Metabolomic profiling in umbilical venous plasma reveals effects of dietary rumen-protected arginine or N-carbamylglutamate supplementation in nutrient-restricted Hu sheep during pregnancy

L-Arginine supplementation in pregnancy: a systematic review of maternal and fetal outcomes

BACKGROUND/AIM OF THE STUDY

L-Arginine (L-Arg)/Nitric Oxide (NO) system is involved in the pathophysiology of relevant Obstetric conditions. This review aims at summarizing the effects of L-Arg supplementation in pregnancy looking at safety and efficacy.

METHODS

We conducted a systematic review of the literature utilizing PubMed for studies published from inception to September 2022. The search included human and animal studies where L-Arg was supplemented pre-conceptionally or during pregnancy, by either oral or intravenous route. The main perinatal outcomes were focused.

RESULTS

Among 1028 publications, 51 studies were eligible for inclusion, 25 were performed in women, and the remnant in animals. Compared to controls/placebo, the supplementation with L-Arg reduced the development of pre-eclampsia (four studies), decreased blood pressure, and reduced the need for antihypertensive drugs in women with Hypertensive Disorders of Pregnancy (HDP, eight studies). In women carrying growth retarded fetuses, L-Arg improved fetoplacental circulation, birth weight and neonatal outcomes (five studies), while in the case of threatened preterm birth, L-Arg reduced uterine contractions (two studies). In several animal species, L-Arg supplementation in pregnancy improved reproductive performance by increasing the litter number and size. Moreover, in pre-eclamptic and metabolic syndrome experimental models, maternal hypertension and fetal growth were improved.

CONCLUSION

L-Arg displays biological activities in pregnancies complicated by HDP and growth restriction, both in women and animal models. L-Arg administration is safe and could be a candidate as an intervention beneficial to maternal and fetal outcomes, at least in moderate clinical disorders.

Effects of dietary N-carbamylglutamate on rumen fermentation parameters, and bacterial community diversity of Holstein dairy cows in Tibet

Introduction

The Tibetan Plateau is characterized by low temperature and hypoxia. N-carbamylglutamic acid (NCG) can increase blood oxygen saturation, and have the potential to be used to prevent the high-altitude hypoxia stress state of cows. However, its beneficial effect on the rumen microbiota of Holstein dairy cows remains unclear.

Methods

Hence, the experiments 12 multiparous (parity ranged from 2 to 7) Holstein dairy cows (413.0 ± 42 kg) were randomly assigned to 2 treatments with 6 replicates in each treatment: basal diet (CON, control group) and basal diet plus 20 g/d/cow of NCG (NCG, experiment group), respectively. To study the effects of dietary NCG supplementation on rumen microbiota of Holstein dairy cows in Tibet. The experiment lasted for 45 days, with 15 days of pre-feeding and 30 days of formal trail period.

Results

The results showed that ruminal NH₃-N concentration in NCG group was lower (p < 0.05) than that in the CON group, while molar proportion of acetic acid and total volatile fatty acid (VFA) concentration were increased (p < 0.05) with the addition of NCG. Microbial diversity increased (p < 0.05) in NCG group, with Bacteroidetes, Firmicutes, and Patescibacteria as the most abundant phyla. The KEGG pathway analysis showed that the potential function of ruminal bacteria was mainly enriched in metabolism (carbohydrates, amino acids, lipids, energy, and nucleotides) and genetic information processing (replication, repair, and translation).

Conclusion

In conclusion, NCG can improve rumen nitrogen utilization, total VFA and acetic acid production, and increase rumen microbial diversity, all of which could make the introduced Holstein dairy cows to better adapt to the harsh environment in Tibet and improve their production performance.

