Metabolic and Proteomic Responses to Long-Term Protein Restriction in a Pig Model

Low crude protein formulation with supplemental amino acids for its impacts on intestinal health and growth performance of growing-finishing pigs

BACKGROUND

Low crude protein (CP) formulations with supplemental amino acids (AA) are used to enhance intestinal health, reduce costs, minimize environmental impact, and maintain growth performance of pigs. However, extensive reduction of dietary CP can compromise growth performance due to limited synthesis of non-essential AA and limited availability of bioactive compounds from protein supplements even when AA requirements are met. Moreover, implementing a low CP formulation can increase the net energy (NE) content in feeds causing excessive fat deposition. Additional supplementation of functional AA, coupled with low CP formulation could further enhance intestinal health and glucose metabolism, improving nitrogen utilization, and growth performance. Three experiments were conducted to evaluate the effects of low CP formulations with supplemental AA on the intestinal health and growth performance of growing-finishing pigs.

METHODS

In Exp. 1, 90 pigs (19.7 ± 1.1 kg, 45 barrows and 45 gilts) were assigned to 3 treatments: CON (18.0% CP, supplementing Lys, Met, and Thr), LCP (16.0% CP, supplementing Lys, Met, Thr, Trp, and Val), and LCPT (16.1% CP, LCP + 0.05% SID Trp). In Exp. 2, 72 pigs (34.2 ± 4.2 kg BW) were assigned to 3 treatments: CON (17.7% CP, meeting the requirements of Lys, Met, Thr, and Trp); LCP (15.0% CP, meeting Lys, Thr, Trp, Met, Val, Ile, and Phe); and VLCP (12.8% CP, meeting Lys, Thr, Trp, Met, Val, Ile, Phe, His, and Leu). In Exp. 3, 72 pigs (54.1 ± 5.9 kg BW) were assigned to 3 treatments and fed experimental diets for 3 phases (grower 2, finishing 1, and finishing 2). Treatments were CON (18.0%, 13.8%, 12.7% CP for 3 phases; meeting Lys, Met, Thr, and Trp); LCP (13.5%, 11.4%, 10.4% CP for 3 phases; meeting Lys, Thr, Trp, Met, Val, Ile, and Phe); and LCPG (14.1%, 12.8%, 11.1% CP for 3 phases; LCP + Glu to match SID Glu with CON). All diets had 2.6 Mcal/kg NE.

RESULTS

In Exp. 1, overall, the growth performance did not differ among treatments. The LCPT increased (P < 0.05) Claudin-1 expression in the duodenum and jejunum. The LCP and LCPT increased (P < 0.05) CAT-1, 4F2hc, and B0AT expressions in the jejunum. In Exp. 2, overall, the VLCP reduced (P < 0.05) G:F and BUN. The LCP and VLCP increased (P < 0.05) the backfat thickness (BFT). In Exp. 3, overall, growth performance and BFT did not differ among treatments. The LCPG reduced (P < 0.05) BUN, whereas increased the insulin in plasma. The LCP and LCPG reduced (P < 0.05) the abundance of Streptococcaceae, whereas the LCP reduced (P < 0.05) Erysipelotrichaceae, and the alpha diversity.

CONCLUSIONS

When implementing low CP formulation, CP can be reduced by supplementation of Lys, Thr, Met, Trp, Val, and Ile without affecting the growth performance of growing-finishing pigs when NE is adjusted to avoid increased fat deposition. Supplementation of Trp above the requirement or supplementation of Glu in low CP formulation seems to benefit intestinal health as well as improved nitrogen utilization and glucose metabolism.

Advances, Implications, and Limitations of Low-Crude-Protein Diets in Pig Production

Currently, five crystalline essential amino acids (Lys, Met, Thr, Trp, and Val) are generally used, allowing formulation of low-crude-protein (CP) diets. Moreover, Ile may also be used depending on its economic value and the specific feeding program. Experimentally, it has been shown that further reduced CP levels can be achieved by supplemental His, Leu, and Phe to the diets. However, decreasing the dietary CP level while maintaining optimal ratios of amino acids has shown contradictory effects on pigs' growth performance. Due to the divergence in the literature and the importance for practical formulation strategies in the swine industry, a literature review and a meta-analysis were performed to estimate the minimum CP level that would not compromise pig performance. Based on the present review, there is a minimum CP level after which the growth performance of pigs can be compromised, even though diets are balanced for essential amino acids. Considering average daily gain and gain to feed, respectively, these levels were estimated to be 18.4% CP (95% confidence interval [CI]: 16.3 to 18.4) and 18.3% CP (95% CI: 17.4 to 19.2) for nursery, 16.1% CP (95% CI: 16.0 to 16.2) and 16.3% CP (95% CI: 14.5 to 18.0) for growing, and 11.6% CP (95% CI: 10.8 to 12.3) and 11.4% CP (95% CI: 10.3 to 12.5) for finishing pigs.

