The results of the study are discussed separately regarding the prenatal and postnatal effects.
Prenatal effects of BPC on sows and their offspring
Hyperprolific dam-line sows have high quantity of foetuses in utero with increasing nutritional requirements, especially during the last third term of gestation. To support the requirements of the growing foetus, placental size and exchange surface area requires to be increased. Such adaptations contribute to optimize nutrient availability during late gestation and improve foetal growth and survival [23]. Thus, conditions regarding placental vascularization are critical for the intrauterine function, and deficiencies may result in reduced BW of piglets born alive and poor survival especially during the periparturient period[2]. In this context, two biological processes are related with tissue neovascularization. While vasculogenesis occurs during embryo development, resulting in the de novo formation of blood vessels by the accumulation of angioblasts (endothelial precursors), angiogenesis is involved in tissue growth and regeneration, by extension of vasculature formed from vasculogenesis [24].
According to Rajasekar et al. [20] several dietary natural compounds (e.g. polyphenols, terpenoids and plant extracts) have been associated to potential modes of action of modulating angiogenesis pathways. In general, they may modulate angiogenesis by down-regulating the secretion of angiogenesis factors such as VEGF, FGF, Ang, MMPs, or by inhibiting receptor mediated signalling pathways (PI3K/Akt, ERK) involved in hypoxic and inflammatory conditions. An effect of BPC on placental neovascularization might be associated to alterations (imbalance) between pro- and anti-angiogenic factors [20].
Recent studies have shown the transfer of PC such as anethole, cinnamaldehyde, eugenol [25], limonene and carvone [15] from the feed to amniotic fluid of sows during gestation, with effects on reproductive performance and mammary secretions [14], as well as, the antioxidant status in gestating sows [26]. The results of the present study are in line with such findings with the relative increase of BPC limonene, anethole, borneol, p-cymene, and eucalyptol in the sow’s amniotic fluid compared to the Control group. It was previously reported that prenatal exposure of foetus to specific BPC containing eucalyptol, p-cymene, linalool, anethole, and thymol essential oils along the gestation period increased the litter size (born alive) [14]. This may reflect improvements on reproductive parameters as the ovulation rate, embryonic survival, and/or uterine and placenta function [1].
The modes of action on tendencies observed in this study regarding the reproductive performance suggest an influence of the supplemented BPC on placental functionality, however, remains unclear. Possibly the observed effect on the sows’ oxidative status is related to this effect. A potential of improving the antioxidant status of sows with BPC was shown already by Meng et al. [27] where dietary resveratrol (polyphenol) supplementation during gestation, increased both the CAT and GSH-Px plasma levels by modulation of the Keap1-Nrf2 pathway and Sirt1 in the placenta. In the present study, it was shown that BPC sows had higher plasma TBARS levels and CAT activity, but lower SOD levels during the early period of gestation (d 35). The changes could indicate an antioxidant response (acquisition of tolerance) to protect cell from endogenous free radical attacks [28].
Upon birth, a critical factor for further development of the new-born piglets is their colostrum intake. Quesnel and Farmer [29] describe that sow nutrition during late gestation may influence colostrogenesis, which starts approximately 10 days before farrowing, englobing both, the synthesis of milk-specific constituents and the transfer of IgG into lacteal secretions. During colostrogenesis, tight junctions between mammary epithelial cells are leaky, thereby allowing paracellular transfer of constituents from maternal plasma to the alveolar compartment, especially hormones, growth factors and Ig. It is noteworthy that colostrum protein content in the BPC group was increased. Therefore, it would be of high interest for further studies to investigate the proportion of different compounds within the protein fraction of the colostrum in BPC supplemented sows. An increased amount of growth factors and immunoglobulins could offer an advantage for piglets in their early-life development, especially until their own immune system is fully functional.