The significance of N-carbamoylglutamate in ruminant production

Improving the efficiency and production of grazing ruminants to support food and fiber production, while reducing the environmental footprint and meeting the welfare needs of the animals, is important for sustainable livestock production systems. Development of new technologies that can improve the efficiency of nitrogen (N) utilization in ruminants, and that are effective and safe, has important implications for ruminant livestock production. N-carbomoylglutamate (NCG) is a functional micronutrient that stimulates endogenous synthesis of arginine, which can improve survival, growth, lactation, reproductive performance, and feed efficiency in mammals. There is a growing body of evidence to support the potential of dietary NCG supplementation to improve the productive capacity and N utilization efficiency of ruminants. This review summarizes the current literature on the effects of dietary supplementation with NCG in ruminants and impacts on production and potential to reduce the environmental footprint of farmed ruminant livestock. The current literature highlights the potential for commercial application in ruminant livestock to improve productivity and N utilization efficiency.

Microbiome-Metabolome Responses in Ruminal Content and Feces of Lactating Dairy Cows With N-Carbamylglutamate Supplementation Under Heat Stress

The objective of the present study was to investigate the effects of N-carbamylglutamate (NCG) supplementation on metabolic profile and microbiota in ruminal content and feces of lactating dairy cows under heat stress (HS). Forty-eight lactating Holstein cows (154 ± 13.6 days in milk) were assigned randomly to four treatments (n = 12), to receive 0, 15, 20, or 25 g/day of commercial NCG (proportion: 97.7%) for the period of 60 days. The recorded ambient temperature–humidity index (THI) suggested that the cows were exposed to HS for almost the entire experimental period (average THI: 80.6). Samples of ruminal content and feces were collected at the end of the trial (day 60) to determine the biological effects of NCG supplementation on metabolome and microbiota using mass spectrometry-based metabolomics and 16S rRNA gene sequencing techniques, respectively. Results showed that NCG supplementation enhanced the levels of ruminal microbial protein, total volatile fatty acids (VFAs), and the molar proportion of propionate in the rumen, but lowered the ruminal pH, ammonia nitrogen (NH3-N), and the ratio of acetate to propionate. NCG at doses of 20 and 25 g/day reduced the community richness and diversity of ruminal microbiota with the decrease of Shannon and Simpson diversity. Compositions of ruminal and fecal microbiotas were altered by NCG, and the PICRUSt results revealed that metabolic pathways of the bacteria, such as amino acid metabolism, energy metabolism, and pyruvate metabolism, were enriched in NCG groups. Distinct changes in the metabolomic profile of ruminal fluid were observed between the control and NCG groups. Changes of 26 metabolites mainly involved in arginine metabolism, glutamate metabolism, and nitrogen metabolism were observed associated with NCG supplementation. These results provided new insights into the effects of NCG on metabolomic profile and microbiota in ruminal content and feces, and the optimal dose of NCG supplemented to dairy cows was 20 g/hd/day, which contributed to understanding the effects of NCG on HS in lactating dairy cows.

Effects of dietary supplementation with N-carbamylglutamate on maternal endometrium and fetal development during early pregnancy in Inner Mongolia white cashmere goats

This study investigated the effects of dietary supplementation with N-carbamylglutamate (NCG) on maternal endometrium and fetal development during early pregnancy of Inner Mongolia white cashmere goats. Forty-eight pregnant Inner Mongolia white cashmere goats (average age 3 years old, average lactation parity 2, and average body weight 43.81 ± 2.66 kg) were randomly allocated to three groups: a basal diet (control group, n = 16), a basal diet plus 0.30-g NCG/d (NCG1 group, n = 16), and a basal diet plus 0.40-g NCG/d (NCG2 group, n = 16). All of the does were housed in individual pens and the NCG treatment was conducted from Days 0 to 90 of pregnancy. At Days 17 and 90 of pregnancy, six representative pregnant does in each group were slaughtered. The current study results demonstrated that maternal NCG administration during early pregnancy effectively increased the arginine family of amino acids and the glucogenic amino acids concentrations and promoted the mRNA expression of osteopontin (OPN), αv and β3 integrins, and endometrial development of Inner Mongolia white cashmere goats. The supplementation improved the fetal brown adipose tissue (BAT) stores and the mRNA expression of UCP-1 and BMP7, thereby helping to the fetal early development.

