The effect of divergent selection for uterine capacity on prenatal survival in rabbits: maternal and embryonic genetic effects

The aim of this work was to determine whether prenatal survival depends on the genotype of the mother or of the embryo and to identify the critical periods for prenatal mortality in two lines of rabbits divergently selected by high (H) and low (L) uterine capacity. Does from H (n = 124) and L (n = 115) lines were slaughtered at 72 h of gestation. Embryos recovered at 72 h of gestation were transferred to the oviducts of recipient does from the H (n = 23) and L (n = 19) lines. Each recipient does received eight embryos from the H line into one oviduct and eight embryos from the L line into the other. Recipient does were slaughtered on d 28 of gestation. No differences were found between lines in the embryo recovery either in ovulation rate (OR) or in fertilization rate of ova recovered. Recovery rate was higher for the H line (0.80 vs. 0.72, P < 0.01). The number of embryos recovered, fitting ovulation rate as a covariate, was also higher for the H line (9.74 vs. 8.78, P < 0.05). The H line showed a more advanced embryonic stage of development, having a higher percentage of blastocysts (PB) and a lower percentage of compact morulae (PCM) (38% vs. 20%, P < 0.001 for PB, and 51% vs. 64%, P < 0.01 for PCM). The percentage of early morulae was low and similar in both lines. Neither donor nor recipient lines affected embryonic survival from 72 h to 7 d of gestation. Fetal survival was affected by the recipient line (P < 0.05). An interaction between donor and recipient was found. Embryos from the H donor line had a better fetal survival rate than embryos from the L donor line (P < 0.05) in H recipient females. Within L recipient females, embryos from H and L donor lines showed similar fetal survival. Fetal survival was divided into early (from d 7 to 17 of gestation) and late (from d 17 to 28 of gestation). The high recipient line showed a higher early fetal survival than the L recipient line (P < 0.05). The same effect was observed for late fetal survival, but the difference between H and L recipient lines was lower (P < 0.10). Thus, fetal survival depends mainly on the maternal genotype, and the embryo genotype only affects fetal survival when embryo transfer is performed to a favorable maternal environment. Selection for uterine capacity in rabbits leads to modification of early embryonic survival and of early and late fetal survival, but differences are higher for early than for late fetal survival.     

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.     

Effect of Embryonic and Maternal Genotype on Embryo and Foetal Survival in Rabbit

The aim of this work was to study the influence of embryonic and maternal genotype of two lines of rabbits selected by growth rate (line R) and litter size at weaning (line A) on prenatal survival. Embryos were recovered at 48 h of gestation from R and A donors (39 and 35 does, respectively) and reciprocally transferred to the oviducts of recipient does to the R (n = 15) and A (n = 14) lines. Each recipient doe received six embryos from line R into one oviduct and six embryos from line A into the other. Recipient does were examined by laparoscopy to determine implantation rate on day 14 and slaughtered on day 25 of gestation to determine the number of live foetuses and the weight of foetuses and placentas. No differences were found between lines in fertilization rate and stage of embryo development at 48 h post‐insemination. Implantation rate was affected by both the embryonic and maternal genotype. While embryos from donor line A had the highest implantation rate (0.78 ± 0.032 vs 0.65 ± 0.036 for line R), recipient line R had a better implantation rate (0.78 ± 0.033 vs 0.64 ± 0.036 for line A). Foetal survival was affected by the embryonic genotype. Embryos from donor line A had a higher foetal survival rate than embryos from donor line R (0.65 ± 0.036 vs 0.53 ± 0.038, respectively) but lower foetal and placenta weights. In conclusion, while embryonic genotype influenced both implantation and foetal survival rate, R embryos had the lowest rates, maternal genotype affected the implantation rate and R recipients may show a greater uterine receptivity during implantation period. Moreover, it must be observed that foetal and placenta weights were significantly affected by embryonic genotype and heavier for R line.     