Impact of dietary Chlorella vulgaris and feed enzymes on health status, immune response and liver metabolites in weaned piglets

In this study, we analysed the impact of dietary inclusion of Chlorella vulgaris and carbohydrases on general health, redox status, immune response, liver lipids and metabolites in weaned piglets. Forty-four male piglets were allocated into four diets: control (n = 11), CH (control diet with 5% CH, n = 10), CH+R (control diet with 5% CH plus 0.005% Rovabio Excel AP, n = 10), and CH+M (control diet with 5% CH plus 0.01% of a pre-selected four-CAZyme mixture, n = 11). After 15 days of trial, animals were slaughtered and samples of blood and liver collected. Spectrophotometry methods and commercial kits were used to determine blood parameters and gas and liquid chromatography for hepatic fatty acid and chlorophylls profiles, respectively. While total, LDL- and VLDL-cholesterol were increased by CH, the opposite was recorded for HDL-cholesterol (p < 0.001). Piglets fed CH-based diets presented an increase of IgG and a decrease of IgM (p < 0.001) which along with lymphocytes exacerbation contributed for piglets' survival after weaning. n-6 PUFA were reduced in piglets fed CH and the opposite occurred for n-3 PUFA (p < 0.001), thus benefiting n-6/n-3 ratio in the liver. Chlorophylls amount was not changed by the use of Rovabio or enzymatic mixture. The discriminant analysis applied to hepatic parameters revealed a clear separation between control and CH-based diets but failed to discriminate feed enzymes. Our findings indicate health promoting effects of CH as feed ingredient in piglets' nutrition at weaning, without negatively impacting on animals' performance.

Effects of early sub-therapeutic antibiotic administration on body tissue deposition, gut microbiota and metabolite profiles of weaned piglets

BACKGROUND

This study aimed to evaluate the effects of sub-therapeutic antibiotic (STA) administration and its subsequent withdrawal on the body tissue deposition, gut microbiota, and metabolite profiles of piglets. The piglets in the experimental group were fed with STA (30 mg kg^-1 bacitracin methylene disalicylate, 75 mg kg^-1 chlortetracycline, 300 mg kg^-1 calcium oxytetracycline) for 14 days and the target bodyweight of the withdrawal period was 25 kg.

RESULTS

The experiment was divided into two periods: the administration period and the withdrawal period. The results showed that STA did not improve piglets' growth performance during the two periods. Piglets treated with STA had lower body water deposition during the withdrawal period and tended to increase body lipid deposition during the withdrawal period and the whole period in comparison with the piglets in the control group. It was found that STA markedly altered the colonic microbiota and their metabolites in the piglets. Sub-therapeutic antibiotics were initially effective in decreasing the abundance of pathogenic bacteria during the administration period; however, STA could not continue the effect during the withdrawal period, leading to a rebound of pathogenic bacteria such as Alloprevotella and the increased abundance of other pathogenic bacteria like Oscillibacter. Remarkably, STA treatment decreased Blautia abundance. This bacterium plays a potential protective role against obesity. Metabolomic analysis indicated that STA mainly altered amino acid metabolism, lipid metabolism, and carbohydrate metabolism during the two periods. Spearman's correlation analysis showed that the gut microbiota was highly correlated with microbial metabolite changes.

CONCLUSION

These results suggest that early STA administration may alter body tissue deposition later in life by reshaping the gut microbiota and their metabolite profiles. © 2022 Society of Chemical Industry.