Integration of Multiplied Omics, a Step Forward in Systematic Dairy Research

Due to their unique multi-gastric digestion system highly adapted for rumination, dairy livestock has complicated physiology different from monogastric animals. However, the microbiome-based mechanism of the digestion system is congenial for biology approaches. Different omics and their integration have been widely applied in the dairy sciences since the previous decade for investigating their physiology, pathology, and the development of feed and management protocols. The rumen microbiome can digest dietary components into utilizable sugars, proteins, and volatile fatty acids, contributing to the energy intake and feed efficiency of dairy animals, which has become one target of the basis for omics applications in dairy science. Rumen, liver, and mammary gland are also frequently targeted in omics because of their crucial impact on dairy animals’ energy metabolism, production performance, and health status. The application of omics has made outstanding contributions to a more profound understanding of the physiology, etiology, and optimizing the management strategy of dairy animals, while the multi-omics method could draw information of different levels and organs together, providing an unprecedented broad scope on traits of dairy animals. This article reviewed recent omics and multi-omics researches on physiology, feeding, and pathology on dairy animals and also performed the potential of multi-omics on systematic dairy research.

Application of Metabolomics in Diagnosis of Cow Mastitis: A Review

Cow mastitis, with high incidence rate and complex cause of disease, is one of the main diseases that affect the development of dairy industry in the world. Clinical mastitis and subclinical mastitis caused by Staphylococcus aureus, Escherichia coli, Streptococcus, and other pathogens have a huge potential safety hazard to food safety and the rapid development of animal husbandry. The economic loss caused by cow mastitis is billions of dollars every year in the world. In recent years, the omics technology has been widely used in animal husbandry with the continuous breakthrough of sequencing technology and the continuous reduction of sequencing cost. For dairy cow mastitis, the traditional diagnostic technique, such as histopathological screening, somatic cell count, milk pH test, milk conductivity test, enzyme activity test, and infrared thermography, are difficult to fully and comprehensively clarify its pathogenesis due to their own limitations. Metabolomics technology is an important part of system biology, which can simultaneously analyze all low molecular weight metabolites such as amino acids, lipids, carbohydrates under the action of complex factors including internal and external environment and in a specific physiological period accurately and efficiently, and then clarify the related metabolic pathways. Metabolomics, as the most downstream of gene expression, can amplify the small changes of gene and protein expression at the level of metabolites, which can more fully reflect the cell function. The application of metabolomics technology in cow mastitis can analyze the hetero metabolites, identify the related biomarkers, and reveal the physiological and pathological changes of cow mammary gland, so as to provide valuable reference for the prediction, diagnosis, and treatment of mastitis. The research progress of metabolomics technology in cow mastitis in recent years was reviewed, in order to provide guidance for the development of cow health and dairy industry safety in this manuscript.

Effects of mid-gestational l-citrulline supplementation to twin-bearing ewes on umbilical blood flow, placental development, and lamb production traits

The objective of the study was to examine how l-citrulline supplementation to ewes during mid-gestation influences placental activity, placental blood flow, lamb body weight, and carcass characteristics. Two studies were completed. A pharmacokinetic study to compare circulating plasma amino acid concentrations after a single intravenous injection of 155 µmol/kg BW l-citrulline or after an isonitrogenous amount of l-alanine (control; 465 µmol/kg BW). Increases (P < 0.05) in circulating citrulline concentrations were detected for 8 h after l-citrulline injection versus the control. Similarly, increases (P < 0.05) in circulating arginine concentrations were detected for 24 h after l-citrulline treatment. The second study used 12 ewes with twin pregnancies. Daily intravenous injections of either l-citrulline or l-alanine were administered for 39 d from d 42–45 to 81–84 of gestation. Ewes were limit-fed at 85% daily energy requirements during the injection period. A decrease (P < 0.0001) in body weight was observed in both treatment groups during this period. No treatment differences were observed in circulating pregnancy-specific protein B concentrations or placental blood flow during the treatment and post-treatment gestational period. No treatment differences were observed in lamb survival nor in lamb birth, weaning and slaughter weights. Treatment did not influence lamb carcass composition or organ weights. However, there was a tendency (P = 0.10) for an increase in antral follicle numbers in ovaries from ewe lambs derived from ewes treated with l-citrulline. In summary, a daily l-citrulline injection increased both circulating citrulline and arginine concentrations in ewes, but daily l-citrulline injections during mid-gestation did not produce any detectable changes in placental activity and blood flow, neonatal and postnatal lamb development, and lamb carcass composition at slaughter. In conclusion, no benefits in placental function and lamb development were observed after providing l-citrulline during mid-gestation in ewes exposed to a mild energy restriction, but there was an indication that follicle numbers in ewe lambs were positively influenced by l-citrulline treatment during fetal development.

