Relationships between ovulation rate and embryonic and placental characteristics in multiparous sows at 35 days of pregnancy

Experiences with transvaginal Ovum Pick-Up (OPU) in sows

Transvaginal ultrasound-guided Ovum Pick-Up (OPU) is an established technique in other species. Due to several challenges, there are few publications addressing the procedure in sows. An efficient OPU technique may allow for the collection of numerous oocytes from valuable sows for porcine in vitro embryo production, gene editing and cloning programmes, or cryopreservation. We aimed to improve transvaginal OPU and equipment for this technique in sows. In experiment 1, we conducted 13 OPU sessions on three Landrace x Large White hybrid sows under general anaesthesia, while the second experiment explored OPU in non-sedated animals (N = 6) physically restrained in a commercial claw trimming chute. The experiments resulted in 6.6 ± 5.6 (mean ± SD) and 7.7 ± 8.9 recovered cumulus-oocyte complexes per session, respectively. Post-mortem examination of the pelvic and abdominal cavities of the three sows subjected to repeated OPU sessions did not reveal major acute or chronic pathological lesions. The only sow which was inseminated after the experiment delivered 16 liveborn piglets at term. Salivary cortisol levels increased during the procedure in non-sedated and physically restrained sows but returned to baseline 1 h later (n = 5), indicating a short-term stress response. The described OPU technique and equipment have the potential to retrieve considerable numbers of oocytes by repeated procedures on valuable mature sows. Follow-up studies are needed to optimize the efficiency of the aspiration of high-quality oocytes and to describe the developmental competence of these OPU-derived oocytes. It is also essential to further investigate sow welfare during and after the procedure before recommending porcine transvaginal OPU as a sustainable and welfare-friendly procedure.

Standardized ileal digestible lysine requirement of pregnant sows under commercial conditions

OBJECTIVE

The present experiment aimed to determine standardized ileal digestible (SID) lysine (Lys) requirements for pregnant sows individually housed under commercial farm conditions.

METHODS

Two hundred multiparous sows (parity = 5.1±2.0) on day 42 of gestation were randomly allocated to five dietary treatments with a balanced parity. Experimental diets were formulated to contain 0.22%, 0.32%, 0.42%, 0.52%, and 0.62% of SID Lys for the mid-gestation period (days 42 to 76) and 0.36%, 0.46%, 0.56%, 0.66%, and 0.76% of SID Lys for the late gestation period (days 77 to 103). All indispensable amino acids except Lys were provided at 110% of their requirement estimates. Daily feed allowance per sow was determined based on the back-fat thickness and body condition score at the second pregnancy check and on day 90 of gestation. Three different statistical models were used to estimate the SID Lys requirement.

RESULTS

Total born piglets alive per litter increased linearly and quadratically (p<0.001) as dietary SID Lys increased. For total born piglets alive per litter, the SID Lys requirement estimates ranged from 9.69 to 12.4 g/d for the mid-gestation period (1.19 to 1.52 g/Mcal metabolizable energy; 0.39% to 0.49%) and 14.6 to 17.4 g/d for the late gestation period (1.62 to 1.93 g/Mcal metabolizable energy; 0.52% to 0.62%).

CONCLUSION

The mean values of the SID Lys requirement for the mid-gestation period and the late gestation period are 11.1 and 16.1 g/d (1.36 and 1.79 g/Mcal metabolizable energy; 0.44% and 0.58%), respectively, for maximal total born piglets alive per litter.

Effects of dietary coenzyme Q10 supplementation during gestation on the embryonic survival and reproductive performance of high-parity sows

BACKGROUND

Fertility declines in high-parity sows. This study investigated whether parity-dependent declines in embryonic survival and reproductive performance could be restored by dietary coenzyme Q10 (CoQ10) supplementation.

METHODS

Two experiments were performed. In Exp. 1, 30 young sows that had completed their 2^nd parity and 30 high-parity sows that had completed their 10^th parity, were fed either a control diet (CON) or a CON diet supplemented with 1 g/kg CoQ10 (+ CoQ10) from mating until slaughter at day 28 of gestation. In Exp. 2, a total of 314 post-weaning sows with two to nine parities were fed the CON or + CoQ10 diets from mating throughout gestation.

RESULTS

In Exp. 1, both young and high-parity sows had a similar number of corpora lutea, but high-parity sows had lower plasma CoQ10 concentrations, down-regulated genes involved with de novo CoQ10 synthesis in the endometrium tissues, and greater levels of oxidative stress markers in plasma and endometrium tissues. High-parity sows had fewer total embryos and alive embryos, lower embryonic survival, and greater embryo mortality than young sows. Dietary CoQ10 supplementation increased the number of live embryos and the embryonic survival rate to levels similar to those of young sows, as well as lowering the levels of oxidative stress markers. In Exp. 2, sows showed a parity-dependent decline in plasma CoQ10 levels, and sows with more than four parities showed a progressive decline in the number of total births, live births, and piglets born effective. Dietary supplementation with CoQ10 increased the number of total births, live births, and born effective, and decreased the intra-litter covariation coefficients and the percentage of sows requiring farrowing assistance during parturition.

CONCLUSIONS

Dietary CoQ10 supplementation can improve the embryonic survival and reproductive performance of gestating sows with high parity, probably by improving the development of uterine function.

Managing Reproduction in Hyperprolific Sow Herds

The rearing of large litters from hyperprolific sows is a characteristic of modern genotypes. However, these sows have body and reproductive characteristics that differentiate them from the genotypes of the past decades, making it necessary to adopt different management strategies. This review describes the main care and challenges associated with the hyperprolificity of sows during the period in which replacement gilts are selected, along with gestation, parturition, lactation, and the weaning-estrus interval. It describes the challenges that these sows' piglets will face during the lactation period and includes some strategies adopted to develop these surplus piglets. In addition, it identifies areas where more research is needed to understand the reproductive management of modern genotypes.