A Novel Method for Constructing Classification Models by Combining Different Biomarker Patterns

Different biomarker patterns, such as those of molecular biomarkers and ratio biomarkers, have their own merits in clinical applications. In this study, a novel machine learning method used in biomedical data analysis for constructing classification models by combining different biomarker patterns (CDBP)is proposed. CDBP uses relative expression reversals to measure the discriminative ability of different biomarker patterns, and selects the pattern with the higher score for classifier construction. The decision boundary of CDBP can be characterized in simple and biologically meaningful manners. The CDBP method was compared with eight state-of-the-art methods on eight gene expression datasets to test its performance. CDBP, with fewer features or ratio features, had the highest classification performance. Subsequently, CDBP was employed to extract crucial diagnostic information from a rat hepatocarcinogenesis metabolomics dataset. The potential biomarkers selected by CDBP provided better classification of hepatocellular carcinoma (HCC)and non-HCC stages than previous works in the animal model. The statistical analyses of these potential biomarkers in an independent human dataset confirmed their discriminative abilities of different liver diseases. These experimental results highlight the potential of CDBP for biomarker identification from high-dimensional biomedical datasets and demonstrate that it can be a useful tool for disease classification.

Effects of Dietary Protein Levels on Fecal Amino Acids Excretion and Apparent Digestibility, and Fecal and Ileal Microbial Amino Acids Composition in Weaned Piglets

Background and Aims: The purpose of this study was to determine the effects of low protein diets with the same Lys, Met + Cys, Thr, and Trp levels as in high protein diets on the fecal amino acid excretion and apparent digestibility, and ileal and fecal microbial amino acids composition in weaned piglets.

Methods: Fifty-four 21-day-old Duroc × Landrace × Yorkshire weaned piglets were randomly divided into three groups and fed with corn-soybean meal basal diets, in which the crude protein (CP) content was 20% (H-CP), 17% (M-CP), and 14% (L-CP), respectively. The experiment included a 7-day adaptation period and a 45-day trial period. Six piglets in each group were randomly slaughtered on days 10, 25, and 45 of the trial period, and the intestinal contents, intestinal mucosa, and feces were collected.

Results: The results showed that the interaction between feeding time and dietary CP levels was reflected in the apparent digestibility of dietary CP and amino acid (AA) (p < 0.01). With the increase of age, the apparent digestibility of CP and AA were increased (p < 0.01). With the increase of CP levels, the excretion of nitrogen (N) was decreased (p < 0.01), whereas the flow of microbial AA in the ileum and feces were increased (p < 0.01). The interaction between feeding time and dietary CP levels was also reflected in the composition of AA in the ileum and stool of piglets (p < 0.01). The proportion of His, Lyr, Met, Cys, and Ser was lower than the average, whereas the proportion of Phe, Leu, Pro, Ala, Glu, and Asp was higher than the average. With the increase of age, the AA content of microorganisms increased (p < 0.01).

Conclusion: All in all, this work revealed the changes of N, CP, and AA excretion and digestibility of feces and microorganisms of piglets under the combined action of different dietary protein levels and different feeding times, and also the changes of AA composition of intestinal microorganisms and AA composition of microorganisms.

Alterations and Correlations of the Gut Microbiome, Performance, Egg Quality, and Serum Biochemical Indexes in Laying Hens with Low-Protein Amino Acid-Deficient Diets

The present study was carried out to investigate the effects of methionine (Met), lysine (Lys), isoleucine (Ile), and threonine (Thr) deficiency in a low-protein diet on laying performance, egg quality, serum biochemical indices, and the gut microbiota in laying hens. A total of 300 Peking Pink laying hens, at 38 weeks of age, were randomly allocated to five dietary treatments, each of which included six replicates of ten hens. Hens were fed an amino acid-balanced diet (Met: 0.46%; Lys: 0.76%; Ile: 0.72%; Thr: 0.56%; positive control, PC), Met deficiency diet (Met-, 0.25%), Lys deficiency diet (Lys-, 0.56%), Ile deficiency diet (Ile-, 0.54%), and Thr deficiency diet (Thr-, 0.46%) for 12 weeks. Hens were housed in pairs in 45 × 45 × 45 cm wire cages with three ladders and three birds per cage. Feed and water were provided ad libitum during the entire experimental period. All data were analyzed using one-way ANOVA with Turkey's multiple range test. Here, compared to the PC group, final body weight (FBW), average daily gain (ADG), egg production (EP), egg weight (EW), average daily egg mass (EM), average daily feed intake (ADFI), and yield of abdominal fat (AFY) in the Met-group were lower, while EW and EM were higher in the Lys-group. The feed egg ratio (FER) was increased in the Met- and Lys-groups, and EW and AFY were decreased in the Ile-group compared to the controls. Meanwhile, ADG, EP, EM, and ADFI were lower in the Thr group than the PC group. The level of triglycerides (TGs) in the four groups was lower and the concentrations of uric acid (UA) in the Met-group were higher than those in the PC group. The shell color in the Thr group was lower than the PC group. Of note, amino acid deficiency altered the gut microbial structure (e.g., increasing the level of Parabacteroides and decreasing the abundance of Lactobacillus) in hens. The correlation analysis showed that amino acid deficiency-induced gut microbiota alteration is closely associated with the change in key parameters: FER, UA, AFY, EW, EM, TG, FBW, EP, and ADFI. Collectively, our results highlight the role of adequate amino acid ratio supplementation in the low-crude-protein diet structure for laying hens.

