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.     

Genetic implications of a simulation model of litter size in swine based on ovulation rate, potential embryonic viability and uterine capacity: II. Simulated selection

Direct selection for ovulation rate, uterine capacity, litter size and embryo survival and selection for indexes of ovulation rate with each of the remaining traits were simulated for a swine population. The relationships among these traits were determined from a simulation model that assumed that litter size was always less than or equal to both ovulation rate and uterine capacity. Heritabilities of ovulation rate and uterine capacity were assumed to be .25 and .20, respectively, and uncorrelated genetically and phenotypically. No additional genetic variation was assumed. Responses to weak selection pressure were simulated by recurrent updating of phenotypic variances and covariances combined with the heritabilities of ovulation rate and uterine capacity. Two indexes of ovulation rate and uterine capacity each resulted in 37% greater increase in litter size than direct selection for litter size. Indexes of ovulation rate and either litter size or embryo survival increased litter size by 21% more than direct selection for litter size. Selection for ovulation rate, uterine capacity or embryo survival was 6, 35 and 79%, respectively, less effective than direct selection for litter size. Responses to intense selection pressure were determined by direct simulation of genotypes and phenotypes of individuals. The two indexes of ovulation rate and uterine capacity exceeded direct selection for litter size by 39 and 27%. The indexes of ovulation rate and either litter size or embryo survival exceeded direct selection for litter size by 19 and 13%, respectively. Intense selection for ovulation rate or uterine capacity decreased selection response by 26 and 67%, respectively, relative to direct selection for litter size. Intense selection for embryo survival decreased litter size slightly.     

Boar sperm quality in lines of pigs selected for either ovulation rate or uterine capacity

Selection for 11 generations in swine for ovulation rate (OR) or uterine capacity (UC) resulted in significant changes in component traits of litter size. Our objective was to conserve the unique germplasm for the future and to characterize sperm quality as a correlated response to the selection criterion imposed compared with an unselected control line (CO). Boars representing genetic diversity available in all 3 lines were produced in 2 farrowing seasons. Season 1 was born in September 2005 and was sampled for semen characteristics in October 2006. Season 2 was born in March 2006 and was sampled for semen characteristics in February and March 2007. Each boar (n = 60) was collected twice. The sperm-rich fraction was obtained, and volume and concentration of sperm cells were measured to estimate total sperm production. Each ejaculate was extended 1:3 (vol/vol) with Androhep Plus (Minitube, Verona, WI) and was packed for shipping to the National Animal Germplasm Program laboratory for processing into frozen straws. Semen quality was measured by computer-assisted semen analysis at 3 semen processing points: fresh (FR), 24 h after extender added (E), and postthaw (PT). A mixed model ANOVA was applied to the data. Fixed effects of farrowing season, line, and 2-way interactions were fitted. The random effect of boar (n = 60) within farrowing season and line was used to test line differences. Sperm concentration was not different (P = 0.18) among the lines (0.594 × 10(9), 0.691 × 10(9), and 0.676 × 10(9) cells/mL for CO, OR, and UC lines, respectively). However, significance (P = 0.04) was detected for the volume of the sperm-rich fraction, greatest for OR (86.4 mL), intermediate for UC (75.5 mL), and least for CO (70.2 mL). Line differences were thus detected (P = 0.02) for total sperm production per ejaculate, greatest for OR (54.9 × 10(9)), intermediate for UC (48.7 × 10(9)), and least for CO (40.5 × 10(9)). A larger percentage of progressively motile sperm and greater estimates of sperm velocity only at processing point E (P < 0.01) were detected in favor of CO. Estimates of motility, velocity, and other parameters of sperm movement measured on E processing points were positively correlated with the same estimates obtained PT, but the magnitude was low to moderate (r range -0.03 to 0.23). Thus, selection for component traits of female reproduction had a favorable effect on total sperm production of boars.     

