Glycine has the greatest rate of deposition in whole-body proteins among all amino acids in neonates, but its provision from sow’s milk meets only 20% of the requirement of suckling piglets. The results of our recent studies indicate that piglets with intrauterine growth restriction (IUGR) have a reduced ability to synthesize glycine. The present study determined the role of glycine in the growth of sow-reared IUGR piglets. In Experiment 1, 56 newborn piglets (postnatal day 0) with a low birth weight (<1.10 kg) were selected from 14 litters, providing 4 IUGR piglets/litter that were allotted randomly into one of four treatment groups (14 piglets/group). Piglets received oral administration of either 0, 0.1, 0.2 or 0.4 g glycine/kg body weight (BW) twice daily (i.e., 0, 0.2, 0.4 or 0.8 g glycine/kg BW/day) between 0 and 14 days of age. L-Alanine was used as the isonitrogenous control. The BWs of all piglets were recorded each week during the experiment. Two weeks after the initiation of glycine supplementation, blood and tissue samples were collected for biochemical analyses. In Experiment 2, rates of muscle protein synthesis in tissues were determined on day 14 using the 3H-phenylalanine flooding dose technique. Compared with piglets in the control group, oral administration of 0.2, 0.4 and 0.8 g glycine/kg BW/day did not affect their milk intake (p > 0.05) but increased (p < 0.05) concentrations of glycine in plasma by 1.52-, 1.94-, and 2.34-fold, respectively, and body weight by 20%, 37%, and 34%, respectively. The dose of 0.4 g glycine/kg BW/day was the most cost-effective. Consistent with its growth-promoting effect, glycine supplementation stimulated (p < 0.05) the phosphorylation of mechanistic target of rapamycin (MTOR), eukaryotic initiation factor 4E binding protein 1 (4E-BP1), and ribosomal protein S6 kinase beta-1 (p70S6K) as well as protein synthesis in skeletal muscle, compared with the control group. Collectively, oral administration of glycine activated the MTOR signaling pathway in skeletal muscle and enhanced the growth performance of IUGR piglets. These results indicate that endogenous synthesis of glycine is inadequate to meet the needs of IUGR piglets during the suckling period and that oral supplementation with glycine to these compromized neonates can improve their growth performance.

Background The creatine-creatine kinase-phosphocreatine(Cr-CK-PCr) system maintains intracellular ratios of ATP/ADP for support of cellular functions and has been characterized at the placental-uterine interface of rodents, primates, swine and sheep, and thus may support fetal development. This study determined effects of dietary supplementation of creatine(Cr) to gestating gilts on fetal development, the number and ratio of primary and secondary muscle fibers, and on protein expression in endometrium and fetal biceps-femoris muscle, respectively in fetal pigs on d 60 and d 90 of gestation.Methods Reproductively mature gilts were synchronized to estrus using Matrix, observed for estrus(d 0), and artificially inseminated 12 h and 36 h later. Gilts were individually housed and fed 0.86 kg of 14% crude protein diet twice daily that meets nutritional requirements for pregnant gilts. Gilts were assigned to either basal diet control(CON) group, or Cr supplemented group(provided 30 g Cr monohydrate daily) from d 10 to either d 60 or d 90 of gestation. Gilts were euthanized and hysterectomized on either d 60 or d 90 of gestation. These protocols were completed in two replicates, as gilts were bred in spring and euthanized in summer or bred in fall and euthanized in winter(n = 20 gilts/replicate). Litter size, crown-rump length, sex, and fetal weight was recorded. Three female and male fetuses closest to mean litter weight were selected to assess effects of treatment on weight of fetal brain, kidney, liver, spleen, and biceps-femoris muscle. Data were analyzed to determine effects of treatment, days of gestation, replicate, and sex on litter size, fetal measurements, and incidence of intrauterine growth restriction.Results Dietary Cr supplementation increased fetal brain weight to body weight ratios on d 90 of gestation(P < 0.05) and fetal kidney weight to body weight ratios on d 60 of gestation(P < 0.01), while days of gestation had significant effect on expression of mitochondrial CK isoform in gilt endometria(P < 0.05).Conclusions Results suggest that dietary supplementation of Cr in gestating gilts enhanced development of select fetal organs and contribute to understanding roles of the Cr-CK-PCr system in pregnancy.

