Dietary fiber (DF) supplementation during gestation has been shown to improve the reproductive performance of sows. Many studies have shown improvements in: embryo survival, litter size and weight, as well as the uniformity of piglets within the litter (Guillemet R, Hamard A, Quesnel., et. al 2007). However, most of these studies have only evaluated the inclusion effects of DF on sows’ reproductive performance, while very few have evaluated the mechanisms through which DF supplementation improves sows’ fertility.
A recent study showed that DF supplementation during gestation for three consecutive gestating periods could improve litter size and weight. As well as increasing placental weight in the second and third gestation periods (Li Y, He J, Zhang L, Liu H., et. al 2021). The placenta is an important organ for material exchange between the fetus and mother. Placenta insufficiency is a common cause that leads to low litter size, birth weight, and uniformity of piglets within litter. It is suggested that DF supplementation during gestation might improve sow reproductive performance through the improvement of placental development and function. However, it is still unclear how the DF affects placental development and function in sows.
Serotonin known as 5-hydroxytryptamine (5-HT), is mainly produced in the gut by enterochromaffin cells (ECs) and is a key neurotransmitter. It participates in the modulation of central neurotransmission and enteric physiological functions (Mawe GM., et. al, 2013), being Tryptophan its sole precursor. Within the gut, tryptophan is first converted to 5 hydroxytroptophan (5-HTP) by tryptophan hydroxylase 1 (TPH1), and is then subsequently converted into serotonin by the aromatic amino acid decarboxylase (AAAD). (O’Mahony SM, Clarke G, Borre., et. al, 2015).
Gut-derived serotonin can be transported through a serotonin transporter (SERT) to different parts of the organism, such as the placenta where it regulates various functions. Previous research studies have shown that the lack of maternal serotonin can reduce placental serotonin levels, resulting in placental insufficiency, and the inhibition of fetal growth and development (Muller CL., et. al 2017). Zhuo et al. (Zhuo Y, Cao M, Gong., et. al, 2020) demonstrated that DF supplementation could promote colonic serotonin synthesis and increase plasmatic serotonin levels in sows.
Researchers hypothesized that DF supplementation might promote placental development and function through a maternal–placental serotonin signaling pathway, which can improve fetal growth and development in gestating sows.
Figure 1. The role of dietary fiber in regulating serotonin signaling pathway and placental and fetal development in gestating sows
Source: “(Li Yang, Yang Min, Zhang Lijia., et al 2022) Frontiers in Veterinary Science.”
The study
The aim of the present study was to investigate the effects of fiber supplementation in gestation diets. Evaluating parameters such as: fetal growth, placental development and function, as well as serotonin signaling pathways, in order to explore possible mechanisms through which dietary fiber may improve sows’ reproductive performance.
Materials and Methods
A total of 16 First-Time Large White × Landrace sows were randomly assigned to two groups and fed either a semi-purified basal diet [no fiber group, 0.1% total dietary fiber] or a basal diet supplemented with 8.33 g/kg inulin and 200 g/kg cellulose [fiber group] during gestation. On the 106th day of gestation, five sows per group were chosen and sacrificed for sampling.
Results
- The results showed that dietary fiber supplementation during gestation increased total fetal weight and placental weight on day 106 of gestation; raised serum serotonin concentration; increased concentrations of serotonin and short-chain fatty acids (acetate, propionate and butyrate), as well as the expression of tryptophan hydroxylase 1, in the colon.
- It also raised serotonin and progesterone concentrations and upregulated serotonin transporter, cytochrome P450 11A1, and insulin-like growth factor 2 expressions in the placenta.
- In addition, the bristles of the fiber group had different microbial compositions compared to those of the non-fiber group.
- Fiber supplementation in the gestation diet increased the abundance of Coprococcus 3 which was positively correlated with serotonin levels within the colon. On the other hand it caused a significant reduction in the abundance of Family XIII group AD3011 which had a negative correlation with serotonin levels within the colon.
Conclusions
In conclusion, dietary fiber supplementation during gestation can increase placental serotonin levels by promoting maternal serotonin synthesis in the colon and its transport to the placenta. This improves placental development and function which will subsequently promote fetal growth.
Source: Abstract taken and modified from“Dietary Fiber Supplementation in Gestating Sow Diet Improved Fetal Growth and Placental Development and Function Through Serotonin Signaling Pathway.”