Direct responses to selection for increased litter size, decreased age at puberty, or random selection following selection for ovulation rate in swine

Nine generations of selection for high ovulation rate were followed by two generations of random selection and then eight generations of selection for increased litter size at birth, decreased age at puberty, or continued random selection in the high ovulation rate line. A control line was maintained with random selection. Line means were regressed on generation number and on cumulative selection differentials to estimate responses to selection and realized heritabilities. Genetic parameters also were estimated by mixed-model procedures, and genetic trends were estimated with an animal model. Response to selection for ovulation rate was about 3.7 eggs. Response in litter size to selection for ovulation rate was .089 +/- .058 pigs per generation. Average differences between the high ovulation rate and control lines over generations 10 to 20 were 2.86 corpora lutea and .74 pigs (P less than .05). The regression estimate of total response to selection for litter size was 1.06 pigs per litter (P less than .01), and the realized heritability was .15 +/- .05. When the animal model was used, the estimate of response was .48 pigs per litter. Total response in litter size to selection for ovulation rate and then litter size was estimated to be 1.8 and 1.4 pigs by the two methods. Total response to selection for decreased age at puberty was estimated to be -15.7 d (P less than .01) when data were analyzed by regression (realized heritability of .25 +/- .05) and -17.1 d using the animal model. No changes in litter size occurred in the line selected for decreased age at puberty. Analyses by regression methods and mixed-model procedures gave similar estimates of responses and very similar estimates of heritabilities.     

Direct and correlated responses to two-stage selection for ovulation rate and number of fully formed pigs at birth in swine

Our objectives were to estimate responses and genetic parameters for ovulation rate, number of fully formed pigs at birth, and other production traits following two-stage selection for increased ovulation rate and number of fully formed pigs. Eight generations of selection were practiced in each of two lines. One selection line was derived from a line that previously selected eight generations for an index to increase ovulation rate and embryonic survival (the IOL pigs). The other selection line was derived from the unselected control line of the index selection experiment (the COL pigs). The control line (C) was continued with random selection. Due to previous selection, Line IOL had greater ovulation rate (4.24 +/- 0.38 and 4.14 +/- 0.29 ova) and litter size (1.97 +/- 0.39 and 1.06 +/- 0.38 pigs) at Generation 0 of two-stage selection than did Lines COL and C. In Stage 1, all gilts from 50% of the largest litters were retained. Approximately 50% of them were selected for ovulation rate in Stage 2. Gilts selected for ovulation rate were mated to boars selected from the upper one-third of the litters for litter size. At Generations 7 and 8, differences in mean EBV for ovulation rate and litter size between Lines IOL and C were 6.20 +/- 0.29 ova and 4.66 +/- 0.38 pigs; differences between Lines COL and C were 2.26 +/- 0.29 ova and 2.79 +/- 0.39 pigs; and differences between Lines IOL and COL were 3.94 +/- 0.26 ova and 1.86 +/- 0.39 pigs. Regressions of line mean EBV on generation number were 0.27 +/- 0.07 ova and 0.35 +/- 0.06 pigs in Line IOL; 0.30 +/- 0.06 ova and 0.29 +/- 0.05 pigs in Line COL; and 0.01 +/- 0.07 ova and 0.02 +/- 0.05 pigs in Line C. Correlated responses were decreased age at puberty and increased number of pigs born alive, number of mummified pigs, prenatal loss, and individual and litter birth weight. Two-stage selection for ovulation rate and number of pigs per litter is a promising procedure to improve litter size in swine.     

Candidate gene analysis for loci affecting litter size and ovulation rate in swine