Fetal and placental development in early gestation of hyper-prolific sows

Modern hyper-prolific sows produce large litters with a high within-litter variation in birth weight and an increased number of low-birth-weight piglets per litter with higher mortality rates and lower growth rates compared to heavier littermates. This study aimed to describe fetal development in hyper-prolific sows, to characterize differences between large and small fetuses, and to determine when within-litter variation in fetal weight can be detected. Forty-seven multiparous sows were blood-sampled and slaughtered at day 28, 33, 45, 50, and 56 of gestation. Number of fetuses were counted, fetal body and organ weights were measured, and the intrauterine positioning was recorded. Length, width, and area of each placenta was measured and the fetus weight/placental weight ratio was calculated. The umbilical cords of the smallest, medium and the largest fetus of each litter were sampled for histological analysis. In total measurements were obtained for 1161 fetuses. The results revealed no difference in fetal survival between the gestational days (P > 0.05). Intrauterine positioning near the cervix significantly reduced fetal weight at day 56 (P < 0.05). Total litter weight and average fetal weight increased with gestational age and individual fetal weight was negatively affected by litter size from day 33 and onwards (P < 0.05). The coefficient of variation for within-litter variation in fetal weight was higher at day 28 compared to the other gestational days (P < 0.05). Relative brain- and heart weights decreased from day 28-56 (P < 0.001). Small fetuses had relatively heavier brains and hearts at day 45, 50 and 56 (P < 0.001). Size of placenta, fetus weight/placental weight ratio and length of umbilical cord increased with gestational age (P < 0.001). There was a positive correlation between size of placenta and weight of individual fetus (P < 0.001), the weight of the fetus was positively correlated with umbilical cord length (P < 0.001) and the umbilical cross-sectional area was correlated to fetal weight at day 56 (P < 0.01). Individual fetal weight was positively correlated to the fetus weight/placental weight ratio (P < 0.001). In conclusion, fetal growth was affected by litter size, placental weight, and -area, and umbilical cord length. Lightweight fetuses were characterized by having placentas with lower weight and area and shorter umbilical cords. Lastly, within-litter variation in fetal weight was detectable at day 28, and the coefficient of variance remained stable from day 33-56.

The influence of litter birth weight phenotype on embryonic and placental development at day 30 of gestation in multiparous purebred Large White sows

The aim of this study was to understand the intrauterine biological processes associated with the low litter birth weight phenotype in pigs. Analyses were conducted on reproductive data from a purebred Large White maternal line to identify sows (>2 parities) with repeatable high or low litter birth weight phenotype (HLBWP or LLBWP). A total of 40 sows were selected (n = 20 HLBWP and n = 20 LLBWP) and bred with semen from purebred Large White boars of proven fertility. Sows were euthanized on day 28-30 of gestation (day 29.5 ± 0.6) and samples of placenta and embryos collected. Total number of embryos (TNE), embryonic weight (EW), embryonic viability, and crown-rump (CRL) measurements were recorded, along with the ovulation rate (OR) and allantochorionic fluid volume (AFV). No significant difference was detected (P > 0.05) in OR, TNE, and number of viable embryos on day 30 of gestation between the two groups. There was no significant difference in EW (LLBWP: 0.80 ± 0.05 g; HLBWP: 0.88 ± 0.04 g, P = 0.18) or CRL (LLBWP: 21.5 ± 0.7 mm; HLBWP: 21.9 ± 0.68 mm, P = 0.46). Placental development represented by the average AFV was significantly lower in the LLBWP compared to HLBWP (LLBWP: 131 ± 9.82 mL; HLBWP: 149 ± 9.39 mL, P = 0.03). In conclusion, placental development may be the main factor causing lower BW of entire litters in LLBWP sows.

Altrenogest Supplementation during Early Pregnancy Improves Reproductive Outcome in Pigs

Progesterone plays an important role in initial conceptus development and in a successful pregnancy, but results related to progesterone or its analogues (altrenogest) supplementation in early pregnancy of pigs are conflicting. The present study evaluated the effects of altrenogest supplementation in sows during days 6 and 12 of pregnancy on reproductive performance. On day 6 of pregnancy, 301 females were allocated at random to one of the following treatments: CON (Control: non-supplemented females, n = 163) or ALT (females daily supplemented with 20 mg of altrenogest, orally, from day 6 to 12 of pregnancy, n = 138). Ovulation was considered as occurred at 48 h after the first estrus detection to standardize the first day of pregnancy. The supplementation increased the number of total piglets born (ALT: 17.3 ± 0.4; CON: 16.6 ± 0.4), piglets born alive (ALT: 15.6 ± 0.4; CON: 14.8 ± 0.3), and placenta weight (ALT: 4.2 ± 0.1; CON: 3.8 ± 0.1) and decreased the stillbirth rate (ALT: 5.9 ± 0.6; CON: 7.6 ± 0.6) and the number of piglets born weighing less than 800 g (ALT: 6.6 ± 0.6; CON: 8.0 ± 0.6), without impairment on farrowing rate. These results demonstrated that altrenogest supplementation on swine females between days 6 and 12 of pregnancy may be used to improve reproductive performance.

Leucine supplementation during late gestation globally alters placental metabolism and nutrient transport via modulation of the PI3K/AKT/mTOR signaling pathway in sows

In a previously published study we reported that sow dietary leucine supplementation during late pregnancy significantly improved newborn piglet birth weight by stimulating protein synthesis in the longissimus dorsi muscle. However, there is still limited knowledge as to whether leucine can exert its effects on the placenta, one of the most important temporal organs during pregnancy, to promote maternal-fetal nutrient supply and thus contribute to fetal intrauterine development. Therefore, we tested this hypothesis in the present study. In total, 150 sows at day 90 of gestation were divided into three groups and fed with either a control diet (CON), CON + 0.4% Leu or CON + 0.8% Leu, respectively, until parturition. Placental metabolomics, full spectrum amino acids and nutrient transporters were systematically analyzed after sample collection. The results indicated that Leu supplementation led to an altered placental metabolism with an increased number of metabolites related to glycolysis and the oxidation of fatty acids, as well as elevated levels of amino acid accumulation in the placenta. In addition, nutrient transporters of amino acids, glucose and fatty acids in the placenta were globally up-regulated and several enzymes related to energy metabolism, including hexokinase, succinate dehydrogenase, lactated hydrogenase, glycogen phosphorylase and hydroxyacyl-CoA-dehydrogenase, were also significantly increased with no change observed in the antioxidative status of those groups with Leu supplementation. Furthermore, the phosphorylation of PI3K, Akt, and mTOR was enhanced in the placenta of sows undergoing Leu treatment. Collectively, we concluded that supplementing the diets of sows with Leu during late gestation globally altered placental metabolism and promoted maternal-fetus nutrient transport (amino acids, glucose, and fatty acids) via modulation of the PI3K/Akt/mTOR signaling pathway.

