Immune system stimulation increases dietary threonine requirements for protein deposition in growing pigs

Dietary nutrition, intestinal microbiota dysbiosis and post-weaning diarrhea in piglets

Weaning is a critical transitional point in the life cycle of piglets. Early weaning can lead to post-weaning syndrome, destroy the intestinal barrier function and microbiota homeostasis, cause diarrhea and threaten the health of piglets. The nutritional components of milk and solid foods consumed by newborn animals can affect the diversity and structure of their intestinal microbiota, and regulate post-weaning diarrhea in piglets. Therefore, this paper reviews the effects and mechanisms of different nutrients, including protein, dietary fiber, dietary fatty acids and dietary electrolyte balance, on diarrhea and health of piglets by regulating intestinal function. Protein is an essential nutrient for the growth of piglets; however, excessive intake will cause many harmful effects, such as allergic reactions, intestinal barrier dysfunction and pathogenic growth, eventually aggravating piglet diarrhea. Dietary fiber is a nutrient that alleviates post-weaning diarrhea in piglets, which is related to its promotion of intestinal epithelial integrity, microbial homeostasis and the production of short-chain fatty acids. In addition, dietary fatty acids and dietary electrolyte balance can also facilitate the growth, function and health of piglets by regulating intestinal epithelial function, immune system and microbiota. Thus, a targeted control of dietary components to promote the establishment of a healthy bacterial community is a significant method for preventing nutritional diarrhea in weaned piglets.

Increased dietary Trp, Thr, and Met supplementation improves growth performance and protein deposition of salmonella-challenged growing pigs under poor housing conditions

Highly intensified rearing conditions and precarious sanitary management predispose pigs to immune system activation, altered amino acid (AA) metabolism, and decreased growth performance. Thus, the main objective of this study was to evaluate the effects of increased dietary tryptophan (Trp), threonine (Thr), and methionine + cysteine (Met + Cys) supplementation on performance, body composition, metabolism, and immune responses of group-housed growing pigs under challenging sanitary conditions. A hundred and twenty pigs (25.4 ± 3.7 kg) were randomly assigned to a 2 × 2 factorial arrangement, consisting of two sanitary conditions (SC, good [GOOD] or salmonella-challenge and poor housing condition [Salmonella Typhimurium (ST) + POOR]) and two diets, control (CN) or supplemented with AA (Trp, Thr, and Met + Cys:Lys ratios 20% higher than those of the CN diet [AA>+]). Pigs were followed during the growing phase (25-50 kg) and the trial lasted 28 d. The ST + POOR SC pigs were challenged with Salmonella Typhimurium and raised in a poor housing condition. The ST + POOR SC increased rectal temperature, fecal score, serum haptoglobin, and urea concentration (P < 0.05) and decreased serum albumin concentration (P < 0.05) compared with GOOD SC. Body weight, average daily feed intake, average daily gain (ADG), feed efficiency (G:F), and protein deposition (PD) were greater in GOOD SC than in ST + POOR SC (P < 0.01). However, pigs housed in ST + POOR SC fed with AA+ diet had lower body temperature (P < 0.05), increased ADG (P < 0.05) and nitrogen efficiency (P < 0.05), and a tendency for improved PD and G:F (P < 0.10) compared with CN diet fed pigs. Regardless of the SC, pigs fed AA+ diet had lower serum albumin (P < 0.05) and tended to decrease serum urea levels (P < 0.10) compared with CN diet. The results of this study suggest that the ratio of Trp, Thr, and Met + Cys to Lys for pigs are modified by sanitary conditions. Furthermore, supplementation of diets with a blend of Trp, Thr, and Met + Cys improves performance, especially under salmonella-challenge and poor housing conditions. Dietary tryptophan, threonine, and methionine supplementation can modulate immune status and influence resilience to sanitary challenges.