Studies in sow reproduction: 5. The effect of lactation length of the so w on the subsequent embryonic development

The relative importance of factors causing a decrease in sow productivity with systems involving weaning of piglets under 3 weeks of age was studied. The observed reduction in litter size has been attributed to the ovulation rate or to embryo mortality. Subjects were 45 female pigs. 3 lactation lengths were tried: 7, 21, and 42 days. All sows were remated at the 1st postweaning estrus and slaughtered 20 days later to determine ovulation rate and embryo survival. All were fed 1.8 kg/day during gestation. During lactation, the feeding level was increased to a maximum of 6.3 kg/day depending on the number of piglets. Feed level from weaning to remating was 2.7 kg/day. Blood samples taken on 5 occasions from weaning to slaughter were assayed for progesterone. The weaning to estrous interval increased from 6.1 to 8.2 days when lactation length was reduced from 42 to 7 days. Ovulation rates, as determined by luteal count, were similar for the different periods of lactation. Numbers of viable embryos decreased significantly (p less than .05) as lactation length was reduced from 42 to 7 days. The survival of those embryos present decreased also (p less than .01). Embryo mortality increased from 17.3 to 40.4% when the lactation period was reduced from 42 to 7 days. Ovarian weights, uterine weights, and average embryo spacing were the same in all 3 groups. Plasma progesterone levels were low at weaning and remating, higher at 2 days postcoitum, and maximum at 10 days postcoitum. Between treatment groups, plasma progesterone levels were similar but varied markedly within treatment groups. Since ovulation rates were shown to be similar, this factor was eliminated. The interval from weaning to estrus was not considered important. Litter size was shown to be a major limiting factor. Embryo survival during the early period of gestation was shown to be the most important factor in limiting productivity.     

Integration of ovulation rate, potential embryonic viability and uterine capacity into a model of litter size in swine

A mathematical model of litter size in swine was developed from ovulation rate, potential embryonic viability and uterine capacity. The model assumed that ovulation rate was reduced to potentially viable embryos by factors innate to the ovum and embryo. Potentially viable embryos then could be further reduced to uterine capacity, the maximum number of fetuses that a female can carry to term. Consequently, litter size can be no greater than either ovulation rate or uterine capacity. Means and variances of ovulation rate and potential embryonic viability used in the model were based on experimental results. The mean and variance of uterine capacity were varied until the simulated mean and variance of litter size were equal to experimental results. Simulated results of relationships among ovulation rate, embryo survival and litter size were similar to observed experimental relationships. Heritabilities of simulated litter size and embryo survival were similar to literature values when the heritability of ovulation rate was set at .25 and the heritability of uterine capacity was set at either .15 or .20. Litter size was simulated for 25 combinations of average ovulation rate and uterine capacity to develop equations relating mean ovulation rate and uterine capacity to litter size, embryo survival and correlations among them. Results suggest that changing either ovulation rate or uterine capacity independently will not result in large changes in litter size. Consequently, the model suggests that a single gene, hormonal manipulation or nutritional change will not result in large increases in litter size and that combinations of factors will be needed to increase litter size.     

Early embryo survival and development in sows with lactational ovulation.

During lactation, daily separation of sow and piglets, intermittent suckling (IS), can induce lactational oestrus and ovulation. This study examined effects of IS on subsequent early embryo survival and development. Multiparous Topigs40 sows were separated from their piglets for either 12 consecutive hours per day (IS12, n = 13) or two times for 6 h per day (IS6, n = 10) from day 14 of lactation onwards until 23 days after ovulation. Control sows (C, n = 17) were weaned at day 21 of lactation. Oestrus was shown in all treatments within 5 days after the start of treatment. Sows were inseminated each day of oestrus and slaughtered at D23 after ovulation. Intermittent suckling did not significantly affect pregnancy rates of sows (75% IS12 vs 78% IS6 vs 94% C; p > 0.10). Embryo survival was not significantly affected by IS (IS12: 57%; IS6: 51%; p > 0.10) although it seemed to be lower than in C sows (70%). Some parameters of embryo, placental and uterine development were affected by IS, especially in the IS6 group. IS6 embryos had shorter placentas (17.5 +/- 1.2 cm; p < 0.05) than C (20.3 +/- 1.4 cm) and IS12 sows (20.9 +/- 0.7 cm) were smaller and less developed than C sows (p < 0.05). In conclusion, embryo survival does not seem significantly affected by IS, although numerical differences were great. Embryo development, however, was negatively affected in IS6 sows possibly due to a combination of high milk production, stress and lactational effects on uterine development.     