Pregnancy in pigs: the journey of an early life

Embryo mortality is responsible for greater losses in litter size in pigs. It is well known that pregnancy establishment is a complex process, and important changes occur continuously in both the corpora lutea and the endometrium, which varies depending on the pre-natal development phase: embryonic, pre-implantation or fetal stages. The placenta is a key organ responsible for the exchange of nutrients, metabolites and respiratory gases between mother and fetuses. The porcine placenta is diffuse, epitheliochorial, and placentation begins with implantation, which involves specialized cell adhesion and cell migration, leading to the attachment of the trophectoderm to the uterine endometrial lumen epithelium. The efficiency with which the placenta provides adequate amounts of nutrients and oxygen to the fetus is crucial for proper fetal growth and development. In the last decades, emphasis on selection for sow prolificacy has resulted in a substantial increase in the number of piglets born per litter, which had a direct effect on piglet quality, compromising birth weight and litter uniformity. Placental insufficiency will lead to fetal intrauterine growth restriction. This review addresses the main events of early embryo development, including preimplantation and implantation periods. In addition, placentation and its role on fetal development are covered, as well as intrauterine growth restriction, as it is a natural condition in the pig, with long lasting detrimental effects to the production chain.

Effects of cooling systems on physiological responses and intestinal microflora in early gestating sows exposed to high-temperature stress

This study was conducted to investigate the effect of cooling systems on reproductive performance, body temperature, blood metabolites, and the intestinal microbiome in early gestating sows exposed to high ambient temperature. In total, 39 pregnant sows (Landrace × Yorkshire; 2 parities) were randomly assigned to and maintained in the following three treatment groups (13 sows per group) over days 0 to 35 of pregnancy: (i) air cooling (AC; 26.87 ± 1.23°C), (ii) water-drip cooling (WC; 28.81 ± 0.91°C), and (iii) a lack of cooling with heat stress (HS; 30.72 ± 0.70°C). Backfat thickness was measured before and after HS. Feces were collected on day 0 and 35 d of the trial for microbiome analysis, whereas blood was taken at day 35 of pregnancy and analyzed. Reproductive performance and physiological responses were identified at day 35. Respiration rate along with rectal and skin temperatures were lower (p < 0.05) in the AC group than in the HS and WC groups. Serum blood urea nitrogen values were increased (p < 0.05) in the WC group compared with those measured in the AC and HS groups. Triiodothyronine was found at greater levels (p < 0.05) in the AC than in the HS group. Reproductive performance was not affected by the cooling systems. At the phylum level, fecal pathogenic Spirochaete and Euryarchaeota were found in higher numbers (p < 0.05) in all groups after HS. Similarly, at the genus level, the amount of Treponema was greater (p < 0.05) in all groups after HS. In conclusion, our results suggest that AC or WC can ameliorate or mitigate the adverse effects of HS on the physiological parameters of pregnant sows reared under high temperatures.

Consequences of negative energy balance on follicular development and oocyte quality in primiparous sows†

Metabolic demands of modern hybrid sows have increased over the years, which increases the chance that sows enter a substantial negative energy balance (NEB) during lactation. This NEB can influence the development of follicles and oocytes that will give rise to the next litter. To study effects of a lactational NEB on follicular development, we used 36 primiparous sows of which 18 were subjected to feed restriction (3.25 kg/day) and 18 were full-fed (6.5 kg/day) during the last 2 weeks of a 24.1 ± 0.3 day lactation. Feed restriction resulted in a 70% larger lactational body weight loss and 76% higher longissimus dorsi depth loss, but similar amounts of backfat loss compared to the full fed sows. These changes were accompanied by lower plasma insulin-like growth factor 1 (IGF1) and higher plasma creatinine levels in the restricted sows from the last week of lactation onward. Ovaries were collected 48 h after weaning. Restricted sows had a lower average size of the 15 largest follicles (−26%) and cumulus–oocyte complexes showed less expansion after 22 h in vitro maturation (−26%). Less zygotes of restricted sows reached the metaphase stage 24 h after in vitro fertilization and showed a higher incidence of polyspermy (+89%). This shows that feed restriction had severe consequences on oocyte developmental competence. Follicular fluid of restricted sows had lower IGF1 (−56%) and steroid levels (e.g., β-estradiol, progestins, and androgens), which indicated that follicles of restricted sows were less competent to produce steroids and growth factors needed for oocytes to obtain full developmental competence.

Fertility responses of melatonin-treated gilts before and during the follicular and early luteal phases when there are different temperatures and lighting conditions in the housing area

This study was conducted to determine whether exogenous melatonin affected gilt fertility when there were different housing temperature and lighting conditions. Prepubertal gilts (n = 72) were fed (MEL, 5 mg/day) or not fed (CON) melatonin while housed in rooms where temperatures (31.0 ± 1 °C) and daily lighting (240 lx) duration differed: 8 (8 H); 16 (16 H); or 24 (24 H) h in winter and summer replicates. Gilts were moved into rooms (day 1) and administered PG600 on day 6. Gilts detected in estrus were inseminated and slaughtered on day 33 of gestation to determine pregnancy and litter responses. There was no treatment x room effect on estrus (77.8 %), follicle sizes, or number of corpora lutea, but MEL-treated gilts had a longer (P = 0.02) estrous duration (2.0 d) than gilts of the CON (1.7 d) group. Pregnancy rate (92.6 %) and embryo number (13.5) were not affected by treatment or room conditions. There was a treatment x room effect, however, with embryo survival being less (P =  0.01) by ∼23 % in gilts of the CON-24H than CON-16H, MEL-8H, and MEL-24H groups. In the summer replicate, there were also fewer large follicles, a lesser estrous detection percentage, viable embryos, and embryo survival rate than during the winter (P < 0.05). Overall, MEL treatment had positive effects on estrous duration and embryo survival, especially in the summer when there were varying lighting regimens and room temperatures in which gilts were housed.