A candidate gene approach was used to determine whether specific loci explain responses in ovulation rate (OR) and number of fully formed (FF), live (NBA), stillborn, and mummified pigs at birth observed in two lines selected for ovulation rate and litter size compared with a randomly selected control line. Line IOL was selected for an index of OR and embryonic survival for eight generations, followed by eight generations of two-stage selection for OR and litter size. Line C was selected at random for 16 generations. Line COL, derived from line C at Generation 8, underwent eight generations of two-stage selection. Lines IOL and C differed in mean EBV by 6.1 ova and 4.7 FF, whereas lines COL and C differed by 2.2 ova and 2.9 FF. Pigs of Generation 7 of two-stage selection lines were genotyped for the retinol binding protein 4 (RBP4, n = 190) and epidermal growth factor (EGF, n = 189) loci, whereas pigs of Generations 7 and 8 were genotyped for the estrogen receptor (ESR, n = 523), prolactin receptor (PRLR, n = 524), follicle-stimulating hormone beta (FSHbeta, n = 520), and prostaglandin-endoperoxide synthase 2 (PTGS2, n = 523) loci. Based on chi-square analysis for homogeneity of genotypic frequencies, distributions for PRLR, FSHbeta, and PTGS2 were different among lines (P < 0.005). Differences in gene frequencies between IOL vs C and COL vs C were 0.33 +/- 0.25 and 0.16 +/- 0.26 for PRLR, 0.35 +/- 0.20 and 0.15 +/- 0.24 for FSHbeta, and 0.16 +/- 0.16 and 0.08 +/- 0.18 for PTGS2. Although these differences are consistent with a model of selection acting on these loci, estimates of additive and dominance effects at these loci did not differ from zero (P > 0.05), and several of them had signs inconsistent with the changes in allele frequencies. We were not able to find significant associations between the polymorphic markers and phenotypes studied; however, we cannot rule out that other genetic variation within these candidate genes has an effect on the traits studied.     

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.     

Responses in ovulation rate, embryonal survival, and litter traits in swine to 14 generations of selection to increase litter size

Eleven generations of selection for increased index of ovulation rate and embryonal survival rate, followed by three generations of selection for litter size, were practiced. Laparotomy was used to count corpora lutea and fetuses at 50 d of gestation. High-indexing gilts, approximately 30%, were farrowed. Sons of dams in the upper 10% of the distribution were selected. Selection from Generations 12 to 14 was for increased number of fully formed pigs; replacements were from the largest 25% of the litters. A randomly selected control line was maintained. Responses at Generation 11 were approximately 7.4 ova and 3.8 fetuses at 50 d of gestation (P < .01) and 2.3 fully formed pigs (P < .01) and 1.1 live pigs at birth (P < .05). Responses at Generation 14 were three fully formed pigs (P < .01) and 1.4 live pigs (P < .05) per litter. Number of pigs weaned declined (P < .05) in the index line. Total litter weight weaned did not change significantly. Ovulation rate and number of fetuses had positive genetic correlations with number of stillborn pigs per litter. Significantly greater rate of inbreeding and increased litter size at 50 d of gestation in the select line may have contributed to greater fetal losses in late gestation, greater number of stillborn pigs, and lighter pigs at birth, leading to lower preweaning viability. Heritabilities of traits were between 8 and 25%. Genetic improvement programs should emphasize live-born pigs and perhaps weight of live-born pigs because of undesirable genetic relationships of ovulation rate and number of fetuses with numbers of stillborn and mummified pigs and because birth weight decreased as litter size increased.     

Effects of ovulation rate and fetal number on fertility in twin-producing cattle

Effects of ovulation rate and of fetal number and distribution within the uterus on pregnancy rate and fetal survival were evaluated in nulliparous (n = 1,331) and parous (n = 3,517) cattle selected for twinning. Cattle were divided into a spring (70 d) and fall (60 d) breeding season and bred by a combination of AI and natural service. Ovulation rate, pregnancy status, and fetal number and distribution were determined by transrectal, real-time ultrasonography of the uterus and both ovaries at the end of the breeding season. Pregnancy was reconfirmed by rectal palpation at 75 to 135 d of gestation. For heifers and cows combined, ovulation rate increased (P < 0.01) from 1.46 +/- 0.4 in 1994 to 1.89 +/- 0.4 in 2004; number of calves per parturition increased (P < 0.01) from 1.34 +/- 0.3 to 1.56 +/- 0.3, respectively, which included an increase in triplet and quadruplet ovulations and triplet births. Bilateral twin ovulations yielded proportionately more (P < 0.01) twin births than unilateral twin ovulations. Ovulation rate was greater (P < 0.01) in the fall than spring breeding season. Pregnancy rate at ultrasound diagnosis did not differ among females with 1, 2, or 3 ovulations (89.1 +/- 0.7, 91.2 +/- 0.7, or 91.5 +/- 2.8%, respectively), but rates at calving decreased (P < 0.01) with increasing ovulation rate (85.1 +/- 0.6, 82.7 +/- 0.6, or 64.2 +/- 2.7%, respectively). Pregnancy rate was less (P < 0.01) after twin or triplet births than single births. For dams birthing twins or triplets, pregnancy rate was less in the fall vs. spring, but rates were similar between seasons for dams with a single birth (type of birth x season, P < 0.05). Cows 60 d, regardless of type of birth. Maintenance of pregnancy to term differed (P < 0.01) among females diagnosed with 1, 2, or 3 fetuses (95.7 +/- 0.6, 87.8 +/- 0.8, and 54.9 +/- 2.3%, respectively). The reduced survival of twin and triplet fetuses in heifers had occurred (P < 0.01) by d 75 to 135 of gestation, and fetal losses were greater (P < 0.01) for unilateral than bilateral twins or triplets, whereas loss of twin or triplet fetuses in cows occurred later in gestation, and losses were not affected by uterine location. Thus, increased calf production from selecting for increased ovulation rate in beef cattle is tempered by increased fetal mortality, partially associated with the crowding of 2 or 3 fetuses within 1 uterine horn, especially in heifers.     