Divergent selection for uterine capacity in rabbits. II. Correlated response in litter size and its components estimated with a cryopreserved control population

Our objective was to evaluate the correlated responses to selection for litter size and its components after 10 generations of divergent selection for uterine capacity (UC). A total of 294 intact females from the 11th and 12th generations of divergent selection for high and low UC and from a cryopreserved control population was used (139, 112, and 43 females, respectively). Uterine capacity was assessed as litter size in unilaterally ovariectomized females. Traits recorded on females for up to five parities were litter size (LS) and number born alive (NBA). Laparoscopy was performed in all females at d 12 of their second parity, and the ovulation rate (OR) and number of implanted embryos (IE) were recorded in these females. Embryo survival (ES = IE/OR), fetal survival (FS = LS/IE), and prenatal survival (PS = LS/OR) were computed. Correlated responses in LS and in its components were inferred using Bayesian methods. Correlated responses in LS were asymmetric. The divergence between high and low lines was 2.35 kits, mainly because of a higher correlated response in the low line (1.88 kits). The lower LS in the low line was associated with a lower PS (control - low = 0.14), because of decreases in ES and FS.     

Divergent selection for uterine capacity in rabbits. III. Responses in uterine capacity and its components estimated with a cryopreserved control population

This work evaluated the response to 10 generations of divergent selection for uterine capacity (UC) in rabbits to determine whether this response was symmetric by contrasting both lines against a cryopreserved control population. Animals came from the 13th generation of an experiment of divergent selection for UC and from a cryopreserved control population. The two UC lines were divergently selected for 10 generations, and selection was relaxed from the 11th generation until the 13th generation. Uterine capacity was estimated as litter size (LS) in unilaterally ovariectomized (ULO) does. To create the control population, embryos from the base generation were vitrified and stored in liquid N2 for 10 generations. Data from 461 pregnancies produced by 134 ULO does were used: 62 does from the high UC line, 55 females from the low UC line, and 17 females from the control line. The following traits were analyzed: ovulation rate (OR); number of implanted embryos (IE); (UC), estimated as total number of rabbits born; number born alive (NBA); prenatal survival (PS), estimated as UC/OR; embryo survival (ES), estimated as IE/OR; and fetal survival (FS), estimated as UC/IE. Ovulation rate, IE, PS, ES, and FS were measured by laparoscopy only in the second parity. Uterine capacity and NBA were measured over four parities. Responses in UC and its components were estimated as differences between the selected lines and the control line using a Bayesian approach. Selection for UC led to differences of 1.01 kits between the high and low lines, but this response was asymmetric. No differences were found between the high and control lines (high - control = -0.08), whereas the low and control lines differed by 1.08 kits, with a probability of the difference being greater than zero of 0.98. Difference between the high and low lines and between the control and low lines was one-half of the difference reported for correlated response in LS in previous studies. No differences in OR were detected among lines. The control and low lines differed by 1.06 IE, with a probability of the difference being higher than zero of 0.84. Prenatal survival for the low line was less than that of the control line. In summary, selection for UC was asymmetric, which was mainly due to a correlated response in PS. Response in UC was one-half of the difference reported for correlated response in LS in previous studies.     

Transfer of pig embryos to different uterine sites.