Profiling circulating microRNAs in the serum of pregnant and non-pregnant pigs reveals a plethora of reproductive status-dependent microRNAs

Circulating, non-coding RNAs, such as microRNAs (miRNAs) have been proposed to be powerful pathophysiological indicators of pregnancy in animals and humans. Since their discovery, it is known that miRNAs can take part in numerous biological processes, including cell proliferation and differentiation during early embryonic development and establishment of pregnancy. Our recent studies have indicated that maternal blood can carry miRNAs reported previously at the embryo-maternal interface in pigs. To expand the scope of our research, we tested the hypothesis that miRNAs previously identified in conceptuses, trophoblasts, endometrium and uterine lumen-derived extracellular vesicles (EVs) collected before Day 20 of pregnancy can show reproductive status-dependent profiles in the serum of cyclic and pregnant crossbred pigs. Custom-designed TaqMan arrays, multiplex real-time reverse transcription (RT)-PCR and real-time RT-PCR allowed us to identify a number of reproductive status-dependent miRNAs in serum samples collected from pigs during the estrous cycle or pregnancy (Days 16 and 20). We found that serum samples were enriched with miRNAs involved in processes important during the estrous cycle and early pregnancy, e.g. cell sensitivity and viability, angiogenesis, embryonic cell proliferation and differentiation. Further validation revealed different abundance of ssc-miR-143-3p and ssc-miR-125b in pregnant and non-pregnant animals and correlation of ssc-miR-125b levels with litter size. In addition, analyzed serum samples contained both EVs and Argonaute2 proteins, which are known to be involved in miRNA transportation and intercellular communication. In summary, we identified several circulating miRNAs that differ in abundance between cyclic and pregnant animals and could serve as potential indicators of reproductive status in pigs during breeding management.

Coping with large litters: the management of neonatal piglets and sow reproduction

As a result of intensive breeding, litter size has considerably increased in pig production over the last three decades. This has resulted in an increase in farrowing complications. Prolonged farrowing will shorten the window for suckling colostrum and reduce the chances for high-quality colostrum intake. Studies also agree that increasing litter sizes concomitantly resulted in decreased piglet birth weight and increased within-litter birth weight variations. Birth weight, however, is one of the critical factors affecting the prognosis of colostrum intake, and piglet growth, welfare, and survival. Litters of uneven birth weight distribution will suffer and lead to increased piglet mortality before weaning. The proper management is key to handle the situation. Feeding strategies before farrowing, management routines during parturition (e.g., drying and moving piglets to the udder and cross-fostering) and feeding an energy source to piglets after birth may be beneficial management tools with large litters. Insulin-like growth factor 1 (IGF-1)-driven recovery from energy losses during lactation appears critical for supporting follicle development, the viability of oocytes and embryos, and, eventually, litter uniformity. This paper explores certain management routines for neonatal piglets that can lead to the optimization of their colostrum intake and thereby their survival in large litters. In addition, this paper reviews the evidence concerning nutritional factors, particularly lactation feeding that may reduce the loss of sow body reserves, affecting the growth of the next oocyte generation. In conclusion, decreasing birth weight and compromised immunity are subjects warranting investigation in the search for novel management tools. Furthermore, to increase litter uniformity, more focus should be placed on nutritional factors that affect IGF-1-driven follicle development before ovulation.

An investigation into uterine capacity based on litter and placental characteristics in two sow lines with different prolificacy (Danish Landrace x Danish Yorkshire versus German Saddleback)

Litter size in modern so called hyperprolific pig (Sus scrofa Linnaeus) breeds such as of crossbred Danish Landrace x Danish Yorkshire (LY/YL) sows increased remarkably over recent years, however, commonly associated with reduced piglet birth weight and higher within litter birth weight variability likely due to a limited uterine capacity. Since investigation into this issue is patchy, the aim of this study was to investigate uterine capacity based on litter and placental characteristics in two sow lines with different prolificacy, that is crossbred Danish genetic (Danish Landrace x Danish Yorkshire; DG; n = 14) and purebred German Saddleback (GS) sows (n = 12). Parameters recorded were litter size, piglet birth weight and vitality, placental weight and surface area as well as placental vascularization. Litters of DG were on average larger than of GS (p < .001). Piglets of DG weighed on average less than GS (p < .001) and were less vital (p < .001-.142). Increasing litter size was associated with reduced piglet birth weight and increased within litter birth weight variability in GS, but not in DG. DG had on average a lower placental weight (p < .001) and smaller placentae (p < .001) than GS, but the placenta was on average more efficient than of GS (based on the quotient of piglet and corresponding placental weight; p < .001). Vascularization of placentae was on average not or only slightly different between breeds (p < .05 - .982). Remarkably, however, vascularization of the lateral and apical chorionic epithelium of the chorionic ridges as the immediate foetal/maternal interface was on average slightly higher in DG than GS (p < .05-.111). Results thus demonstrate that uterine capacity based on litter and placental characteristics is higher in DG than GS sows.