Effects of Dietary N-carbamylglutamate on Growth Performance, Apparent Digestibility, Nitrogen Metabolism and Plasma Metabolites of Fattening Holstein Bulls

N-carbamylglutamate (NCG), a structural analog of N-acetylglutamate, improves nitrogen utilization in dairy cows. However, the effects of NCG on bulls are unknown. The purpose of the current research was to investigate the effects of adding different amounts of NCG on growth performance, nutrient digestibility, nitrogen metabolism and plasma metabolites of fattening Holstein bulls. Twenty-four Holstein bulls with similar body weights (BW, 408 ± 21.9 kg) and ages (450 ± 6.1 d; all mean ± SD) were selected for the feeding trial. After 2 weeks of adaptation, bulls were blocked by BW and age and subsequently randomly assigned to 1 of 4 groups: (1) CON group (control diet), (2) L group (supplementation with 20 mg/kg BW NCG), (3) M group (supplementation with 40 mg/kg BW NCG), or (4) H group (supplementation with 80 mg/kg BW NCG). The addition of NCG linearly and quadratically increased the average daily gain (CON vs. L vs. M vs. H = 1.03 vs. 1.19 vs. 1.40 vs. 1.26 kg/d) (p < 0.05), feed conversion ratio (CON vs. L vs. M vs. H = 11.92 vs. 9.22 vs. 7.76 vs. 8.62) (p < 0.05), crude protein digestibility (CON vs. L vs. M vs. H = 64.3 vs. 63.8 vs. 67.7 vs. 65.8%) (0.05 < p < 0.10), N retention (p < 0.05) and N utilization (p < 0.05) of bulls, whereas the contents of fecal N (0.05 < p < 0.10) and urinary N (0.05 < p < 0.10) in NCG-fed bulls linearly decreased compared with those in CON bulls. Bulls fed NCG showed a quadratic increased plasma nitric oxide (p < 0.05) concentration. Furthermore, Arg (p < 0.05), Ile (p < 0.05), Val (p < 0.05), Ala (p < 0.05), Glu (p < 0.05), Ser (p < 0.05), total essential amino acid (p < 0.05) and total nonessential amino acid (p < 0.05) concentrations linearly and quadratically increased with increasing doses of NCG. In contrast, plasma urea (p < 0.05) and ammonia (p < 0.05) concentration linearly and quadratically decreased with increasing doses of NCG. Overall, the addition of NCG increased plasma Arg, Ile, Val, TEAA and TNEAA concentration, which in turn resulted in a higher N utilization and, therefore, higher average daily gain in NCG-fed bulls, providing baseline data for the widespread application of NCG in beef cattle production.