Review on Preventive Measures to Reduce Post-Weaning Diarrhoea in Piglets

In many countries, medical levels of zinc (typically as zinc oxide) are added to piglet diets in the first two weeks post-weaning to prevent the development of post-weaning diarrhoea (PWD). However, high levels of zinc constitute an environmental polluting agent, and may contribute to the development and/or maintenance of antimicrobial resistance (AMR) among bacteria. Consequently, the EU banned administering medical levels of zinc in pig diets as of June 2022. However, this may result in an increased use of antibiotic therapeutics to combat PWD and thereby an increased risk of further AMR development. The search for alternative measures against PWD with a minimum use of antibiotics and in the absence of medical levels of zinc has therefore been intensified over recent years, and feed-related measures, including feed ingredients, feed additives, and feeding strategies, are being intensively investigated. Furthermore, management strategies have been developed and are undoubtedly relevant; however, these will not be addressed in this review. Here, feed measures (and vaccines) are addressed, these being probiotics, prebiotics, synbiotics, postbiotics, proteobiotics, plants and plant extracts (in particular essential oils and tannins), macroalgae (particularly macroalgae-derived polysaccharides), dietary fibre, antimicrobial peptides, specific amino acids, dietary fatty acids, milk replacers, milk components, creep feed, vaccines, bacteriophages, and single-domain antibodies (nanobodies). The list covers measures with a rather long history and others that require significant development before their eventual use can be extended. To assess the potential of feed-related measures in combating PWD, the literature reviewed here has focused on studies reporting parameters of PWD (i.e., faeces score and/or faeces dry matter content during the first two weeks post-weaning). Although the impact on PWD (or related parameters) of the investigated measures may often be inconsistent, many studies do report positive effects. However, several studies have shown that control pigs do not suffer from diarrhoea, making it difficult to evaluate the biological and practical relevance of these improvements. From the reviewed literature, it is not possible to rank the efficacy of the various measures, and the efficacy most probably depends on a range of factors related to animal genetics and health status, additive doses used, composition of the feed, etc. We conclude that a combination of various measures is probably most recommendable in most situations. However, in this respect, it should be considered that combining strategies may lead to additive (e.g., synbiotics), synergistic (e.g., plant materials), or antagonistic (e.g., algae compounds) effects, requiring detailed knowledge on the modes of action in order to design effective strategies.

The Amino Acids Sensing and Utilization in Response to Dietary Aromatic Amino Acid Supplementation in LPS-Induced Inflammation Piglet Model

Dietary supplementation with aromatic amino acids (AAAs) has been demonstrated to alleviate intestinal inflammation induced by lipopolysaccharide (LPS) in the piglets. But the mechanism of AAA sensing and utilization under inflammatory conditions is not well-understood. The study was conducted with 32 weanling piglets using a 2 × 2 factorial arrangement (diet and LPS challenge) in a randomized complete block design. Piglets were fed as basal diet or the basal diet supplemented with 0.16% tryptophan (Trp), 0.41% phenylalanine (Phe), and 0.22% tyrosine (Tyr) for 21 days. The results showed that LPS treatment significantly reduced the concentrations of cholecystokinin (CCK) and total protein but increased leptin concentration, the activities of alanine transaminase, and aspartate aminotransferase in serum. Dietary supplementation with AAAs significantly increased the serum concentrations of CCK, peptide YY (PYY), and total protein but decreased the blood urea nitrogen. LPS challenge reduced the ileal threonine (Thr) digestibility, as well as serum isoleucine (Ile) and Trp concentrations, but increased the serum concentrations of Phe, Thr, histidine (His), alanine (Ala), cysteine (Cys), and serine (Ser) (P < 0.05). The serum-free amino acid concentrations of His, lysine (Lys), arginine (Arg), Trp, Tyr, Cys, and the digestibilities of His, Lys, Arg, and Cys were significantly increased by feeding AAA diets (P < 0.05). Dietary AAA supplementation significantly increased the serum concentrations of Trp in LPS-challenged piglets (P < 0.05). In the jejunal mucosa, LPS increased the contents of Ala and Cys, and the mRNA expressions of solute carrier (SLC) transporters (i.e., SLC7A11, SLC16A10, SLC38A2, and SLC3A2), but decreased Lys and glutamine (Gln) contents, and SLC1A1 mRNA expression (P < 0.05). In the ileal mucosa, LPS challenge induced increasing in SLC7A11 and SLC38A2 and decreasing in SLC38A9 and SLC36A1 mRNA expressions, AAAs supplementation significantly decreased mucosal amino acid (AA) concentrations of methionine (Met), Arg, Ala, and Tyr, etc. (P < 0.05). And the interaction between AAAs supplementation and LPS challenge significantly altered the expressions of SLC36A1 and SLC38A9 mRNA (P < 0.05). Together, these findings indicated that AAAs supplementation promoted the AAs absorption and utilization in the small intestine of piglets and increased the mRNA expressions of SLC transports to meet the high demands for specific AAs in response to inflammation and immune response.