Associations among individual gilt birth weight, litter birth weight phenotype, and the efficiency of replacement gilt production

Selection for larger litter size has increased the number of low individual birth weight (BWi) pigs and produced sows with a repeatable low average litter birth weight phenotype (BWP). Using an average of 3.6 litters records per sow, BWP was established in 644 nucleus-multiplication sows producing replacement gilts in a large commercial operation and classified as low (L-BWP, <1.18 kg, n = 85), medium (M-BWP, ≥1.18 to ≤1.35 kg, n = 250), or high (H-BWP, >1.35 kg, n = 309) on the basis of a BWi of 1.18 kg below which there was a high risk of early mortality and the average BWi (1.35 kg) for the population. In subsequent litters, potential replacement gilts born to these sows (n = 7,341) received a unique identification tag that allowed the impact of BWi, BWP, and their interactions on the efficiency of replacement gilt production to be evaluated. Negative effects of BWi on mortality until day 4 after birth were confirmed (P < 0.05) and cumulative losses to weaning, to day 70 of age, and to final pre-selection at 165 d of age were affected (P ≤ 0.05) by the interaction between BWP and BWi. Among the 2,035 gilts for which records for selection efficiency and production to fourth parity were available, a lower BWi decreased the probability of gilts reaching pubertal estrus (P < 0.05) after 21 and 28 d of boar stimulation starting at 180 d of age, with no effect of BWP. Overall, neither BWi, BWP, nor their interaction affected age at puberty. After breeding, only the main effect of BWP affected productivity and retention in the sow herd. In parities 1 and 2, percent stillborn was higher in litters born to gilts from H-BWP compared with L-BWP dams (P < 0.05), and in parity 2, total born and born alive were lower in sows derived from H-BWP compared with other BWPs. There were no differences in retention based on BWP classes until parity 2, after which retention tended (P ≤ 0.09) to be lower in sows derived from H-BWP compared with L-BWP dams. These results provide evidence that sow BWP is an important factor in the overall efficiency of replacement gilt management. This study also confirms that effective gilt selection and pre-breeding management protocols support excellent sow lifetime productivity and mitigate the risk of a high BWP in the litter of origin affecting retention in the breeding herd.

Effects of flush feeding strategy before breeding on reproductive performance of modern replacement gilts: impacts on ovulation rate and litter traits

AbstractThe effects of two feed levels offered during two estrous cycles before insemination were evaluated on the reproductive performance of gilts. A total of 93 gilts (PIC Hendersonville, TN) were individually housed and manually fed twice a day with 2.1 or 3.6 kg/d of a corn and soybean meal-based diet (3.15 Mcal ME/kg and 0.64% standardized ileal digestible lysine), during two estrous cycles before breeding (cycle 1, between first and second estrus; cycle 2, between second and third estrus). Gilts were weighed at the beginning of the experiment, at second and third estrus, and at slaughter (30.2 ± 1.2 d of gestation). Follicles were counted at second estrus, and the embryo-placental units and the corpora lutea were individually counted, measured, and weighed at slaughter. Gilts fed 3.6 kg/d had greater BW gain during cycle 1 and cycle 2 (P < 0.001; + 9.8 kg and + 10.0 kg, respectively) becoming heavier at second and third estrus (P < 0.001). At second estrus, gilts fed 3.6 kg/d had 1.6 more medium-large follicles (P = 0.074) but no difference in follicle size (P = 0.530) was observed. Gilts fed 3.6 kg/d in cycle 1 or cycle 2 had a greater ovulation rate at third estrus (P < 0.016) than those receiving 2.1 kg/d. Also, 3.6 kg/d in cycle 2 increased early embryo mortality (P = 0.006; 2.3 vs. 1.1 dead embryos) and consequently reduced total embryo survival (P = 0.002; 84.6 vs. 90.1%). Gilts fed 3.6 kg/d during cycle 1 had two more total embryos (P < 0.001; 17.2 vs. 15.1) and two more vital embryos on day 30 (P < 0.001; 16.7 vs. 14.5) in comparison with gilts fed 2.1 kg/d. The coefficient of variation for placental length was greater for gilts fed 3.6 kg/d during cycle 1 (P = 0.003). No further significant effects of feeding levels were observed on embryo and placental traits (P ≥ 0.063). These results suggest that the feeding level during the first cycle after pubertal estrus is crucial to set ovulation rate and potential litter size for breeding at next estrus. However, flush feeding gilts before insemination can negatively impact litter size by reducing embryo survival when breeding at third estrus.

Effects of oestrous synchronization with altrenogest in gilts on endometrial and embryonic characteristics

The use of altrenogest (ALT) supplementation for oestrous synchronization improves subsequent reproductive performance of gilts and sows. However, the causes of this improvement in reproductive performance after ALT treatment are not fully/clearly understood. The objective of this study was to evaluate the effects of ALT supplementation for oestrous synchronization in gilts on the endometrial glands and embryonic development characteristics at 28 days of pregnancy. Pregnant gilts were divided into two experimental treatments: Control (did not receive ALT; n = 9 gilts) and ALT (ALT feeding at 20 mg/day for 18 days; n = 9 gilts). At 28 days of pregnancy, six gilts from each treatment were slaughtered, and reproductive tracts were immediately evaluated. There was no statistical difference (P > 0.05) between treatments regarding ovulation rate, number of embryos, number of vital embryos and number of non-vital embryos. Embryo weight, length and embryonic vesicle weight were lower in ALT treatment compared with Control (P < 0.01), and it was lower in the cervical uterine region compared with apex uterine region, respectively (P < 0.05). Higher values of gland duct area, gland duct perimeter, percentage of the glandular area and total endometrial area were observed in ALT treatment compared with Control (P < 0.05). The use of ALT during 18 days for oestrous synchronization in gilts increased the gland duct area, perimeter and total endometrial area but did not increase the embryo number and embryo size at day 28 of pregnancy.

Gene Expression Profiling of Corpus luteum Reveals Important Insights about Early Pregnancy in Domestic Sheep

The majority of pregnancy loss in ruminants occurs during the preimplantation stage, which is thus the most critical period determining reproductive success. Here, we performed a comparative transcriptome study by sequencing total mRNA from corpus luteum (CL) collected during the preimplantation stage of pregnancy in Finnsheep, Texel and F1 crosses. A total of 21,287 genes were expressed in our data. Highly expressed autosomal genes in the CL were associated with biological processes such as progesterone formation (STAR, CYP11A1, and HSD3B1) and embryo implantation (e.g., TIMP1, TIMP2 and TCTP). Among the list of differentially expressed genes, sialic acid-binding immunoglobulin (Ig)-like lectins (SIGLEC3, SIGLEC14, SIGLEC8), ribosomal proteins (RPL17, RPL34, RPS3A, MRPS33) and chemokines (CCL5, CCL24, CXCL13, CXCL9) were upregulated in Finnsheep, while four multidrug resistance-associated proteins (MRPs) were upregulated in Texel ewes. A total of 17 known genes and two uncharacterized non-coding RNAs (ncRNAs) were differentially expressed in breed-wise comparisons owing to the flushing diet effect. The significantly upregulated TXNL1 gene indicated potential for embryonic diapause in Finnsheep and F1. Moreover, we report, for the first time in any species, several genes that are active in the CL during early pregnancy (including TXNL1, SIGLEC14, SIGLEC8, MRP4, and CA5A).