Prenatal Amino Acid Supplementation to Improve Fetal Growth: A Systematic Review and Meta-Analysis

Aberrant fetal growth remains a leading cause of perinatal morbidity and mortality and is associated with a risk of developing non-communicable diseases later in life. We performed a systematic review and meta-analysis combining human and animal studies to assess whether prenatal amino acid (AA) supplementation could be a promising approach to promote healthy fetal growth. PubMed, Embase, and Cochrane libraries were searched to identify studies orally supplementing the following AA groups during gestation: (1) arginine family, (2) branched chain (BCAA), and (3) methyl donors. The primary outcome was fetal/birth weight. Twenty-two human and 89 animal studies were included in the systematic review. The arginine family and, especially, arginine itself were studied the most. Our meta-analysis showed beneficial effects of arginine and (N-Carbamyl) glutamate (NCG) but not aspartic acid and citrulline on fetal/birth weight. However, no effects were reported when an isonitrogenous control diet was included. BCAA and methyl donor supplementation did not affect fetal/birth weight. Arginine family supplementation, in particular arginine and NCG, improves fetal growth in complicated pregnancies. BCAA and methyl donor supplementation do not seem to be as promising in targeting fetal growth. Well-controlled research in complicated pregnancies is needed before ruling out AA supplements or preferring arginine above other AAs.

Dietary Supplementation of L-Arginine and N-Carbamylglutamate Attenuated the Hepatic Inflammatory Response and Apoptosis in Suckling Lambs with Intrauterine Growth Retardation

L-arginine (Arg) is a semiessential amino acid with several physiological functions. N-Carbamylglutamate (NCG) can promote the synthesis of endogenous Arg in mammals. However, the roles of Arg or NCG on hepatic inflammation and apoptosis in suckling lambs suffering from intrauterine growth restriction (IUGR) are still unclear. The current work is aimed at examining the effects of dietary Arg and NCG on inflammatory and hepatocyte apoptosis in IUGR suckling lambs. On day 7 after birth, 48 newborn Hu lambs were selected from a cohort of 432 twin lambs. Normal-birthweight and IUGR Hu lambs were allocated randomly (n = 12/group) to control (CON), IUGR, IUGR+1% Arg, or IUGR+0.1% NCG groups. Lambs were fed for 21 days from 7 to 28 days old. Compared with CON lambs, relative protein 53 (P53), apoptosis antigen 1 (Fas), Bcl-2-associated X protein (Bax), caspase-3, cytochrome C, tumor necrosis factor alpha (TNF-α), nuclear factor kappa-B (NF-κB) p65, and NF-κB pp65 protein levels were higher (P < 0.05) in liver from IUGR lambs, whereas those in liver from IUGR lambs under Arg or NCG treatment were lower than those in IUGR lambs. These findings indicated that supplementing Arg or NCG reduced the contents of proinflammatory cytokines at the same time when the apoptosis-related pathway was being suppressed, thus suppressing the IUGR-induced apoptosis of hepatic cells.

Application of N-carbamylglutamate in Rex rabbits to reduce body fat deposition and its possible mechanism

N-Carbamylglutamate (NCG) has been shown to enhance arginine synthesis and improve growth performance in animals. However, the effect of NCG on body fat deposition remains unknown. This study examined the effects of NCG on body fat deposition and evaluated the potential mechanisms involved. Rex rabbits (3 months old) were assigned to one of four dietary groups and supplemented with NCG at the following different concentrations in a feeding trial that lasted 67 d: 0 (control), 0·04, 0·08, and 0·12 %. NCG supplementation increased serum concentrations of arginine and proline by activating intestinal carbamoylphosphate synthase-І at the posttranscriptional level. Final body weights and growth performance were not affected by dietary NCG levels. However, NCG-treated rabbits had lower perirenal and subcutaneous fat percentages, serum TAG content, and hepatic fatty acid synthase (FAS) activity and increased NO synthase activity and serum levels of NO, growth hormone (GH), and insulin-like growth factor 1 (IGF-1). There were significant positive correlations between TAG content and perirenal fat percentage, as well as FAS activity and perirenal fat percentage, but significant negative correlations between TAG and NO levels, and FAS activity and IGF-1 level in rabbits after NCG treatment. NCG supplementation did not affect hepatic health indicators, except for serum ammonia concentrations, which were decreased in NCG-treated rabbits. Our results suggest that NCG can serve as a dietary supplement to reduce unfavourable fat deposition through inhibiting hepatic lipogenesis in animals since it appears to have no negative effects on growth performance or hepatic health.