Influence of dietary Spirulina inclusion and lysozyme supplementation on the longissimus lumborum muscle proteome of newly weaned piglets

Arthrospira platensis (Spirulina) is a microalga with a high content of crude protein. It has a recalcitrant cell wall that limits the accessibility of the animal endogenous enzymes to its intracellular nutrients. Enzymatic supplementation aiming to degrade cell walls could benefit microalgae digestibility. The objective of this study was to evaluate the impact of dietary Spirulina and lysozyme supplementation over the muscle proteome of piglets during the post-weaning stage. Thirty piglets were randomly distributed among three diets: control (no microalga), SP (10% Spirulina) and SP + L (10% Spirulina +0.01% lysozyme). After 4 weeks, they were sacrificed and samples of the longissimus lumborum muscle were taken. The muscle proteome was analysed using a Tandem Mass Tag (TMT)-based quantitative approach. A total of 832 proteins were identified. Three comparisons were computed: SP vs Ctrl, SP + L vs Ctrl and SP + L vs SP. They had ten, four and twelve differentially abundant proteins. Glycogen metabolism and nutrient reserves utilization are increased in the SP piglets. Structural muscle protein synthesis increased, causing higher energy requirements in SP + L piglets. Our results demonstrate the usefulness of proteomics to disclose the effect of dietary microalgae, whilst unveiling putative mechanisms derived from lysozyme supplementation. Data available via ProteomeXchange with identifier PXD024083. SIGNIFICANCE: Spirulina, a microalga, is an alternative to conventional crops which could enhance the environmental sustainability of animal production. Due to its recalcitrant cell wall, its use requires additional measures to prevent anti-nutritional effects on the feeding of piglets in the post-weaning period, during which they endure post-weaning stress. One of such measures could be CAZyme supplementation to help degrade the cell wall during digestion. Muscle proteomics provides insightful data on the effect of dietary microalgae and enzyme activity on piglet metabolism.

The role of liver metabolism in compensatory-growth piglets induced by protein restriction and subsequent protein realimentation

The aim of this work was to study the role of hepatic metabolism of compensatory growth in piglets induced by protein restriction and subsequent protein realimentation. Thirty-six weaned piglets were randomly distributed in a control group and a treatment group. The control group piglets were fed with a normal protein level diet (18.83% CP) for the entire experimental period (day 1-28). The treatment group piglets were fed with a protein-restriction diet (13.05% CP) for day 1 to day 14, and the diet was restored to normal protein level diet for day 15 to day 28. RNA-seq is used to analyze samples of liver metabolism on day 14 and day 28, respectively. Hepatic RNA-sequencing analysis revealed that some KEGG signaling pathways involved in glycolipid metabolism (eg, "AMPK signaling pathway," "insulin signaling pathway," and "glycolysis or gluconeogenesis") were significantly enriched on day 14 and day 28. On day 14, protein restriction promoted hepatic lipogenesis by increasing the genes expression level of ACACA, FASN, GAPM, and SREBP1C, decreasing protein phosphorylation levels of AMPKɑ and ACC in AMPK signaling pathway. In contrast, on day 28, protein realimentation promoted hepatic gluconeogenesis by increasing the concentration of G6Pase and PEPCK, decreasing protein phosphorylation levels of IRS1, Akt, and FoXO1 in insulin signaling pathway. In addition, protein realimentation activated the GH-IGF1 axis between the liver and skeletal muscle. Overall, these findings revealed the importance of liver metabolism in achieving compensatory growth.