Embryo transfer in pigs normally involves surgery. In connection with the development of nonsurgical or endoscopic transfer techniques, it is important to know whether the uterine site to which embryos are transferred has an effect on the success rate. In the present investigation, prepubertal donor gilts were treated with 1,500 IU of PMSG and, 72 h later, with 500 IU of hCG. Gilts were artificially inseminated 24 and 36 h after hCG injection. Embryos at the expanded blastocyst stage were collected from donor gilts. Recipient gilts were treated synchronous with the donors, using 1,000 IU of PMSG followed, 72 h later, with 500 IU of hCG. After a maximum of 3 h in vitro, embryos (n = 15 to 20, mean = 17.3) were transferred surgically to the middle of the uterine horn, to the caudal quarter of the uterine horn, or to the uterine body. Recipients were slaughtered between 28 and 34 d after transfer. The pregnancy rate of the recipients was low when the embryos were deposited in the uterine body (12%), compared with the middle (88%) or the caudal quarter of the uterine horn (81%) (P < .01). The corresponding average number of viable fetuses per pregnant recipient was 8.2 in the uterine body, 5.6 in the middle, and 4.5 in the caudal quarter. Average survival rate of embryos after transfer to the middle of the uterine horn was 41% vs 29 and 3% after transfer to the caudal quarter or the uterine body, respectively (P < .01). Hence, the uterine body seems to be an unsuitable site for embryo transfer in pigs. These results may explain the unsatisfactory results achieved with nonsurgical embryo transfer in the past.     

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.     

Effect of administration of phenylbutazone or progesterone on recovery of embryos from the uterus of mares 5 days after ovulation.

Twelve horse mares were used to investigate the effect of phenylbutazone or progesterone administration on uterine tubal motility, as reflected by embryo recovery from the uterus on day 5 after ovulation. Four treatment groups were used: group A (controls), in which uterine flush was performed 7 to 11 days after ovulation; group B (5-day controls), in which uterine flush was performed 5 days after ovulation; group C, in which uterine flush was performed 5 days after ovulation following administration of phenylbutazone (2 g, IV) on day 3; and group D, in which uterine flush was performed 5 days after ovulation following administration of progesterone in oil (250 mg, IM) on days 0, 1, and 2. Each mare was randomly assigned to each group once. Embryo recovery for each group was: group A, 13 embryos from 12 mares; group B, 3 embryos from 12 mares; group C, 4 embryos from 11 mares; and group D, 1 embryo from 11 mares. Recovery of embryos on day 5 in 3 of 12 nontreated mares indicated that equine embryos may enter the uterus before day 6. Neither treatment increased embryo recovery from the uterus on day 5 over that from the uterus of the 5-day controls.     

The effects of an advanced uterine environment on embryonic survival in the mare

Reasons for performing the study: During embryo transfer (ET) the equine embryo can tolerate a wide degree of negative asynchrony but positive asynchrony of >2 days usually results in embryonic death. There is still confusion over whether this is due to the inability of the embryo to induce luteostasis or to an inappropriate uterine environment. Objectives: To assess embryo survival and development in an advanced uterine environment. Hypothesis: Embryo–uterine asynchrony, not the embryo's inability to induce luteostasis, is responsible for embryonic death in recipient mares with a >2 days chronologically advanced uterus. Methods: Experiment 1: Thirteen Day 7 embryos were transferred to the uteri of recipient mares with luteal prolongation, occasioned by manual crushing of their own conceptus, such that donor–recipient asynchrony was between +13 and +49 days. Experiment 2: Day 7 embryos were transferred to recipient mares carrying their own conceptus at Days 18 (n = 2), 15 (n = 2), 14 (n = 4), 12 (n = 4) or 11 (n = 4) of gestation. In addition, Day 8 embryos were transferred to 4 pregnant recipient mares on Day 11 of gestation. Results: No pregnancies resulted following transfer of Day 7 embryos to recipients in prolonged dioestrus with asynchronies between +13 and +49 days. However, the use of early pregnant mares as recipients resulted in 5/20 (25%) twin pregnancies, 4 of which came from the transfer of a Day 8 embryo to a Day 11 recipient. All transferred embryos showed retarded growth, with death occurring in 4/5 (80%). Conclusions and potential relevance: The results emphasise the importance of an appropriate uterine environment for embryo growth and the inability of equine embryos to survive transfer to a uterus >2 days advanced even when luteostasis is achieved. It is possible that in normal, non‐ET equine pregnancy, embryo–uterine asynchrony may account for some cases of embryonic death.     