Dietary phytochemicals have been shown to offer a potential for modulating a range of biological process and pathways (e.g. nutrient transport, immune and inflammatory response, and muscle physiology and metabolism) with transcriptome profiles in human adults [30], pigs [31], and poultry [32]. The gene expression analysis performed in the present study on the jejunum of new-born piglets showed that supplementation of BPC to gestating sows up-regulated mRNA levels of SLC11A2, SLC16A1, SLC39A4, and ALPI genes, which are related to gut function in neonate piglets. Specifically, the solute carrier family gene SLC11A2 is involved in intestinal uptake of divalent metals, especially Fe2+ [33], SLC16A1 plays a role in the luminal absorption of short-chain fatty acids [34], SLC39A4 is required for intestinal uptake of zinc [35], while ALPI is enterocyte differentiation dependent involved in phosphate digestion and fat absorption, as well as detoxification of pathogenic bacterial [36]. Upregulation of these genes suggests a potential improvement on the capacity for intestinal nutrient uptake and transport. Likewise, the observed upregulation of the SOD gene suggests an effect on the antioxidant system [37]. The IFN-γ gene was downregulation in the BPC compared to the Control group, and this may be positively related to the innate immune response [34], as auto-regulatory loop of local inflammation [38].
To our knowledge, there are no studies in swine reporting on effects of the prenatal maternal transfer of PC on the neonatal programming regarding parameters for the intestinal integrity. The term ‘gut health’ encompasses a number of physiological and functional mechanisms including morphological, anatomical, microbial, enzymatic and immunological, and the interactions between these components [39]. In particular, atrophied villus structure and hyperplasia indicated by a decreased VH and increased CD [40], as well as, dysfunctionality of specialized epithelial cell types such as goblet cells [11] are compatible with an impaired of the mucosa (epithelium) GIT. It was demonstrated that IUGR conditions affected weight and structure (villous size) of the intestine and enhanced counts of adherent bacteria to the epithelium [8]. In this study, new-born piglets in the BPC supplemented group showed higher VH, ratio of VH:CD, and goblet cell density when compared with new-born piglets from the Control group, indicating that BPC would act in opposition to IUGR intestinal impairs.
Taking together the observed response on gene expression, intestinal histomorphology, nutrient transporters, oxidative status, and immune parameters by supplementation of BPC group suggest prenatal programming of some biological mechanisms involved in the development of the foetus until birth. Considering the direction of differences, although intrauterine space is not modified resulting in lower and less uniform new-born piglet BW, BPC supplementation to the sow´s gestation diet could have increased supply of total nutrients, resulting in improved perinatal survival.
Postnatal effects of BPC supplementation on sows and piglets
The analysis of volatile compounds in milk at day 20 of lactation showed differences in the transfer of specific BPC. Relative concentrations of limonene, anethole, and p-cymene were increased in milk of BPC supplemented sows. However, no evidence for increased milk concentrations of eucalyptol and borneol were found in the BPC group in contrast to findings from placental liquid. Potentially these differences could be related to the bioavailability and chemical structure of the analysed BPC (e.g., molecular weight, size, lipophilicity, hydrophilicity, and charge) [41]. This has an especial interest because Kirsch and Buettner [42] reported a carry-over of eucalyptol into human milk. Song et al. [43] mentioned that differences in the relative concentrations of phytochemicals such as flavonoids and carotenoids in human milk may be a result of several factors, including dietary exposure, stability in the milk matrix, efficiency of absorption/metabolism, and transfer from plasma to milk.
Regarding possible effects of the BPC present in the maternal diet, it was previously reported that they can have an influence on nutritional programming and/or sensory conditioning and further performance during the perinatal period. For example, a study by Val-Laillet et al. [13] used two different blends of PC (limonene and cinnamaldehyde, or menthol, carvone, and anethole) as sensory feed additives in gestating and lactating sows. These supplemented PC were detected in both colostrum and milk of the sows and suckling pigs that were exposed to feed additives via the maternal diet showed improved ADG and ADFI compared to piglets from sows without supplementation of PC. This type of perinatal exposure to PC could influence nutritional programming and/or sensory conditioning during an important time for the development of flavour preferences, appetite regulation, and nutritional programming, both in humans and pigs [44].