Evaluation of a novel threonine source for nursery pig diets

Four hundred and eighty (PIC 337 X 1050, PIC Genus, Hendersonville, TN) pigs were used to evaluate a novel threonine source (ThrPro, CJ America Bio, Fort Dodge, IA) for nursery pigs from approximately 7 to 20 kg body weight (BW). After weaning, pigs were sorted by sex and fed a common diet for 1 wk. Upon completion of the first week, pigs were sorted into randomized complete blocks, equalized by weight, within 16 replications. Pigs were allocated to one of three dietary treatments: positive control (POS)—standard ileal digestible threonine-to-lysine ratio (SID; Thr:Lys) 0.60, negative control (NEG)—SID Thr:Lys ≤0.46, and alternative Thr source (TEST)—SID Thr:Lys 0.60. The alternative Thr source included fermentative biomass and was assumed to contain 75% Thr and a digestibility coefficient of 100% based on the manufacturer’s specifications. All other nutrients met or exceeded the NRC recommendations. Growth and intake data were analyzed as repeated measures with a compound symmetry covariance structure using the MIXED procedure in SAS 9.4 (SAS Institute Inc., Cary, NC) with pen as the experimental unit. Treatment, phase, the interaction between treatment and phase, and block were included as fixed effects in the model. Differences in total removals were tested using Fisher’s Exact Test of PROC FREQ. Results were considered significant at P ≤ 0.05 and considered a trend at P > 0.05 and P ≤ 0.10. During the first 14 d, pigs fed TEST had decreased gain-to-feed ratio (G:F; 0.77 vs. 0.80, P = 0.022) compared to POS and increased G:F (0.77 vs. 0.73, P < 0.001) compared to NEG. Over days 14–28, pigs fed TEST had similar G:F (0.71 vs. 0.70, P = 0.112) compared to POS and increased G:F (0.71 vs. 0.63, P < 0.001) compared to NEG. Overall (days 0–28), pigs fed TEST had similar average daily gain (ADG; 0.47 vs. 0.47 kg/d, P = 0.982) and G:F (0.76 vs. 0.74, P = 0.395) compared to POS and increased ADG (0.47 vs. 0.43 kg/d, P < 0.001) and G:F (0.76 vs. 0.67, P < 0.001) compared to NEG. The average daily feed intake was not significantly different across treatments for the entirety of the study. In conclusion, the replacement of crystalline L-Thr with a novel Thr source resulted in similar growth performance in nursery pigs from approximately 7 to 20 kg.

Effects of divergent selection for residual feed intake on nitrogen metabolism and lysine utilization in growing pigs