Maternal nutrition during early and late gestation in gilts and sows under commercial conditions: impacts on maternal growth and litter traits1

The effects of two different feeding levels, offered in two phases during gestation, on body measurements and litter traits were evaluated in 152 gilts and 551 sows. The treatments consisted of the combination of two gestation phases (phase 1-days 22 to 42; phase 2-days 90 to 110) and two feed amounts (1.8 or 3.5 kg/d). Females were weighed on days 22, 42, 90, and 110 of gestation. Born alive and stillborn piglets were weighed within 12 h of birth. Total placental efficiency (ratio between litter weight and total placental weight) was measured in 518 females. Variables concerning body measurements at days 42 and 90 of gestation were analyzed considering the effects of feed amount, parity order (PO) and its interaction as a 2 × 2 factorial arrangement. Body measurements at day 110 of gestation and litter traits were analyzed considering the effects of feed amounts in phase 1, feed amounts in phase 2, PO and their interactions, as a 2 × 2 × 2 factorial arrangement. As expected, BW, backfat, and caliper units were greater at days 42, 90, and 110 (P ≤ 0.006) for females fed 3.5 kg/d during the previous phase than those fed 1.8 kg. No differences were observed among feed levels in total number of piglets born, mummified fetuses, sum of born alive and stillborn piglets, and within-litter birth weight CV (P ≥ 0.118). The percentage of stillborn piglets was affected by a three-way interaction (feed level at phase 1 × feed level at phase 2 × PO). Gilts fed 1.8 kg/d at phase 1 and 3.5 kg/d at phase 2 had fewer stillborn piglets than the other females (P ≤ 0.004). Birth weight was not affected by feed levels (P ≥ 0.153); however, sows had heavier piglets than gilts (P < 0.001). Females fed 3.5 kg/d during phase 2 tended to have heavier litters (P = 0.054) than those fed 1.8 kg/d. Feeding a high level at phase 2 reduced the occurrence of lightweight piglets in gilts, but not in sows (feed level phase 2 × PO; P = 0.031). Total placental weight, average placental weight, and total placental efficiency were not affected by feed level at phase 1, feed level at phase 2 or interactions (P > 0.14). Sows had total placental weight and average placental weight greater (P ≤ 0.003) than gilts. In conclusion, increasing feed intake during phase 1, phase 2, or both phases resulted in increased maternal BW gain, without expressive effects on litter traits. Feeding 3.5 kg/d to gilts during phase 2 reduced the occurrence of lightweight piglets.

Supplemental progesterone during early pregnancy exerts divergent responses on embryonic characteristics in sows and gilts

Progesterone (P4) plays a key role in pregnancy establishment and maintenance; during early pregnancy, P4 stimulates the production and release of uterine secretions necessary for conceptus growth prior to implantation; therefore, exogenous P4 supplementation may improve embryo development. This study evaluated the effects of supplementation during early pregnancy with long-acting injectable progesterone or altrenogest on embryonic characteristics of sows and gilts. Thus, a total of 32 sows and 16 gilts were used. On day 6 of pregnancy sows and gilts were allocated to one of the following groups: non-supplemented; supplemented with 20 mg of altrenogest, orally, from days 6 to 12 of pregnancy; supplemented with 2.15 mg/kg of long-acting injectable progesterone on day 6 of pregnancy. Animals were killed on day 28 of pregnancy, and ovulation rate, embryo survival, embryo weight, crown-to-rump length, uterine glandular epithelium and endometrial vascularization were assessed. Treatments had no effect on pregnancy rate, embryo survival or endometrial vascular density (P > 0.05). Non-supplemented gilts presented larger and heavier embryos compared to gilts from supplemented groups (P < 0.05). Sows in the altrenogest group presented larger and heavier embryos compared to non-supplemented sows and sows supplemented with long-acting injectable progesterone. In conclusion, supplementation of sows and gilts with progestagen from day 6 of pregnancy can be used as a means to improve embryo survival without deleterious effects.

Investigating causal biological relationships between reproductive performance traits in high-performing gilts and sows1

Efficient management of swine production systems requires understanding of complex reproductive physiological mechanisms. Our objective in this study was to investigate potential causal biological relationships between reproductive performance traits in high-producing gilts and sows. Data originated from a nutrition experiment and consisted of 200 sows and 440 gilts arranged in body weight blocks and randomly assigned to dietary treatments during late gestation at a commercial swine farm. Reproductive performance traits consisted of weight gain during late gestation, total number born and number born alive in a litter, born alive average birth weight, wean-to-estrous interval, and total litter size born in the subsequent farrowing. Structural equation models combined with the inductive causation algorithm, both adapted to a hierarchical Bayesian framework, were employed to search for, estimate, and infer upon causal links between the traits within each parity group. Results indicated potentially distinct reproductive networks for gilts and for sows. Sows showed sparse connectivity between reproductive traits, whereas the network learned for gilts was densely interconnected, suggesting closely linked physiological mechanisms in younger females, with a potential for ripple effects throughout their productive lifecycle in response to early implementation of tailored managerial interventions. Cross-validation analyses indicated substantial network stability both for the general structure and for individual links, though results about directionality of such links were unstable in this study and will need further investigation. An assessment of relative statistical power in sows and gilts indicated that the observed network discrepancies may be partially explained on a biological basis. In summary, our results suggest distinctly heterogeneous mechanistic networks of reproductive physiology for gilts and sows, consistent with physiological differences between the groups. These findings have potential practical implications for integrated understanding and differential management of gilts and sows to enhance efficiency of swine production systems.

Recent advances in pig reproduction: Focus on impact of genetic selection for female fertility

In the past 30 years, sows have been successfully selected for a shorter weaning-to-oestrus interval and increased litter size. This review discusses the consequences of this selection for the reproductive physiology of sows, including the consequences for litter characteristics at birth. It also discusses breeding and management opportunities to deal with this changed genetics.