In the present study, lactating sows receiving the BPC tended to have increased ADFI and their offspring showed higher BWG from birth to weaning than piglets from sows receiving the Control. Similar to these findings, Tan et al. [45] described a tendency to increase the feed intake of lactating sows after dietary supplementation of 15 mg/kg oregano EO, with improved piglets ADG from birth to day 21 of lactation. In addition, Wang et al. [46] reported an improved ADFI and milk yield during lactation and in addition the body weight of piglets at weaning was increased with dietary supplementation of 0.5% of star anise during gestation and lactation of sows. They indicated that star anise in diet improved the lactation performance of sows by increasing concentrations of insulin-like growth factor-1 in milk and prolactin in serum of sows.
These effects may be linked not only to feed intake of the animals, but also their oxidative status. As catabolic conditions during late gestation and lactation increase the production of reactive oxygen species it is well accepted that hyperprolific sows may be under systemic oxidative stress [47], [45]. This can affect not only fertility and well-being of sows, but also their piglets’ [48], as oxidative factors can be transferred to the offspring through mammary secretions [49]. Therefore, dietary programs reducing oxidative stress in sows are of interest. A potential of PC in this regard was shown for example by the previously cited study of Tan et al. [45] where supplementation of 15 mg/kg oregano EO during gestating and lactating resulted in reduced TBARS serum levels in sows on early lactation when compared with early gestation levels. In addition, evidence has shown that dietary supplementation with certain botanical functional substances; alleviate oxidative stress in sows and their offspring. For example, Meng et al. [27] described a positive effect of dietary supplementation of resveratrol, a plant phenol, during lactation, which affords protection against inflammation and oxidative stress, improving the SOD and CAT levels in both plasma and milk of sows and piglets. A similar result was obtained in the present study by the BPC supplementation during lactation, with an increase in both CAT and SOD plasma levels of the lactating sows and their piglets.
Especially targeting the endogenous antioxidant response of animals might be promising target to increase resilience against oxidative stress. Particularly SOD and CAT are interesting enzymes in this regard, as SOD acts as a primary defence against superoxide anion radical and converting it to H2O2, while CAT, a haem-containing enzyme, in turn detoxifies H2O2 to water and non-ROS, protecting the tissues from high peroxide levels [50]. Studies in rodents demonstrated the potential of oral treatment with D-limonene to increase the activities of both SOD and CAT, reducing the oxidative stress in diabetic rats by decreasing lipid peroxidation [51]. Similar results were obtained by De Oliveira et al. [52] after dietary supplementation of p-cymene in mice. The level of lipid peroxidation and nitrite content was reduced while CAT and SOD activities increased. These findings suggest that the antioxidant effect of these BPC (containing limonene and p-cymene) may be due to positive modulation of the activity of these antioxidant enzymes.
the overall metabolism, physiology, disease status and performance of young piglets,an optimally functioning gastrointestinal tract the gene expression analysis of jejunum samples from suckling piglets showed that BPC supplementation in lactating sows resulted in an upregulation of some genes related to gut barrier function (MUC, CLDN4, CLDN15, TFF3) which could act as possible markers for gut barrier functionBriefly, MUC is related to intestinal secretion of gel-forming mucin [54], CLDN4 and CLDN15 involved in the transmembrane protein sealing functions, and mucosal differentiation, respectively [55], as well as, TFF3 functioning as mucosal protection and epithelial restitution [54]. In further studies it would be interesting to study if these effects on intestinal barrier genes together with the observed histomorphological changes in the jejunum of piglets from the BPC fed sows are related to the observed improvement of BW gain from birth to weaning.