Effects of high dietary zinc supplementation timing on the biological responses of gestating sows and their piglets

High dietary zinc (Zn) fed to gestating sows may have utility as a fetal
imprinting strategy to decrease pre-weaning mortality of piglets. However,
the biological action that Zn may work through is unknown. High Zn may
modulate the microbiome of the sow and the microbial seeding of the
offspring’s gut microbiome. Additonally, high dietary Zn and piglet birth
weight may alter gene expression in piglet whole blood. Sows (n = 267)
were fed 1 of 3 dietary treatments: 1) Control: a corn-soybean meal-based
diet containing 125 ppm total supplemental zinc, 2) Breed-to-Farrow: as
Control + 141 ppm supplemental Zn as ZnSO4 fed from 5 days post-breeding
to farrowing; and 3) Day 110-to-Farrow: as Control + 2,715 ppm
supplemental Zn as ZnSO4 starting on day 110 of gestation until farrowing.
A subset of third parity sows (n = 30) were selected to assess the
microbiome of colostrum, milk, and rectal and vaginal surfaces of sows. At
farrowing, 4 pigs per litter (n = 120) were selected based on birthweight
(BiW), as 2 average BiW pigs and 2 pigs with BiW below the litter average
were selected for assessing the piglet gut microbiome on the day of birth
(day 0) and day 5 of age. 16S rRNA sequencing were implemented for milk
and colostrum samples while all other sample types were sequenced using
shotgun metagenomics to determine taxonomic and functional profiles. On a
different subset of pigs, whole blood was collected from 9 LBW pigs per
treatment and 8 ABW Control pigs for RNA-sequencing to evaluate
differentially expressed genes (DEGs) and pathways. Only 2 to 3 genes were
differentially expressed between Control LBW and LBW pigs born to sows fed
high Zn. However, 262 DEGs were identified when comparing LBW and ABW
pigs, mostly reflecting pathways associated with translation, ribosome
biogenesis, and amino acid and protein synthesis. Measures of alpha
diversity (richness and Shannon’s H Index) and beta diversity
(Bray-Curtis, PERMANOVA) were conducted along with indicator species
analyses. Species with an indicator value of > 0.50 were confirmed
with a generalized linear mixed model as each P-value was corrected for
false discovery rate (FDR) to generate a Q-value. For piglet samples, the
MaAsLin2 R package was used to determine multivariate associations between
dietary treatment and piglet BiW. High dietary concentrations of Zn fed to
gestating sows did not affect the colostrum, milk, or vaginal microbial
diversity or populations of sows. Pathogenic bacteria such as Shigella
flexneri and Salmonella enterica were less abundant in fecal samples from
Breed-to-Farrow sows compared to Control sows. For piglets born to
Breed-to-Farrow sows, their gut microbiome favored fiber fermenting, short
chain fatty acid generating microbial species compared to Control pigs.
Day 110-to-Farrow piglets demonstrated a lower abundance of SCFA producing
bacteria compared to Control piglets. Gene families and pathways playing
roles in central metabolic functions (starch, pyruvate, sucrose, amino
acid metabolism) were more abundant in Breed-to-Farrow piglets compared to
pigs born to Control sows. In conclusion, high Zn fed to gestating sows
may influence SCFA-producing species and may reduce the abundance of
potential pathogenic bacteria in the sow and piglet. Piglet birth weight
may have greater effects on gene expression of neonatal pigs.