05) in the control than in the E(2)12 and E(2)13 gilts (5.8 +/- .2 vs 4.8 +/- .2 and 5.1 +/- .4). These data demonstrate that the amount of E2beta exposure around the time of elongation affects placental size at term. Additionally, the difference in placental efficiency between control and E2beta groups indicate that E2beta-induced increases in placental size led to a reduced placental efficiency.     

Justification of unilateral hysterectomy-ovariectomy as a model to evaluate uterine capacity in swine

Experimental objectives were to measure the effect of ovulation rate on litter size at 86 d of gestation and at farrowing in 110 unilaterally hysterectomized-ovariectomized (UHO) gilts and in 142 intact, control gilts and to evaluate postnatal survival and development of progeny. Surgery (UHO) was performed on gilts 8 to 12 d following first estrus. Control and UHO gilts were mated and then randomly assigned to be slaughtered at d 86 of gestation or allowed to farrow. Gilts scheduled to farrow were observed by laparoscopy on d 40 of gestation to count corpora lutea (CL). Ovulation rate (number of CL) was similar for control (12.1 CL) and UHO (11.9 CL) gilts, thus indicating that compensatory ovarian hypertrophy had occurred in UHO gilts and resulted in a near doubling of ova per uterine horn relative to control gilts. Average litter size at 86 d of gestation and farrowing was greater (P less than .01) for control than UHO gilts. At farrowing, litter size for control and UHO gilts was 9.0 +/- .3 and 5.7 +/- .3 pigs, respectively. Fetal losses were greater and pig weights at birth were less in litters by UHO gilts. Postnatal pig survival, growth rate to 14 d of age and 14-d individual pig weight did not differ for progeny of control and UHO gilts, and performance of UHO pogeny did not appear to compromise the usefulness of this animal model. Regression of litter size on ovulation rate was .41 +/- .15 pigs/CL for UHO and .60 +/- .12 pigs/CL for control gilts at d 86 of gestation. Regression was .07 +/- .17 pigs/CL for UHO and .42 +/- .14 pigs/CL for control gilts at farrowing.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Relationship of fetal position within the uterus to fetal weight, placental weight, testosterone, estrogens, and thymosin beta 4 concentrations at 70 and 104 days of gestation in swine.

Fetal intrauterine position relative to the sex of adjacent fetuses has an effect on reproductive performance in rodents. An experiment was conducted to determine whether sex of adjacent fetuses in utero has an influence on fetal and placental weights and whether the hormonal mechanisms documented in rodents are similar in fetal pigs. Sows were slaughtered at 70.1 +/- 1.7 d (n = 123) and 104.5 +/- .05 d (n = 135) of gestation. The fetuses and placentas were removed from the uterus and the position and sex of each fetus was recorded to indicate whether the fetus was between two males, two females, or a male and a female. Fetal blood was sampled for later hormonal analysis. At 70 d of gestation, male fetal and placental weights were heavier than those of females (P less than .05), but no differences were detected relative to the sex of adjacent fetuses. At 104 d of gestation, a fetus surrounded on each side in utero by fetuses of the opposite sex (two males or two females) was lighter in weight than a fetus surrounded by fetuses of the same sex (P less than .01). Differences in fetal weight due to the sex of adjacent fetuses were not related to placental function because placental weights were generally not different at 104 d of gestation. By 104 d of gestation, most placentas were not separated by necrotic regions and were in close apposition with surrounding placentas. No differences in growth or development could be related to hormonal effects (testosterone, estrone, or estrone sulfate) from surrounding fetuses.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Effects of exogenous somatotropin during early gestation on maternal performance, fetal growth, and compositional traits in pigs

The objective of this study was to determine the effects of maternal treatment with porcine somatotropin (pST) during early gestation on embryonic survival, fetal development, and internal environment for fetal growth. Sixty-two crossbred gilts received daily injections of either 3 mL of a placebo (control, n = 31) or 6 mg of pST (n = 31) from d 10 to 27 of gestation. Representative gilts were slaughtered on d 28, 37, and 62 of gestation. The remaining gilts were allowed to farrow. It was found that embryonic survival was not influenced by pST treatment (P > 0.10). However, pST affected the growth and composition of the maternal (endometrium) and fetal (chorion) parts of the placenta. Thus, endometrial RNA concentration tended to be increased by pST at d 37 (P = 0.15), and it was increased at d 62 (P < 0.05) of gestation, which is indicative of increased capacity for protein synthesis. At birth, placental chorion weight (P < 0.10) and contents of DM and protein (P < 0.05) were increased due to pST treatment, but no effects were detectable up to d 62 of gestation. Maternal pST treatment was effective at increasing nutrient supply to the embryo as suggested from elevated glucose concentrations in amniotic and allantoic fluids (P < 0.05) at d 28 of gestation. With regard to prenatal growth, embryonic DNA concentration was slightly elevated at d 28 (P < 0.10), but pST did not induce any changes in average embryonic, fetal, or neonatal weights. However, within litters, the birth weights of piglets in the 25% lowest weight group (LW) were increased by pST treatment vs control LW pigs (1,241+/-55 vs 1,099+/-59 g, P < 0.10). Thirty-eight neonates from 15 litters divided among the three weight groups were examined for body composition. The weight of the intestinal tract was increased above average after maternal pST treatment (P < 0.01). Additionally, the amounts of tissues such as bone (P = 0.12) and s.c. fat (P = 0.06), and of protein, fat (P = 0.10), and ash (P < 0.05) were increased, whereas the relative body composition remained unchanged by pST (P > 0.10). On average, muscle protein concentration was elevated due to pST (P < 0.01), and, in LW piglets, plasma IGF-I concentration was increased (P < 0.10). The results suggest that maternal somatotropin is a critical factor in early pregnancy capable of influencing placental nutrient transfer and placental growth. It thereby selectively improves the growth conditions for the smaller littermates.     