A Bayesian analysis of response to selection for uterine capacity in rabbits

A divergent, eight generation selection experiment on uterine capacity in rabbits was performed. Rabbit does were ovariectomized unilaterally before puberty, and selected for increased and decreased litter size by 'best linear unbiased prediction' using data from up to four parities. Two different analyses were performed to estimate the response to selection. The first was based on least squares analysis; the second was based on Bayesian methods using Gibbs sampling techniques. Three different priors were used for variance components, but these had little influence on the results. Posterior means of heritabilities for uterine capacity, varied from 0.09 to 0.12, and repeatabilities from 0.18 to 0.22. The response to eight generations of selection was symmetrical and led to a divergence of 0.16 young rabbits per generation, which amounts to about 2% of the average litter size of the base population per generation. The pattern of response however, was not linear: a high initial response was followed by a period where little further response was observed, and a final burst of response was obtained during the last two cycles of selection.     

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.     

Effect of selection for litter size and body weight on hormone-induced ovulation rate in mice.

Genetic differences in natural vs hormone-induced ovulation rates were compared in immature female mice from five lines that had undergone long-term single-trait and antagonistic index selection for litter size and(or) 6-wk BW. Lines used were control (K); high litter size (L+); high BW (W+); low litter size and high BW (L-W+); and high litter size and low BW (L+W-). Natural ovulation rate at a mean age of 34.3 d and hormone-induced (5 IU of pregnant mare's serum gonadotropin followed 2 d later by 5 IU of human chorionic gonadotropin) superovulation rate at a fixed age of 31 d were obtained. Total number of eggs ovulated was affected by line (P less than .001), treatment (P less than .001), and line x treatment interaction (P less than .001). Line differences were subsequently tested within treatment because of the significant line x treatment interaction. Line differences were important (P less than .001) for natural ovulation, hormone-induced ovulation, and response to hormones. Mean natural ovulation rates for K, L+, W+, L-W+, and L+W- were 14.1, 19.8, 15.1, 13.6, and 16.4, respectively. Selection changed ovulation rate by 40, 16, 7, and -4% in the L+, L+W-, W+ and L-W+ lines, respectively (P less than .01). Hormone-induced ovulation rates in K, L+, W+, L-W+, and L+W- were 32.3, 24.6, 19.6, 20.9, and 22.1, respectively. Exogenous hormones increased ovulation by 18.2, 4.8, 4.6, 7.3, and 5.7 ova for K, L+, W+, L-W+, and L+W-, respectively (P less than .001). Lines with lower natural ovulation rates had higher responses to superovulation. Increased ovulation rate due to treatment ranged from 24.3% in L+ to 129% in K. These results indicate significant differences among lines in ovarian response to exogenous hormones.     