Genetic selection against intrauterine growth retardation in piglets: a problem at the piglet level with a solution at the sow level

Background

In polytocous livestock species, litter size and offspring weight act antagonistically; in modern pig breeds, selection for increased litter size has resulted in lower mean birth weights, an increased number of small piglets and an increased number of those affected by varying degrees of intrauterine growth retardation (IUGR). IUGR poses life-long challenges, both mental, with morphological brain changes and altered cognition, and physical, such as immaturity of organs, reduced colostrum intake and weight gain. In pigs, head morphology of newborn piglets is a good phenotypic marker for identifying such compromised piglets. Growth retardation could be considered as a property of the dam, in part due to either uterine capacity or insufficiency. A novel approach to this issue is to consider the proportion of IUGR-affected piglets in a litter as an indirect measure of uterine capacity. However, uterine capacity or sufficiency cannot be equated solely to litter size and thus is a trait difficult to measure on farm.

Results

A total of 21,159 Landrace × Large White or Landrace × White Duroc piglets (born over 52 weeks) with recorded head morphology and birth weights were followed from birth until death or weaning. At the piglet level, the estimated heritability for IUGR (as defined by head morphology) was low at 0.01 ± 0.01. Piglet direct genetic effects of birth weight (h² = 0.07 ± 0.02) were strongly negatively correlated with head morphology (− 0.93), in that IUGR-affected piglets tended to have lower birth weights. At the sow level, analysis of the proportion of IUGR-affected piglets in a litter gave a heritability of 0.20 ± 0.06, with high and negative genetic correlations of the proportion of IUGR-affected piglets with average offspring birth weight (− 0.90) and with the proportion of piglets surviving until 24 h (− 0.80).

Conclusions

This suggests that the proportion of IUGR-affected piglets in a litter is a suitable indirect measure of uterine capacity for inclusion in breeding programmes that aim at reducing IUGR in piglets and improving piglet survival.

Follicular development of sows at weaning in relation to estimated breeding value for within-litter variation in piglet birth weight

In this study we aimed to identify possible causes of within-litter variation in piglet birth weight (birth weight variation) by studying follicular development of sows at weaning in relation to their estimated breeding value (EBV) for birth weight variation. In total, 29 multiparous sows (parity 3 to 5) were selected on their EBV for birth weight variation (SD in grams; High-EBV: 15.8±1.6, N=14 and Low-EBV: -24.7±1.5, N=15). The two groups of sows had similar litter sizes (15.7 v. 16.9). Within 24 h after parturition, piglets were cross-fostered to ensure 13 suckling piglets per sow. Sows weaned 12.8±1.0 and 12.7±1.0 piglets, respectively, at days 26.1±0.2 of lactation. Blood and ovaries were collected within 2 h after weaning. The right ovary was immediately frozen to assess average follicle size and percentage healthy follicles of the 15 largest follicles. The left ovary was used to assess the percentage morphologically healthy cumulus-oocyte complexes (COCs) of the 15 largest follicles. To assess the metabolic state of the sows, body condition and the circulating metabolic markers insulin, IGF1, non-esterified fatty acid, creatinine, leptin, urea and fibroblast growth factor 21 were analysed at weaning. No significant differences were found in any of the measured follicular or metabolic parameters between High-EBV and Low-EBV. A higher weight loss during lactation was related to a lower percentage healthy COCs (β= -0.65, P=0.02). Serum creatinine, a marker for protein breakdown, was negatively related to average follicle size (β= -0.60, P=0.05). Backfat loss during lactation was related to a higher backfat thickness at parturition and to a higher average follicle size (β=0.36, P&lt;0.001) at weaning. In conclusion, we hypothesise that modern hybrid sows with more backfat at the start of lactation are able to mobilise more energy from backfat during lactation and could thereby spare protein reserves to support follicular development.

Dietary Supplementation of Leucine in Premating Diet Improves the Within-Litter Birth Weight Uniformity, Antioxidative Capability, and Immune Function of Primiparous SD Rats

The high within-litter birth weight variation has become a big issue in multiparous animals. The present study was conducted to investigate the effects of leucine supplementation in premating diet on the reproductive performance, maternal antioxidative capability, and immune function in primiparous rats. Six-week-old female SD rats were assigned to basal diet or 0.6% leucine supplemented diet for two weeks. After mating during the eighth week of age, the rats were fed with regular gestation diet. Maternal blood samples were collected on the day before mating (day −1) and day 7 and day 20 of pregnancy, while ovaries and uteruses were obtained on day −1 and on day 7, respectively. The results indicate that, compared with control group, within-litter birth weight variation was significantly decreased, while birth weights were significantly increased in the leucine group (P < 0.01). Also, leucine improved the embryo distribution uniformity and the number of implantation sites in uterine. The ovarian gene expressions of LHR, CYP19A1, and VEGFA were upregulated, while Mucin-1 was decreased significantly (P < 0.05). Leucine also increased the maternal antioxidant capacity and immune function. Conclusively, leucine supplementation in premating diet could improve the reproductive performance, which could be attributed to the improved oxidative and immune status.

Relationship Between the Estimated Breeding Values for Litter Traits at Birth and Ovarian and Embryonic Traits and Their Additive Genetic Variance in Gilts at 35 Days of Pregnancy

We investigated (1) the relationship between the estimated breeding values (EBVs) for litter traits at birth and ovulation rate (OR), average corpora luteal weight, uterine length and embryonic survival and development traits in gilts at 35 days of pregnancy by linear regression, (2) the genetic variance of OR, average corpora lutea (CL) weight, uterine length and embryonic survival and development traits at 35 days of pregnancy, and (3) the genetic correlations between these traits. Landrace (n = 86) and Yorkshire × Landrace (n = 304) gilts were inseminated and slaughtered at 35 days of pregnancy. OR was assessed by dissection of the CL on both ovaries. Individual CL was weighed and the average CL weight calculated. The number of embryos (total and vital) were counted and the vital embryos were individually weighed for calculation of within litter average and standard deviation (SD) of the embryo weight. Length of the uterine implantation site of the vital embryos was measured and the average per gilt calculated. Results suggests that increasing the EBV for total number of piglets born would proportionally increase OR and number of embryos, while decreasing the average CL weight. On the contrary, increasing the EBV for average piglet birth weight and for within litter birth weight standard deviation would increase the average CL weight. There was no relationship between the EBVs for BW and for BWSD and vital embryonic weight at 35 days of pregnancy. OR, average CL weight, number of embryos, average weight and implantation length of the vital embryos had all moderate to high heritabilities, ranging from 0.36 (±0.18) to 0.70 (±0.17). Thus, results indicate that there is ample genetic variation in OR, average CL weight and embryonic development traits. This knowledge could be used to optimize the balance between selection for litter size, average piglets birth weight and within litter birth weight uniformity.