A study was conducted to evaluate the effects of divergent genetic selection for residual feed intake (RFI) on nitrogen (N) metabolism and lysine utilization in growing pigs. Twenty-four gilts (body weight [BW] 66 ± 5 kg) were selected from generation nine of the low RFI (LRFI; n = 12) and high RFI (HRFI; n = 12) Iowa State University Yorkshire RFI selection lines. Six pigs from each genetic line were assigned to each of two levels of lysine intake: 70% and 100% of estimated requirements based on the potential of each genetic line for protein deposition (PD) and feed intake. For all diets, lysine was first limiting among amino acids. Using isotope tracer, N-balance, and nutrient digestibility evaluation approaches, whole-body N metabolism and the efficiency of lysine utilization were determined for each treatment group. No significant interaction effects of line and diet on dietary N or gross energy digestibility, PD, and the efficiency of lysine utilization for PD were observed. The line did not have a significant effect on PD and digestibility of dietary N and GE. An increase in lysine intake improved N retention in both lines (from 15.0 to 19.6 g/d, SE 1.44, in LRFI pigs; and from 16.9 to 19.8 g/d, SE 1.67, in HRFI pigs; P < 0.01). At the low lysine intakes and when lysine clearly limited PD, the efficiency of using available lysine intake (above maintenance requirements) for PD was 80% and 91% (SE 4.6) for the LRFI and HRFI pigs, respectively (P = 0.006). There were no significant effects of line or of the line by diet interaction on N flux, protein synthesis, and protein degradation. Lysine intake significantly increased (P < 0.05) N flux (from 119 to 150, SE 8.7 g/d), protein synthesis (from 99 to 117, SE 10.6 g of N/d), and protein degradation (from 85 to 100, SE 6.6 g of N/d). The protein synthesis-to-retention ratio tended to be higher in the LRFI line compared with the HRFI line (6.5 vs. 5.8 SE 0.62; P = 0.06), indicating a tendency for the lower efficiency of PD in this group. Collectively, these results indicate that genetic selection for low RFI is not associated with improvements in lysine utilization efficiency, protein turnover, and nutrient digestibility.

Effect of supplemental threonine above requirement on growth performance of Salmonella typhimurium challenged pigs fed high-fiber diets1

It was shown previously that high dietary fiber (DF) and immune system stimulation (ISS) with systemic Escherichia coli lipopolysaccharide independently increased the threonine (Thr) requirement to maximize growth performance and protein deposition (PD). However, no additive effects on the Thr requirement were observed when both DF and ISS were present. The objective of the present study was to investigate whether supplementing Thr to meet previously estimated requirements for high DF and systemic immune challenge would maintain performance of pigs exposed to an enteric immune challenge when fed high DF. A total of 128 pigs (22.6 ± SD = 1.6 kg initial BW) were assigned to 1 of 4 dietary treatments in a 2 × 2 factorial arrangement in a randomized complete block design (n = 8 pens/treatment and 4 pigs/pen) for 28 d. Treatments were a low-fiber (LF; 13% total DF) or high-fiber (HF; 20% total DF) diet with either a standard (STD; 0.65% SID) or supplemental (SUP; 0.78% SID) Thr level. After a 7-d adaptation, pigs were orally inoculated with 2 mL (2.3 × 109 CFU/mL) of Salmonella typhimurium (ST). Blood samples and rectal swabs were obtained and rectal temperature recorded to determine clinical responses and ST shedding. On day 7 postinoculation, 1 pig/pen was euthanized and mesenteric lymph nodes, spleen, and digesta (ileum, cecum, and colon) were sampled to assess ST colonization and translocation. Body weight and feed intake were recorded on day 0, 7, and 21 postinoculation to calculate ADG, ADFI, and G:F. Rectal temperature increased (P < 0.05) 24 h postinoculation and remained elevated at day 6. Serum albumin concentration decreased (P < 0.05), whereas haptoglobin concentration increased (P < 0.05) postinoculation. There was no fiber or Thr effect (P > 0.05) on ST counts in the ileum and cecum, but a fiber × Thr interaction (P < 0.05) was observed in the colon. Supplemental Thr improved (P < 0.05) growth performance in LF- and HF-fed challenged pigs. However, performance of supplemented HF challenged pigs was less than (P < 0.05) supplemented LF challenged pigs. These results suggest that Thr supplemented to meet requirements for high DF and systemic immune challenge was not sufficient to maintain growth performance of pigs fed HF diets and challenged with an enteric pathogen.

