This study investigated the effects of low-protein diet supplemented with Lysine (Lys), Methionine (Met), Threonine (Thr), and Tryptophan (Trp) on small intestine morphology, enzyme activity, blood urea nitrogen, and gut microbiota and metabolites in weaned piglets. Eighteen weaned pigs weighing an average of 9.57 kg received one of three treatments: a normal protein diet with 20% crude protein (CP, diet [NP]), a moderately reduced protein diet with 17% CP (MP), or a low-protein diet with 14% CP (LP). All three diets were supplemented with Lys, Met, Thr and Trp to meet essential amino acid requirements for post-weaned piglets according to the NRC (2012). Following a 45 d study period, piglets on the LP and MP diets demonstrated atrophic small intestinal morphology, with decreased villus heights and lower ratios of villus height to crypt depth (p < 0.05); pepsin activity in the stomach was also reduced in these two groups (p < 0.05). Increased plasma cholesterol and decreased blood urea nitrogen presented in the MP and LP groups compared with the NP group (p < 0.05). Overall, gastrointestinal hormones were not affected by dietary protein levels with the exception of reduced somatostatin levels in the MP and LP groups. Jejunum and colon microbiota were not affected at either the phyla or genera level in any of the diets. Colonic ammonia nitrogen concentration was reduced in MP and LP groups. Dietary protein level had no effect on short chain fatty acids or biogenic amines. Our data suggest that reducing dietary protein levels by 3% (MP) or 6% (LP) in weaned pigs has the potential to decrease nitrogen emissions and impaired digestive capacity. Therefore, dietary protein level cannot be reduced by more than 3% in consideration of maladaptive changes to small intestinal morphology and pepsin activity in weaned piglets.

Major histocompatibility complex, class II, DQ alpha 2, also named BOLA-DQA2, belongs to the Bovine Leukocyte Antigen (BOLA) class II genes which are involved in the immune response. To explore the variability of the BOLA-DQA2 gene and resistance to mastitis in cows, the splice variants (SV), targeted microRNAs (miRNAs), and single nucleotide polymorphisms (SNPs) were identified in this study. A new SV (BOLA-DQA2-SV1) lacking part of exon 3 (195 bp) and two 3′-untranslated regions (UTR) (52 bp+167 bp) of the BOLA-DQA2 gene was found in the healthy and mastitis-infected mammary gland tissues. Four of 13 new SNPs and multiple nucleotide polymorphisms resulted in amino acid changes in the protein and SNP (c. +1283 C>T) may affect the binding to the seed sequence of bta-miR-2318. Further, we detected the relative expressions of two BOLA-DQA2 transcripts and five candidated microRNAs binding to the 3′-UTR of two transcripts in the mammary gland tissues in dairy cattle by using the quantitative real-time polymerase chain reaction. The result showed that expression of the BOLA-DQA2-SV1 mRNA was significantly upregulated 2.67-fold (p<0.05) in mastitis-infected mammary tissues (n=5) compared with the healthy mammary gland mammary tissues (n=5). Except for bta-miR-1777a, miRNA expression (bta-miR-296, miR-2430, and miR-671) was upregulated 1.75 to 2.59-fold (p<0.05), whereas miR-2318 was downregulated in the mastitis cows. Our findings reveal that BOLA-DQA2-SV1 may play an important role in the mastitis resistance in dairy cattle. Whether the SNPs affect the structure of the BOLA-DQA2 gene or association with mastitis resistance is unknown and warrants further investigation.

Using protein-restriction diets becomes a potential strategy to save the dietary protein resources. However, the mechanism of low-protein diets influencing pigs’ growth performance is still controversial. This study aimed to investigate the effect of protein-restriction diets on gastrointestinal physiology and gut microbiota in pigs. Eighteen weaned piglets were randomly allocated to three groups with different dietary protein levels. After a 16-week trial, the results showed that feeding a low-protein diet to pigs impaired the epithelial morphology of duodenum and jejunum (p < 0.05) and reduced the concentration of many plasma hormones (p < 0.05), such as ghrelin, somatostatin, glucose-dependent insulin-tropic polypeptide, leptin, and gastrin. The relative abundance of Streptococcus and Lactobacillus in colon and microbiota metabolites was also decreased by extreme protein-restriction diets (p < 0.05). These findings suggested that long-term ingestion of a protein-restricted diet could impair intestinal morphology, suppress gut hormone secretion, and change the microbial community and fermentation metabolites in pigs, while the moderately low-protein diet had a minimal effect on gut function and did not impair growth performance.

Background: An increased level of the dietary protein alters the colonic microbial community and metabolic profile of pigs, but it remains unclear whether this leads to colonic inflammation and impairs barrier function in growing pigs. Results: Sixteen pigs (35.2 ± 0.3 kg) were infused with sterile saline (control) or soy protein hydrolysate (SPH) (70 g/day) through a duodenal fistula twice daily during a 15-day experimental period. The SPH treatment did not affect their average daily feed intake and daily weight gain (P > 0.05), but reduced colon index and length (P < 0.05). Illumina MiSeq sequencing revealed that species richness was increased following SPH intervention (P < 0.05). Furthermore, SPH reduced the abundance of butyrate- and propionate-producing bacteria—such as Lachnospiraceae NK4A136 group, Lachnospiraceae_uncultured, Coprococcus 3, Lachnospiraceae UCG-002, and Anaerovibrio—and increased the abundance of potentially pathogenic bacteria and protein-fermenting bacteria, such as Escherichia-Shigella, Dialister, Veillonella, Prevotella, Candidatus Saccharimonas, Erysipelotrichaceae UCG-006, Prevotellaceae_uncultured, and Prevotellaceae UCG-003 (P < 0.05). In addition, a lower content of total short-chain fatty acids, propionate, and butyrate and a higher concentration of cadaverine, putrescine, total biogenic amines, ammonia, and isovalerate were observed following SPH infusion (P < 0.05). Further analysis revealed that SPH increased the concentration of tumour necrosis factor-α, interleukin (IL)-1β, IL-6, and IL-8 in the colonic mucosa (P < 0.05). Interestingly, SPH intervention increased the expression of occludin, zonula occludens (ZO)-1, and claudin-1 in colonic mucosa (P < 0.05). Correlation analysis showed that different genera were significantly related to the production of metabolites and the concentrations of pro-inflammatory cytokines. Conclusion: An increased soy protein level in the small intestine altered the colonic microbial composition and metabolic profile, which resulted in the secretion of colonic proinflammatory cytokines and the increased expression of tight junction proteins.