Relationship between ovulation rate and embryonic characteristics in gilts at 35 d of pregnancy

This study investigated the relationship between ovulation rate (OR) and embryonic characteristics in gilts. Landrace ( = 86) and Yorkshire x Landrace ( = 212) gilts were inseminated with semen stored for 3 to 5 d (SS1, = 59), 6 to7 d (SS2, = 133), or 8 to 10 d (SS3, = 106), and slaughtered at 35 d of pregnancy. Ovulation rate was assessed by dissection of the corpora lutea on both ovaries. Embryos were classified as vital (VE) by visual appearance and individually weighed (VEg) and the SD of the weight calculated (SDVEg). Early embryonic mortality (EM) was estimated as the difference between OR and the number of vital plus nonvital embryos. Embryonic characteristics were analyzed with a model that included linear and quadratic terms of OR and fixed class effects of semen storage duration (SS) and genetic line (GL). Landrace gilts had a higher OR than Yorkshire x Landrace gilts (22.1 ± 0.4 vs. 20.3 ± 0.2, ≤ 0.05) and also a higher EM (6.1 ± 0.4 vs. 3.5 ± 0.3, ≤ 0.05). EM was also higher in gilts inseminated with semen stored for more than 8 d. Also, Yorkshire x Landrace gilts had a higher number of VE (16.9 ± 0.7) than the Landrace gilts (13.3 ± 0.8) when inseminations were done with semen stored for up to 5 d. Yorkshire x Landrace gilts had the highest VEg when inseminated with semen stored for 3 to 5 d (SS1: 4.9 ± 0.2 g, SS2: 4.1 ± 0.1 g, and SS3: 4.0 ± 0.2 g; ≤ 0.05). VE and VEg did not differ within Landrace gilts between different SS classes. A quadratic relationship of OR ( ≤ 0.05) was found with VE: a maximum of 16.8 VE was observed at 26 ovulations [(2.5 (± 0.6)*OR- 0.05 (± 0.01)*OR]. A quadratic relationship of OR ( ≤ 0.05) was also found for EM: a minimum of 3.33 EM was observed at 15 ovulations [(-1.1 (± 0.6)*OR -0.03 (± 0.01)*OR]. VEg was not related with OR, but SDVEg had a positive linear relationship with OR [0.01 (± 0.003)*OR, ≤ 0.05]. Results show that Yorkshire x Landrace gilts perform better than Landrace when inseminated with fresh semen, but not with semen stored for longer time. Also, the VE increases with an increase in OR up to 26, but at a lower level at higher OR, which is likely related with the increase in EM. The higher EM at higher OR might arise from a higher variation in follicular/oocyte quality leading to a higher variation in embryonic quality and development, increasing mortality before uterine implantation and the variation in embryonic weight already at 35 d of pregnancy.

Validation of transrectal ultrasonography for assessment of corpora lutea characteristics in pregnant sows and its relationship with litter characteristics at birth

In experiment 1 we investigated the accuracy of transrectal ultrasonography (TUS) to assess the number (OR) and diameter of corpora lutea (CL) in 45 and 25 sows, respectively, at 23.4 ± 2.9 d of pregnancy. The diameter was calculated as the average diameter of 10 biggest CL. Sows were subsequently slaughtered and OR was assessed by dissection of CL from both ovaries (n = 45) and average diameter of the 10 biggest CL was also calculated after measurement of CL with the caliper rule (n = 25). There was a weak relationship between OR counted after dissection of the ovaries and OR counted with TUS (β = 0.28 ± 0.01 CL/CL, P = 0.01), but there was a strong relationship between the average CL diameter measured with the caliper rule after dissection and the average CL diameter based on TUS (β = 1.0 ± 0.1 mm/mm, P < 0.0001). This shows that TUS is not a valid method to assess OR in pregnant sows but it is a valid method to assess average CL diameter. In experiment 2, we investigated the relationship between the average CL diameter assessed by TUS (n = 100) at 23.8 ± 2.4 d of pregnancy and average piglet birth weight (BW) and observed an increase of 37.6 ± 17.8 g in piglet BW per mm increase in average CL diameter measured by TUS (P = 0.04). This relationship is probably because larger CL develop from bigger follicles at ovulation, which might have ovulated oocytes of higher quality that developed into embryos with higher growth potential and thus higher birth weight.

Functional amino acids in the development of the pig placenta

The mammalian placenta is essential for supplying nutrients (e.g., amino acids and water) and oxygen from the mother to fetus and for removing fetal metabolites (e.g., ammonia and CO₂ ) from fetus to mother. Thus, placental growth and development are determinants of fetal survival, growth, and development. Indeed, low birth weight is closely associated with reduced placental growth. Providing gestating gilts or sows with dietary supplementation of arginine and glutamine, increases placental growth (including vascular growth), improves embryonic/fetal growth and survival, and reduces the large variation in birth weight among litters. These two amino acids serve as building blocks for tissue protein as well as substrates for the production of polyamines and nitric oxide, which stimulate DNA and protein synthesis and angiogenesis and vascular growth in the placenta. These recent findings not only greatly advance the field of mammalian amino acid metabolism and nutrition, but also provide practical, mechanism-based methods to enhance reproductive efficiency in swine. These results may also help improve embryonic/fetal survival and growth in other livestock species (e.g., sheep and cattle) and in humans.