Immune System Stimulation Reduces the Efficiency of Whole-Body Protein Deposition and Alters Muscle Fiber Characteristics in Growing Pigs

Simple Summary

Disease reduces growth and protein retention in pigs. Protein retention is the balance between two energy-consuming processes in the body of pigs: protein synthesis and breakdown. Previous reports on the effects of disease on these components of protein metabolism and their consecutive effects on protein retention are inconsistent. In addition, limited information is available about the effects of disease on the composition of muscle fibers in pigs. Thus, we evaluated these parameters, since they help us to understand protein metabolism during disease in pigs. We used twelve gilts; five were used as a control and seven were made ill. Experimental diets were designed to supply nutrients that closely met the daily requirements of each group. Protein synthesis, protein breakdown, and protein retention were measured over 72 h. Pigs were then euthanized and various muscles were sampled. Our findings suggested that disease not only reduces protein retention by decreasing protein synthesis and protein breakdown, but also by reducing the efficiency of protein deposition. In other words, ill pigs synthesize more protein per unit of protein retention, compared to healthy pigs. In addition, disease reduces muscle mass and changes the composition of the muscle fibers. The latter might negatively affect pork quality.

Abstract

The effects of immune system stimulation (ISS), induced by repeated injection of Escherichia coli lipopolysaccharide, on the whole-body protein synthesis versus degradation rates, the efficiency of protein deposition (PD), and muscle fiber characteristics in pigs were evaluated. Twelve growing gilts were assigned to two levels of amino acid intake that was predicted based on the potential of each group’s health status for PD and feed intake. Isotope tracer, nitrogen balance, and immunohistochemical staining techniques were used to determine protein turnover, PD, and muscle fiber characteristics, respectively. Protein synthesis, degradation, and PD were lower in immune-challenged pigs than in control pigs (p < 0.05). Strong tendencies for a higher protein synthesis-to-PD ratio (p = 0.055) and a lower protein synthesis-to-degradation ratio (p = 0.065) were observed in immune-challenged pigs. A decrease in muscle cross-sectional area of fibers and a shift from myosin heavy chain (MHC)-II towards MHC-I fibers (p < 0.05) were observed in immune-challenged pigs. These results indicated that ISS reduces PD not only by suppressing the whole-body protein synthesis and degradation rates, but also by decreasing the efficiency of PD in growing pigs. In addition, ISS induces atrophy in skeletal muscles and favors a slow-twitch oxidative fiber type composition.

Amino Acids Influencing Intestinal Development and Health of the Piglets

Simple Summary

The health of piglets is an important issue in pig production. Nutritional support for intestinal development is a significant component of piglet care, and amino acids are essential for intestinal growth and development. For suckling piglets, the sows’ milk and the maternal environment shape the structure and support the function of the intestinal tract. The composition of milk affects intestinal morphology and the digestive, absorption and barrier function. After weaning, the optimal nutritional strategies of their diet are necessary to guarantee the piglets’ intestinal development and growth performance. Amino acids are the most important ingredient in piglet diets. The aim of this review is to collect and analyze the relationship between amino acid nutrition and intestinal development of piglets, and elucidate the impacts on piglet health.

Abstract

The amino acids and other components of diet provide nourishment for piglet intestinal development and maturation. However, early-weaned piglets struggle with tremendous stress, impairing normal intestinal health and leading to intestinal dysfunction and even death. The high prevalence worldwide of post-weaning diarrhoea syndrome (PWDS) in piglets has led to much interest in understanding the important role of nutrients in the establishment and maintenance of a functional intestinal tract. In particular, the impacts of amino acids on these functions must be considered. Amino acid levels greatly influence intestinal development in weaning piglets. The lack of amino acids can cause marked structural and functional changes in the intestine. Therefore, a comprehensive understanding of the functions of amino acids is necessary to optimize amino acid requirements of the developing intestinal tract to maximize piglet health and growth performance. This review summarizes the role of specific amino acids (arginine, glutamate, threonine, sulphur-containing amino acids (SCAAs), and branched-chain amino acids (BCAAs)) that have been proven to be beneficial for the intestinal health of weaned piglets.