Some Factors Affecting the Rate of Pregnancy after Embryo Transfer Derived from the Brazilian Jumper Horse Breed

This study aimed to evaluate the effects of certain embryo transfer parameters on the pregnancy rate after equine embryo transfer of the Brazilian Jumper Horse breed. The size, embryonic development stage, embryo quality, and synchronization of ovulation between the donor (n = 120) and recipient (n = 420) were evaluated in 396 embryos. Embryo recovery was performed on Day 6-9 after ovulation (Day 0 = day of ovulation). The recipient mares were chosen on the day of embryo recovery, and the transfers were performed that same day. The embryo size (diameter including envelopes; n = 396) ranged from 150 to 3000 μm; 67.1% measured between 400 and 1199 μm. The embryo size (400-1199 μm vs. ≤399 μm); stage of development (n = 396; blastocyst and expanded blastocyst versus compact morula and early blastocyst); quality (n = 396; grade 1 [excellent]), 2 [good], or 3 [poor]); and synchronization of ovulation between the donor and recipient (0, 1, 2, 3, and 4 days versus −1, 5, and 6 days, respectively) all affected pregnancy rate (P < .05). The pregnancy rate did not differ significantly among transfers performed on Days 0, 1, 2, 3, and 4. In conclusion, embryos measuring 400-1199 μm produced higher pregnancy rates in recipients than embryos measuring 150-399 μm, and blastocysts and expanded blastocysts produced pregnancy more efficiently than morulae and early blastocysts. The embryo quality also affected the pregnancy rate. Synchronization of donor and recipient ovulation to Days 0-4 improved the efficiency of embryo transplant.     

Selection for ovulation rate in rabbits

An experiment of selection for ovulation rate was carried out. Animals were derived from a synthetic line first selected 12 generations for litter size, then 10 generations for uterine capacity. Selection was relaxed for 6 generations. Selection was based on the phenotypic value of ovulation rate with a selection pressure on does of 30%. Males were selected from litters of does with the highest ovulation rate. Males were selected within sire families in order to reduce inbreeding. Ovulation rate was measured in the second gestation by a laparoscopy, 12 days after mating. Each generation had about 80 females and 20 males. Results of three generations of selection were analyzed using Bayesian methods. Marginal posterior distributions of all unknowns were estimated by Gibbs sampling. Heritabilities of ovulation rate (OR), number of implanted embryos (IE), litter size (LS), embryo survival (ES), fetal survival (FS), and prenatal survival (PS) were 0.44, 0.32, 0.11, 0.26, 0.35, and 0.14, respectively. Genetic correlation between OR and LS was 0.56, indicating that selection for ovulation rate can augment litter size. Response to selection for OR was 1.80 ova. Correlated responses in IE and LS were 1.44 and 0.49, respectively. Selection for ovulation rate may be an alternative to improve litter size.     

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.     