The suppressed autophagy induced by carbon disulfide could be rescued by N-carbamoyl glutamate during the window of embryo implantation in mice

OBJECTIVES

To explore the effects of carbon disulfide (CS₂) and N-carbamoyl glutamate (NCG) on autophagy during the window of embryo implantation in mice and whether dietary NCG supplementation can promote embryo implantation in case of CS₂ exposure.

METHODS

Pregnant mice that received single intraperitoneal injection of CS₂ on Gestational day (GD)4 were fed basal diet with or without NCG supplementation from GD1 to endpoints. The control mice were injected solvents. There were four endpoints (GD5, GD6, GD7 and GD9 endpoints) in each group. The uterus was collected on endpoints to detect autophagy-related markers by using the methods of transmission electron microscopy (TEM), immunohistochemistry (IHC), quantitative real-time polymerase chain reaction (qRT-PCR) and ELISA.

RESULTS

The P62 brown punctate staining increased in CS₂ exposure group and reduced after dietary NCG supplementation, which was opposite with LC3B, Beclin1 and ATG5 on GD5 endpoint. Simultaneously, P62 protein expression raised 43.33% on GD5 endpoint (p < 0.01) when exposed to CS₂ and descended to the control level after NCG supplementation. The rate of decline of LC3B and Beclin1 proteins were 27.04% (p < 0.01) and 23.27% (p < 0.05) on GD5 endpoint, 20.20% (p < 0.05) and 11.30% on GD7 endpoint in CS₂ exposure group, respectively, then NCG supplementation caused the LC3B and Beclin1 protein expression to rise in different degrees. Comparatively, the mRNA expression of all autophagy-related gene changed more apparently on three endpoints than the protein expression. The images of TEM showed that nearly no autophagosome could be seen in CS₂ exposure group, while dietary NCG supplementation increased the number of autophagosome obviously on GD5 endpoint. The number of implanted embryos which declined due to CS₂ exposure returned to normal in NCG supplementation group.

CONCLUSIONS

Dietary NCG supplementation could rescue the suppressed autophagy induced by CS₂ in the window of implantation and increase the number of implanted embryos.

Dietary rumen-protected arginine and N-carbamylglutamate supplementation enhances fetal growth in underfed ewes

The present study was conducted with an ovine intrauterine growth restriction (IUGR) model to test the hypothesis that dietary rumen-protected l-arginine (RP-Arg) or N-carbamylglutamate (NCG) supplementation in underfed ewes is effective in enhancing fetal growth. Between Days 35 and 110 of pregnancy, 32 multiparous ewes carrying two fetuses were randomly assigned to one of four groups: a control (CG) group (n=8; 100% National Research Council (NRC) requirements for pregnant sheep), a nutrient-restricted (RG) group (n=8; fed 50% NRC requirements, and two treatment (ARG and NCG) groups (n=8 in each group; fed 50% NRC requirements supplemented with 20gday-1 RP-Arg or 5gday-1 NCG. All ewes were killed on Day 110 of pregnancy to determine fetal weight and fetal organ weights, and metabolites and hormones in fetal plasma, amino acid concentrations in the fetal liver and longissimus dorsi muscle, and expression of mRNAs in the somatotropic axis. Maternal and fetal bodyweight and the weight of most fetal organs expressed as a percentage of bodyweight increased in response to ARG and NCG compared with values for fetuses from RG ewes. Fetal plasma concentrations of insulin, insulin-like growth factor 1, total amino acids, lactate, thyroxine, and the thyroxine/tri-iodothyronine ratio were lower in fetuses from RG ewes compared with the other treatment groups, but concentrations of growth hormone, non-esterified fatty acids, and total cholesterol were greater in fetuses from RG ewes. Maternal RP-Arg or NCG supplementation increased concentrations of amino acids in fetal tissues and expression of mRNAs for somatotropic axis proteins in fetuses from RG ewes. These findings suggest that maternal RP-Arg and NCG supplementation of underfed ewes decreases fetal IUGR by improving metabolic homeostasis of fetal endocrinology, increasing the availability of amino acids in the fetal liver and longissimus dorsi muscle and affecting the expression of somatotropic axis genes.