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.     

Mass selection for increased 70-day weight in a closed line of Landrace pigs

Mass selection for increased weight at 70 d of age was practiced for six generations in a line of Landrace pigs. It was desired to have the next generation sired by the heaviest nine boars and out of the heaviest 27 gilts. A contemporaneous, randomly selected (by pedigree) control line was maintained in which the next generation was sired by five boars and out of 10 gilts. Inbreeding coefficients were .208 and .214 for the selected and control line litters and .177 and .189 for the selected and control line dams in the sixth generation, respectively. A total of 1,906 pigs was farrowed with 70-d weights collected on 1,267 pigs. These pigs were sired by 88 boars and out of 190 gilts. The generation interval was 13 mo. Six traits were studied: birth, 21-d, 35-d and 70-d weights and preweaning (from birth to 35 d) and postweaning (from 35 to 70 d) daily gains. Direct and correlated responses per generation and per weighted cumulative selection differential (WCSD) were estimated. Total WCSD for 70-d weight was 30.3 kg. This corresponds to a standardized WCSD of 6.11 phenotypic standard deviations. The response per generation for 70-d weight was .65 +/- .29 kg. The realized heritability for 70-d weight was .13 +/- .06. Nearly all the increased weight at 70 d was the result of more rapid growth in the postweaning period, with little difference in growth in the preweaning period; birth, 21-d and 35-d weights and preweaning daily gains remained unchanged by selection for 70-d weight.     

Role of uteroferrin in placental iron transport in swine: relationship between uteroferrin levels and iron deposition in the conceptus during gestation

This study was to examine the relationship between uteroferrin and Fe, and Fe and Cu in the fetal pig. In Exp. 1, conceptus tissues and fluids were obtained on d 30, 45, 60, 75 and 90 of gestation for Fe and Cu analyses. In fetus minus liver, total Fe and Cu increased constantly between d 30 and 90, but Fe and Cu concentrations (microgram/g dry tissue) both decreased between d 30 and 45 and then remained relatively constant to d 90. For fetal liver, total Fe increased from d 30 (27 micrograms) to d 90 (3,222 micrograms), as did total Cu (14 micrograms on d 30 to 960 micrograms on d 90). Fetal liver Fe concentration (microgram/g dry tissue) decreased from d 30 (1,021) to d 60 (472) and then increased to d 90 (1,082), whereas Cu concentration increased between d 30 (537) and 60 (830) and then decreased between d 60 (471) and 90 (329). In allantoic fluid, both total Fe and Cu increased between d 30 and 60 and then decreased to d 90. Data from this study indicated a close temporal relationship between Fe and Cu in the fetal tissues and fluids examined. In Exp. 2, the relationship between Fe and uteroferrin in fetal tissues and fluids was studied. Uteroferrin, measured indirectly by acid phosphatase activity and Fe in fetal tissues and fluid underwent closely related temporal changes between d 30 and 112 of gestation. Changes in total Fe and Fe concentration during gestation were similar to those described for Exp. 1 in fetus minus liver, fetal liver and allantoic fluid. In addition, total Fe and Fe concentration in placental and endometrial tissues were analyzed. It was concluded that uteroferrin provides a major source of Fe in endometrial secretion and that it may be stored in placental and endometrial tissues. The relationship between Fe and Cu in conceptus tissues and erythropoiesis also is discussed.     

Effect of selenium intake and fetal age on mRNA levels of two selenoproteins in porcine fetal and maternal liver

The objective of this study was to determine if levels of mRNA encoding cytosolic glutathione peroxidase (cGPx) and thioredoxin reductase (TrxR-1) change during fetal development, and if maternal Se intake during gestation affects the mRNA levels of these proteins. Prepubertal gilts (n = 24) were randomly assigned to either Se-adequate (0.39 ppm of Se; n = 12) or Se-deficient (0.05 ppm of Se; n = 12) diets, 6 wk before breeding. Maternal liver was collected at d 10, 45, 70, and 114 of pregnancy, and fetal liver samples were collected at the same times except d 10. Complementary DNA sequences encoding cGPx and TrxR-1 were cloned and sequenced. Quantitative real-time PCR analysis indicated that levels of mRNA for cGPx in fetal liver decreased more than 3-fold between d 45 and 114 of gestation. Although the gilts were only marginally deficient in Se, and maternal Se intake did not affect cGPx mRNA levels in fetal liver, the low-Se diet tended (P = 0.1) to reduce fetal TrxR-1 mRNA levels. In the liver of the dams, the low Se intake did not affect mRNA levels for either cGPx or TrxR-1. Compared with the liver of the dams, mRNA levels for cGPx were about 3.5 times lower in fetal liver. Results of this study support the hypothesis that neonatal pigs are born with reduced cGPx corresponding to reduced cGPx mRNA levels during late gestation.     

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.