Correlates of reproductive tract anatomy and uterine histomorphometrics with fertility in swine

Exploring Hyperprolific Sows: A Study of Gross Morphology of Reproductive Organs and Oxytocin Receptor Distribution across Parities

This study investigated the gross morphology of reproductive organs and oxytocin receptor distribution across different parities in hyperprolific sows. A total of thirty-two reproductive organs from Landrace × Yorkshire crossbred sows were categorized into three groups based on parity numbers: 1 (n = 10), 2-5 (n = 12), and ≥6 (n = 10). All sows were culled due to management problems, and none had reproductive disorders. A gross morphology examination of the ovaries, uterus, and the rest of the reproductive tract was conducted. Using immunohistochemistry, the levels of oxytocin receptor were evaluated in five layers of the uterus, the epithelial, superficial glandular, deep glandular, and circular and longitudinal smooth muscles of the myometrium, and were quantified using an H-score. On average, the age and body weight of sows and the total number of piglets born per litter were 799.8 ± 327.8 days, 213.2 ± 31.7 kg, and 15.5 ± 4.8, respectively. The numbers of ovulations in sows in parity number 1 (19.9 ± 2.4) were lower than those in sows in parity numbers 2-5 (29.7 ± 2.0, p = 0.004) and ≥6 (27.7 ± 2.1, p = 0.022). The uterine weights of sows in parity number 1 (902.9 ± 112.5 g) were lower than those of parity numbers 2-5 (1442.1 ± 111.8 g, p = 0.001) and ≥6 (1394.3 ± 125.1 g, p = 0.004). The length of the uterus in sows with parity number 1 (277.9 ± 26.1 cm) was shorter than those in sows with parity numbers 2-5 (354.6 ± 25.9 cm, p = 0.033) and tended to be shorter than those in sows with parity numbers ≥ 6 (346.6 ± 29.0 cm, p = 0.068). The immunolocalization of oxytocin receptors could be detected in various parts of the porcine endometrium and myometrium. Among the five tissue layers of the uterus, the H-score of oxytocin receptors in the deep uterine glands was greater than in the superficial uterine glands (p = 0.023) and the circular muscle layer of the myometrium (p = 0.011), but it did not differ from the epithelial layer of the endometrium (p = 0.428) or the longitudinal muscle layer of the myometrium (p = 0.081). Sows with parity numbers ≥ 6 had a lower oxytocin receptor H-score than those with parity numbers 1 (p < 0.001) and 2-5 (p < 0.001). In conclusion, these data emphasize the notable variations in several reproductive parameters and the levels of oxytocin receptor within the uterus of hyperprolific sows. Across the majority of uterine tissue layers, there was a marked decrease in the H-score of the oxytocin receptor in the older sows.

Identification and characterization of circRNAs in peri-implantation endometrium between Yorkshire and Erhualian pigs

BACKGROUND

One of the most critical periods for the loss of pig embryos is the 12th day of gestation when implantation begins. Recent studies have shown that non-coding RNAs (ncRNAs) play important regulatory roles during pregnancy. Circular RNAs (circRNAs) are a kind of ubiquitously expressed ncRNAs that can directly regulate the binding proteins or regulate the expression of target genes by adsorbing micro RNAs (miRNA).

RESULTS

We used the Illumina Novaseq6,000 technology to analyze the circRNA expression profile in the endometrium of three Erhualian (EH12) and three Yorkshire (YK12) pigs on day 12 of gestation. Overall, a total of 22,108 circRNAs were identified. Of these, 4051 circRNAs were specific to EH12 and 5889 circRNAs were specific to YK12, indicating a high level of breed specificity. Further analysis showed that there were 641 significant differentially expressed circRNAs (SDEcircRNAs) in EH12 compared with YK12 (FDR < 0.05). Functional enrichment of differential circRNA host genes revealed many pathways and genes associated with reproduction and regulation of embryo development. Network analysis of circRNA-miRNA interactions further supported the idea that circRNAs act as sponges for miRNAs to regulate gene expression. The prediction of differential circRNA binding proteins further explored the potential regulatory pathways of circRNAs. Analysis of SDEcircRNAs suggested a possible reason for the difference in embryo survival between the two breeds at the peri-implantation stage.

CONCLUSIONS

Together, these data suggest that circRNAs are abundantly expressed in the endometrium during the peri-implantation period in pigs and are important regulators of related genes. The results of this study will help to further understand the differences in molecular pathways between the two breeds during the critical implantation period of pregnancy, and will help to provide insight into the molecular mechanisms that contribute to the establishment of pregnancy and embryo loss in pigs.