Effects of dietary N-carbamylglutamate supplementation on growth performance, tissue development and blood parameters of yellow-feather broilers

The effects of N-carbamylglutamate (NCG) on the growth performance, tissue development, and blood parameters of broilers are unknown. In this study, 2 linked experiments were conducted to investigate the effects of 4 graded dietary levels and 3 dietary stages of NCG in a Chinese indigenous yellow-feather broiler breed during 2 growth phases: 1 to 18 d and 19 to 36 d. The dietary levels of NCG were 0.05%, 0.10%, 0.15%, and 0.20%, and dietary stages were designed to add NCG during the starter stage or grower stage or throughout the experimental period. At the age of 18 d, graded doses of NCG from 0.05 to 0.20% in the diet produced quadratic (P < 0.05) positive responses in body weight, width of intermuscular fat cingulum, liver weight, serum blood urea nitrogen, and serum low-density lipoprotein as well as linear (P < 0.05) positive responses in albumin serum concentration. The average feed per gain and mortality were unaffected by dietary NCG levels. Among 3 dietary treatments, only NCG dietary treatments throughout the experimental period improved the body weight and daily weight gain linearly (P < 0.05). The daily weight gain under the 3 dietary treatments used indicated that the most fitting dose is 0.1% NCG among the 4 dietary levels of NCG (P < 0.05). At this dose, muscle weight increased, whereas subcutaneous adipose as well as the serum contents of uric acid, triglyceride, and albumin decreased. Considering the growth performance and tissue development under the conditions used in this study, the best-fit model for NCG requirements of Chinese yellow-feather broilers was estimated from regression analysis to be 0.09 to 0.12% dietary NCG treatments during the grower stage. The modified blood parameters indicated that NCG dietary effects on broiler growth may be accompanied by modified homeostasis of arginine metabolism, lipid deposition, protein synthesis, and immune response.

Effectiveness of citrulline and N-carbamoyl glutamate as arginine precursors on reproductive performance in mammals: A systematic review

The use of functional nutrients has been proposed to reduce the occurrence of intrauterine growth retardation in animals at birth in several mammalian species. The objective of this study was to verify the effectiveness of citrulline and N-carbamylglutamate (NCG) dietary supplementation as arginine precursors for mammalian species, and the effects on fetal development through a systematic review. The search for studies was performed during August 2018 in the PubMed, ISI Web of Science, Science Direct, and Scopus databases. The literature search was conducted using "arginine precursor", "citrulline", or "N-carbamylglutamate" as keywords, combined with "gestation", "pregnancy", "fetus", "newborn", or "reproduction". Studies in which arginine precursors were evaluated in gestating mammals and their effects on parameters related to the intrauterine development of the conceptus were selected. Of 1,379 articles, 18 were selected, primarily based on the title and the abstract. Supplementation with NCG (0.5 g to 2 g/kg of feed) increased maternal plasma arginine concentrations in all studies that evaluated this variable. Fetal number increased in 55.56% of the studies that evaluated it, and fetal weight increased in the majority (62.5%) of the studies evaluating this variable. By supplementing citrulline, only fetal weight was improved, with an increase in maternal plasma arginine in 40% of the studies. In conclusion, N-carbamoyl glutamate seems to be an arginine precursor more effective than L-citrulline during gestation; however, both precursors, beside L-Arginine, should be evaluated in similar conditions to confirm the existence of specific particularities such as periods and levels of supplementation, which need to be considered for different species of animals. The supplementation of NCG increases arginine concentrations in maternal plasma, thus improving mammalian reproductive efficiency and fetal development, mainly by promoting higher birth weight.