Analysis of the gut microbiota characteristics of sows during reproductive cycle

To explore the succession and structural characteristics of intestinal flora of sows during the reproductive cycle, twelve Large White sows were selected as the study objects from a pig farm in Laixi, Shandong Province. Fresh fecal samples were collected from 11 time points in 5 stages of the reproductive cycle, including the non-pregnancy period（2 days before mating）, the pre-gestation period（28, 42 and 56 days after mating）, the late gestation period（70, 84 and 98 days after mating）, the farrowing period（the day of delivery） and the lactation period（7, 14 and 21 days after parturition）. The genomic DNA was extracted from the samples. Subsequently, high-throughput sequencing technology targeting the 16S rRNA gene was employed to examine the gut microbial diversity and the microbial composition and structure characteristics at the phylum, family, and genus levels at different stages of Large White sow reproductive cycles. The results showed as follows: the α-diversity of gut microorganisms was the lowest at the non-pregnancy period during the reproductive cycle of Large White sows; it gradually increased with the progress of pregnancy; recorded the highest at the late gestation period, and sharply decreased after the farrowing period, and there was no significant difference between the lactation period and the farrowing period（P＞0.05）. The average number of species at the five stages ranged from 400 to 800, and the number of species in the late gestation period was the largest, and the difference between the number of species at the other stages was significant or extremely significant（P＜0.05 or P＜0.001）,except that there was no significant difference in the number of species between the non-pregnancy stage and the pre-pregnancy stage（P＞0.05）. There were variations in β-diversity during different stages of the reproductive cycle（P=0.001）. The similarity of β-diversity was the highest between non-pregnancy and pre-pregnancy, which was higher between parturition and lactation, and that was the largest between non-pregnancy and late gestation periods. During the reproductive cycle of sows, their intestinal flora was composed of 32 phyla, 283 families, and 633 genera. The top ten phyla with the highest relative abundance were Firmicutes, Bacteroidota, Actinobacteriota, Proteobacteria, Spirochaetota, Cyanobacteria, Synergistota, Verrucomicrobiota, Campilobacterota, and Acidobacteriota. Among them, Firmicutes and Bacteroides were the dominant phyla, and the ratio of the two was the highest during the farrowing period and lowest during the non-pregnancy period. A total of 29 families with a relative abundance greater than 1% were annotated, among which the dominant families were Clostridiaceae, Peptostreptococcaceae, and Oscillospiraceae. The dominant bacterial families in the late pregnancy period and the farrowing period also include Muribaculaceae. A total of 47 notable genera were detected（LDA＞2.0）, among which 9 characteristic bacteria genera existed in the non-pregnancy period, the relative abundance of which was Clostridium＿sensu＿stricto＿1. In the pre-pregnancy period, 8 notable genera were observed, the relative abundance of which was Christensenellaceae＿R＿7＿group; 13 characteristic genera were present during the late gestation period, the relative abundance of which was Clostridia＿UCG＿014 and Prevotellaceae＿NK3B31＿group; 7 characteristic genera were present during the farrowing period, the relative abundance of which was Muribaculaceae; and 11 characteristic genera were present during lactation, the relative abundance of which was Bacteroides. These findings suggested that there were differences in intestinal flora diversity at different stages of the reproductive cycle of Large White sows, and each stage had its own characteristic genera.