Fine mapping a quantitative trait locus affecting ovulation rate in swine on chromosome 8

Ovulation rate is an integral component of litter size in swine, but is difficult to directly select for in commercial swine production. Because a QTL has been detected for ovulation rate at the terminal end of chromosome 8p, genetic markers for this QTL would enable direct selection for ovulation rate in both males and females. Eleven genes from human chromosome 4p16-p15, as well as one physiological candidate gene, were genetically mapped in the pig. Large insert swine genomic libraries were screened, clones were isolated and then screened for microsatellite repeats, and informative microsatellite markers were developed for seven genes (GNRHR, IDUA, MAN2B2, MSX1, PDE6B, PPP2R2C, and RGS12). Three genes (LRPAP1, GPRK2L, and FLJ20425) were mapped using genotyping assays developed from single nucleotide polymorphisms. Two genes were assigned since they were present in clones that contained mapped markers (HGFAC and HMX1). The resulting linkage map of pig chromosome 8 contains markers associated with 14 genes in the first 27 cM. One inversion spanning at least 3 Mb in the human genome was detected; all other differences could be explained by resolution of mapping techniques used. Fourteen of the most informative microsatellite markers in the first 27 cM of the map were genotyped across the entire MARC swine resource population, increasing the number of markers typed from 2 to 14 and more than doubling the number ofgenotyped animals with ovulation rate data (295 to 600). Results from the revised data set for the QTL analysis, assuming breed specific QTL alleles, indicated that the most likely position of the QTL resided at 4.85 cM on the new linkage map (F1,592 = 20.5150, genome-wide probability less than 0.015). The updated estimate of the effect of an allele substitution was -1.65 ova for the Meishan allele. The F-ratio peak was closest to markers for MAN2B2 (4.80 cM) and was flanked on the other side by markers for PPP2R2C. Two positional candidate genes included in this study are MAN2B2 and RGS12. These results validate the presence of a QTL affecting ovulation rate on chromosome 8 and facilitate selection of positional candidate genes to be evaluated.     

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 breed and intrauterine crowding on fetal erythropoiesis on day 35 of gestation in swine

In a previous report, it was suggested that intrauterine crowding impaired fetal erythropoiesis and that fetal erythropoiesis was accelerated in Meishan pigs during early pregnancy. Because these conclusions were based on limited numbers of observations, the present experiment was undertaken to provide a more extensive investigation of these phenomena. Intact white crossbred gilts, unilaterally hysterectomized-ovariectomized (UHO) white crossbred gilts, and intact Meishan gilts (n = 13 to 16 per group) were mated after at least one estrous cycle of normal duration (17 to 23 d). Gilts were laparotomized at d 35 of pregnancy, the uterine horns were exteriorized and opened near each fetus, and a blood sample was collected from each fetus. The uterine horn was then surgically removed, and each fetus and placenta was weighed. All fetal blood samples were measured for hematocrit, red blood cell number, and hemoglobin. Erythropoietin and the percentages of nucleated cells and reticulocytes were also measured in blood samples from the largest and smallest living fetus in each litter. Fetal hematocrits were not affected by treatment. Blood cell counts were greater (P < 0.01) in fetuses of Meishan gilts than in White crossbred intact or UHO gilts. Hemoglobin was less (P < 0.01) in fetuses of Meishan gilts than in fetuses of White crossbred intact or UHO gilts. The percentages of nucleated (immature) cells and reticulocytes were both less (P < 0.01) in fetuses of Meishan intact gilts. Erythropoietin was also lower (P < 0.01) in fetuses of Meishan gilts. As observed previously, fetal weight was correlated (r = 0.38; P < 0.01) with blood hemoglobin concentration. These results confirm that fetal erythropoiesis in Meishan gilts is accelerated compared with White crossbred gilts. These results are consistent with the hypothesis that faster blood cell development could be beneficial to fetal survival in swine.     