Effect of feeding allowance level on embryonic survival, IGF-1, insulin, GH, leptin and progesterone secretion in early pregnancy gilts

The present experiment was conducted to evaluate the effects of feeding allowance level on embryonic survival, uterine development and reproductive hormone secretion in early gestation gilts. A total of 54 F1 crosses of Landrace x Large white gilts were randomly allocated to three treatment groups of high (H, 2 x maintenance), medium (M, 1.2 x maintenance) and low (L, 0.6 x maintenance) feeding level after mating. Blood samples and uterine flushings were collected on day 12, 25 and 35 of pregnancy, and embryonic survival rate was estimated. Concentrations of insulin-like growth factor I (IGF)-1, insulin, growth harmone (GH), leptin and progesterone in serum and uterine flushings were determined by enzyme-linked immunosorbent assay. Embryonic survival was affected by dietary treatment; total number of viable embryos and embryo survival of group M were higher than other groups in the early pregnancy (p < 0.05). Greater foetal weight in M gilts was achieved when gestation advanced to day 35 (p < 0.05), though there was no difference on day 25 of pregnancy among treatments. No appreciable differences were observed in the crown-rump length on day 25 and 35 of pregnancy among groups. Greater weight of uterus and products of conception were identified in M gilts compared with group H and L (p = 0.024 and p = 0.005, respectively) on day 25 of pregnancy. The hormone level was greatly affected by feeding allowance level. In serum, concentrations of IGF-1, leptin and insulin tended to be greater in H than in M and L during the early gestation, while concentrations of GH were greater in M and progesterone were the lowest in H. At the same time, feed allowance level affected the concentration of IGF-1, insulin, GH, leptin and progesterone in uterine flushings. These data demonstrated that feed allowance level after mating has important consequence on embryo survival, embryo development and uterine development, possibly mediated by nutrition level inducing changes in concentrations of reproductive hormones and/or intermediary metabolites in early pregnancy.     

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.     

Historical Aspects of Equine Embryo Transfer

Early embryo transfer in equids was undertaken simultaneously in the early 1970s in Cambridge, England, and Kyoto, Japan. Both groups achieved limited success when flushing the uterine horn ipsilateral to the side of ovulation but the rates improved markedly when the whole uterus was flushed on realization of the continued movement of the embryo throughout the uterine lumen after day 6. Initial transfers of embryos to recipient mares were carried out surgically, but nonsurgical transfer via the cervix has been used subsequently with increasing success, culminating in pregnancy rates of 75%–90% today. Experimental use of embryo transfer in horses and donkeys demonstrated the unique ability of equids to carry to term a full range of interspecies hybrid conceptuses and extraspecies pregnancies created by embryo transfer. Furthermore, splitting of day 4–8 cell embryos and day 6 compact morulae allowed the creation of genetically identical twin foals. But despite these and other significant advances over the past 45 years, a persisting limitation is the relatively low embryo recovery rates from donor mares treated with exogenous gonadotropins in attempts to induce them to superovulate. This is due to the toughness of the ovarian tunica albuginea which forces ovulation through the ventrally situated ovulation fossa where multiple follicles compete with each other and luteinize before they can ovulate properly.     

Selection for components of reproduction in swine

The response per generation to 10 generations of mass selection for ovulation were 0.49 ova, ?1.6% in embryo survival and 0.06 piglets per litter at birth. Line differences (select-control) in generation 9 and 10 gilts and sows ranged from 3.4 to 5 ova. Control line gilts and sows had 5.4 to 10.6% higher embryo survival to days 30 and 70 of gestation than did select line females. One generation of random selection followed by four generations of litter size selection, selection for decreased age at puberty or relaxed ovulation rate selection in the high ovulation rate line has resulted in lines that differed from the control line in litter size at birth by 0.78 ± 0.22, 0.37 ± 0.39 and 0.84 ± 0.52 pigs per litter at first, second and third parity, respectively. These results were used to derive a selection index to increase litter size by selection for its components (ovulation rate, OR, and embryo survival, ES). A technique of selection based on laparotomy to increase the number of females tested with a given set of farrowing places is presented. Rate of response in LS from use of the selection index, I = 10.6 OR + 72.6 ES, in a population of 40 farrowing females and 15 males per generation, is expected to increase litter size 2.5 times faster than selection on LS due to higher selection intensity and optimum emphasis on the component traits.