Effects of Dietary Histidine on Growth Performance, Serum Amino Acids, and Intestinal Morphology and Microbiota Communities in Low Protein Diet-Fed Piglets

Previous study showed that low protein diet-fed pigs are characterized by lower histidine concentration in the serum and muscle, suggesting that histidine may involve in protein-restricted response. Thus, the current study mainly investigated the effects of dietary histidine on growth performance, blood biochemical parameters and amino acids, intestinal morphology, and microbiota communities in low protein diet-challenged-piglets. The results showed that protein restriction inhibited growth performance, blood biochemical parameters and amino acids, and gut microbiota but had little effect on intestinal morphology. Dietary supplementation with histidine markedly enhanced serum histidine level and restored tryptophan concentration in low protein diet-fed piglets, while growth performance and intestinal morphology were not markedly altered in histidine-treated piglets. In addition, histidine exposure failed to affect bacterial diversity (observed species, Shannon, Simpson, Chao1, ACE, and phylogenetic diversity), but histidine-treated piglets exhibited higher abundances of Butyrivibrio and Bacteroides compared with the control and protein-restricted piglets. In conclusion, dietary histidine in low protein diet enhanced histidine concentration and affected gut microbiota (Butyrivibrio and Bacteroides) but failed to improve growth performance and intestinal morphology.

Branched-chain amino acids, especially of leucine and valine, mediate the protein restricted response in a piglet model

Branched-chain amino acids (BCAAs) are reduced in various protein restricted models, while the detailed role of BCAAs in protein restricted response is still obscure. Thus, the current study mainly investigated the amino acid metabolism in protein restricted piglets and the effects of BCAA balance in a low-protein diet on growth performance, amino acid metabolism, intestinal structure, and gut microbiota with focus on which BCAAs contributed to the protein restricted response. The results showed that protein restriction increased serum Ser, Thr, Ala, Lys, and Trp but reduced His, Cys, Val, and Ile levels. Intestinal amino acid transporters mainly mediated the mechanism of amino acid uptake. The BCAA balance refreshed the serum BCAA pool, which further improved growth performance in protein restricted piglets. Leu, Val, and Ile balances increased serum BCAA concentrations, respectively, and Leu and Val but not Ile enhanced the feed intake and weight gain in protein restricted piglets. In addition, protein restriction impaired the villus structure and increased the number of goblet cells in the ileum. Also, gut microbiota (Spirochaetales, Gammaproteobacteria, Lactobacillales at the order level) were altered in protein restricted pigs, while the BCAA balance markedly improved Gammaproteobacteria, Lactobacillales, and Aeromonadales proliferation, which might mediate growth promotion and amino acid metabolism. In conclusion, protein restriction markedly affected the host amino acid metabolism (i.e., Ser, Thr, Lys, His, BCAAs). The BCAA balance (especially for supplementation with Leu and Val) improved the amino acid metabolism, growth performance, and gut microbiota communities.

Impact of reduced dietary crude protein levels and phytase enzyme supplementation on growth response, slurry characteristics, and gas emissions of growing pigs

This experiment was carried out to evaluate the effect of reduced dietary crude protein (CP) levels supplemented with or without exogenous phytase on growing pigs. Six dietary treatments arranged in a 3 × 2 factorial arrangements of 3 CP levels (containing 14%, 16%, and 18% CP) supplemented each with or without 5,000 FTU/g phytase enzyme. Thirty growing pigs (average weight of 17.80 ± 0.10 kg) were allotted to the six dietary treatments in a complete randomized design. The final weight, daily weight gain, and feed conversion ratio (FCR) increased significantly with increasing CP levels. While, phytase supplementation improved (p = .044) FCR in pigs. Total solid and volatile solid content of the slurry were higher (p = .001) in pigs fed 14% and 16% CP diets supplemented with phytase when compared with other treatment groups. Concentration of methane gas emitted was lowest (p = .001) in the slurry of pigs fed 14% CP diet with or without phytase and those fed 16% CP diet with phytase supplementation. In conclusion, reduction in dietary CP levels resulted in reduced weight gain and poor FCR. While, reduced CP with phytase supplementation reduced concentration of methane gas emitted.

Integrated metabolomic and proteomics profiling reveals the promotion of Lactobacillus reuteri LR1 on amino acid metabolism in the gut–liver axis of weaned pigs

L. reuteri LR1 enhanced amino acid metabolism in the gut–liver axis of weaned pigs.