Doppler evaluation of maternal and fetal vessels during normal gestation in the bitch

The aim of this work is to evaluate the haemodynamic characteristics of maternal and fetal vessels during normal pregnancy in bitches, using Colour and Pulsed wave Doppler ultrasonography, in order to obtain more information about maternal and fetal circulation. The blood waveforms of the uteroplacental arteries, aorta, caudal cava vein and umbilical cord of the fetuses were recorded weekly in 16 pregnant bitches. Also, the measurements of Peak Systolic, End Diastolic Velocities, Resistance and Pulsatility Indices were carried out. Uteroplacental blood flow was biphasic while the ones of the umbilical artery and aorta were first systolic and then diastolic. The cava showed a typical waveform of venous vessels. During gestation the EDV and PSV of fetal vessels increased (alpha<0.05) while the PI and RI of all vessels examined decreased (alpha<0.05) except for the IP of the Aorta. The Doppler ultrasonography was used to study the characteristics of maternal and fetal vessel flow and their progressive changes during pregnancy. This study can be considered a further contribution in diagnosing and monitoring high-risk pregnancies in Veterinary Medicine.     

Direct responses to six generations of selection for ovulation rate or prenatal survival in Large White pigs

Effects of selection for ovulation rate or prenatal survival were examined using data from 3 pigs lines derived from the same base Large White population. Two lines were selected for 6 generations on high ovulation rate at puberty (OR line) or high prenatal survival corrected for ovulation rate in the first 2 parities (PS line). The third line was an unselected control line. Genetic parameters for ovulation rate on the left, right, and both ovaries at puberty (ORPL, ORPR, and ORP, respectively) and at fertilization (ORFL, ORFR, and ORF, respectively), total number of piglets born (TNB) per litter, prenatal survival (PS = TNB/ORF), and PS corrected for ovulation rate (CPS = PS + 0.018ORF) were estimated using REML methodology. Responses to selection were estimated by computing differences between OR or PS and control lines at each generation using least squares and mixed models methodology. Average genetic trends were computed by regressing line differences on generation number. Realized heritabilities were estimated using standard procedures. Heritability estimates were 0.17, 0.11, 0.34, 0.13, 0.09, 0.33, 0.14, 0.11, and 0.17 (SE = 0.01 to 0.03) for ORPL, ORPR, ORP, ORFL, ORFR, ORF, PS, CPS, and TNB, respectively. Realized heritabilities were 0.37 +/- 0.08 and 0.10 +/- 0.09 for ORP and CPS, respectively. The different measures of ovulation rate had strong genetic correlations (r(g) > 0.7). The ORF had midrange negative genetic correlations with PS and CPS (-0.45 +/- 0.07 and -0.42 +/- 0.08, respectively). The ORP also had an antagonistic genetic relationship with PS (-0.26 +/- 0.07) but was almost independent from CPS (-0.02 +/- 0.11). The TNB was moderately correlated with ORP and ORF (r(g) = 0.41 +/- 0.09 for both traits). Average genetic trends in OR and PS lines were, respectively, 0.49 +/- 0.10 and 0.11 +/- 0.10 for ORP, and 0.43 +/- 0.11 and 0.11 +/- 0.11 for ORF. Responses to selection were slightly superior in the left than in the right ovary. No significant difference was found for PS or CPS in any of the lines. The TNB did not change in the OR line but significantly improved in the PS line (0.24 +/- 0.11 piglets/generation).     

Immunolocalization of steroidogenic enzymes in equine fetal adrenal glands during mid-late gestation

To elucidate the relationship between steroidogenic hormones and developing adrenal glands, we investigated the immunolocalization of steroidogenic enzymes in equine fetal adrenal glands during mid-late gestation. Fetal adrenal glands were obtained from three horses at 217, 225 and 235 days of gestation. Steroidogenic enzymes were immunolocalized using polyclonal antisera raised against bovine adrenal cholesterol side-chain cleavage cytochrome P450 (P450scc), human placental 3beta-hydroxysteroid dehydrogenase (3betaHSD), porcine testicular 17alpha-hydroxylase cytochrome P450 (P450c17) and human placental aromatase cytochrome P450 (P450arom). Histologically, cortex and medulla cells were clearly observed in the three fetal adrenal gland tissue samples. P450scc and P450c17 were identified in cortex cells close to medulla cells and in some medulla cells in the fetal adrenal glands. P450arom was present in both cortex and medulla cells in the fetal adrenal glands. However, 3betaHSD was not found in any of the equine fetal adrenal gland tissue samples. These results suggest that equine fetal adrenal glands have the ability to synthesize androgen and estrogen, which may play an important physiological role in the development of equine fetal adrenal glands.