Short-term consumption of the mycotoxin zearalenone by pubertal gilts causes persistent changes in the histoarchitecture of reproductive tissues

Consumption of zearalenone (ZEN) detrimentally affects tissues and systems throughout the body, and these deleterious effects are especially pronounced in swine. The objectives of this project were to determine the effects of short-term consumption of ZEN (at concentrations that could be found on-farm) on growth, carcass weight, liver weight, and reproductive tissues of pubertal gilts, and to determine if the effects are transient or persistent. Cross-bred gilts (107.25 ± 2.69 kg) were randomly assigned to one of three feed treatments: 1) solvent only for 21 d (CON; n = 10), 2) ZEN for 7 d followed by 14 d of solvent (ZEN-7; 6 mg/d; n = 10), and 3) ZEN for 21 d (ZEN-21; 6 mg/d; n = 10). Body weights were collected at the beginning and end of the experiment (189.1 ± 0.8 and 211.1 ± 0.8 d of age, respectively). Carcass weights and tissues were collected at harvest. There were no treatment-based differences in growth, carcass, liver, or reproductive tissue weights. Histological analyses revealed differences based on treatment and the interaction between treatment and luteal status. The thickness of the ampullary muscularis declined with ZEN exposure (P < 0.05), while the isthmic epithelial cell height (P < 0.01) and uterine endometrial thickness (P < 0.02) increased. Interestingly, the thickness of the isthmic muscularis, uterine myometrium, and epithelial cell height only differed in the presence of a corpus luteum. Uterine epithelial cell height in the luteal phase was lowest in ZEN-7 pigs (P < 0.01). The isthmic muscularis in the luteal phase was thinner in pigs from both ZEN treatments (P < 0.01). Conversely, the luteal-stage myometrium was thicker in pigs from both ZEN treatments (P < 0.01). The discovery of these tissue-based differences during the luteal phase is particularly concerning since this corresponds with the time when embryos would be affected by the functional competency of the oviduct and uterus. The results of this work demonstrate that short-term consumption of ZEN produces microscopic, but not macroscopic alterations in reproductive organs which are likely to have negative effects on their subsequent function and that these differences persist even after ZEN consumption ceases. Taken together, these results indicate that it is insufficient to rely solely on outwardly visible symptoms as indicators of zearalenone exposure, as detrimental effects on reproductive tissues were found in the absence of phenotypic and morphologic changes.

The roles and expression of HOXA/Hoxa10 gene: A prospective marker of mammalian female fertility?

This review addresses the influence of homebox A10/a10 (HOXA/Hoxa10) gene on reproductive tract anatomy and functional fertility in mammalian species, and discusses major endocrine and environmental regulators of HOXA/Hoxa10 expression. Female reproductive efficiency or success is a function of several factors including the ovulation and fertilization rate, and uterine receptivity. A family of HOX/Hox genes establishes the segmental identity of the reproductive tract during embryogenesis and retains its physiological plasticity in sexually mature animals and humans. In particular, the HOXA/Hoxa10 gene is an intrinsic component of implantation, decidualization, and immunomodulation in the adult uterus. It was, therefore, suggested that knowledge of HOXA/Hoxa10 regulation might be essential in navigating molecular mechanisms with the aim of enhancing female reproductive potential. However, a recent study in pigs revealed a lack of associations between endometrial HOXA10 expression and reproductive tract morphology, and very poor correlations with sows' fertility metrics. Retinoic acid mainly regulates 3' HOX/Hox paralogs but may also modify the expression of downstream HOX/Hox genes, including HOXA/Hoxa10. Sex steroids directly regulate HOXA/Hoxa10 expression. The vitamin D receptor pathway modulates HOXA/Hoxa10 expression in the adult reproductive tract. Lastly, endocrine disruptors such as diethylstilbestrol, methoxychlor, bisphenol A, and isoflavones were shown to alter HOXA/Hoxa10 expression, thus affecting reproductive competence of the female.

Atypical for northern ungulates, energy metabolism is lowest during summer in female wild boars (Sus scrofa)

Typically, large ungulates show a single seasonal peak of heart rate, a proxy of energy expenditure, in early summer. Different to other large ungulates, wild boar females had peak heart rates early in the year (at ~ April, 1), which likely indicates high costs of reproduction. This peak was followed by a trough over summer and a secondary summit in autumn/early winter, which coincided with the mast seeding of oak trees and the mating season. Wild boars counteracted the effects of cold temperatures by decreasing subcutaneous body temperature by peripheral vasoconstriction. They also passively gained solar radiation energy by basking in the sun. However, the shape of the seasonal rhythm in HR indicates that it was apparently not primarily caused by thermoregulatory costs but by the costs of reproduction. Wild boar farrow early in the year, visible in high HRs and sudden changes in intraperitoneal body temperature of females. Arguably, a prerequisite for this early reproduction as well as for high energy metabolism over winter is the broad variety of food consumed by this species, i.e., the omnivorous lifestyle. Extremely warm and dry summers, as experienced during the study years (2017, 2018), may increasingly become a bottleneck for food intake of wild boar.