Glycine has the greatest rate of deposition in whole-body proteins among all amino acids in neonates, but is remarkably deficient in the milk of mammals including pigs, humans, and cows. Results of our recent studies indicate that piglets with intrauterine growth restriction (IUGR) have a reduced ability to synthesize glycine. The present study determined the role of dietary glycine in the growth of sow-reared IUGR piglets. In Experiment 1, 56 newborn piglets (postnatal day 0) with low birth weights (< 1.10 kg) were from 14 litters, providing 4 IUGR piglets/litter that were allotted randomly into one of four treatment groups (14 piglets/group). Piglets received oral administration of either 0, 0.1, 0.2 or 0.4 g glycine/kg body weight twice daily (i.e., 0, 0.2, 0.4 or 0.8 g glycine/kg body weight/d) between 0 and 14 d of age. L-Alanine was used as the isonitrogenous control. The body weights of all piglets were recorded each week during the experiment. Two weeks after the initiation of glycine supplementation, blood and tissue samples were collected for biochemical analyses. In Experiment 2, rates of protein synthesis in tissues were determined using the 3H-phenylalanine flooding dose technique. Results were analyzed statistically using one-way or two-way ANOVA. The consumption of milk by IUGR piglets measured at 13 d of age was 236 ± 15, 228 ± 12, 244 ± 18, and 240 ± 16 mL/kg BW/d, respectively, in the 0, 0.2, 0.4, and 0.8 g glycine/kg BW/day groups (P > 0.05). Concentrations of serine in plasma were 18% and 25% greater (P < 0.05) in piglets receiving oral administration of 0.4 and 0.8 g glycine/kg BW/day, respectively, than those in the control group. Compared with piglets in the control group, oral administration of 0.2, 0.4 and 0.8 g glycine/kg body weight/d increased (P < 0.05) concentrations of glycine in plasma by 1.52-, 1.94-, and 2.34-fold, respectively, as well as body weight by 20%, 37%, and 34%, respectively. Consistent with its growth-promoting effect, glycine supplementation increased (P < 0.05) the phosphorylation of mechanistic target of rapamycin (MTOR), eukaryotic initiation factor 4E binding protein 1 (4E-BP1), and ribosomal protein S6 kinase beta-1 (S6K1) by 330%, 170%, and 180%, respectively, and the fractional rate of protein synthesis by 16%, in longissimus lumborum muscle, compared with the control group. Collectively, oral administration of glycine activated the MTOR signaling pathway in skeletal muscle and promoted the growth performance of IUGR piglets. These results indicate that the endogenous synthesis of glycine is inadequate to meet the metabolic needs of IUGR piglets during the suckling period. (Supported by Agriculture and Food Research Initiative Competitive Grant 2014-67015-21770 from the USDA National Institute of Food and Agriculture)

Abstract:Tissue non-specific alkaline phosphatase (TNSALP) regulates postnatal phosphate homeostasis, but its role in utero-placental phosphate availability remains poorly understood. Gilts were bred and hysterectomized on Day 60 or Day 90 of gestation (n = 6/day). Phosphate was less abundant in allantoic and amniotic fluids on Day 90 compared to Day 60. TNSALP protein was immunolocalized, and enzymatic activity was quantified and localized in endometrial and chorioallantois tissues. Day had no effect on TNSALP activity in the chorioallantois. In contrast, endometrial TNSALP activity was lower on Day 90 compared to Day 60. Phosphate abundance in allantoic fluid correlated positively with endometrial TNSALP activity on Day 60 but not Day 90. TNSALP protein was abundantly expressed in the endometrium and chorioallantois on both days investigated, with localization to the endometrial, chorionic, and areolar epithelia, as well as stromal cells and endothelium. TNSALP activity was detected in the endothelium of the blood vessels in both the endometrium and chorioallantois, and on the basal surface of the endometrial glands on Day 60 but not Day 90. The endometrial stratum compactum stroma had strong TNSALP activity on Day 60. Weak TNSALP activity was present in the areolar epithelium, with a modest increase in activity on Day 90 compared to Day 60. TNSALP activity was present in the columnar chorionic epithelial cells, with an apparent decrease in activity in the chorioallantois on Day 90 compared to Day 60. These data reveal spatiotemporal changes in TNSALP localization and activity, suggesting its involvement in regulating phosphate availability at the utero-placental interface in swine. Lay Summary:Phosphate is an essential nutrient for fetal growth, but how it is managed during pregnancy is not fully understood. This study explored the role of an enzyme called tissue non-specific alkaline phosphatase (TNSALP) in regulating phosphate availability in the uterus and placenta in pigs in mid- and late pregnancy. Phosphate levels decreased in the fluids surrounding the fetus in late pregnancy. TNSALP was present in the uterus and placenta, and the amount of the enzyme varied depending on the tissue and stage of pregnancy and correlated with changes in phosphate levels. These findings suggest that TNSALP plays a key role in managing phosphate transport from the mother to the fetus in pregnancy to support fetal development.

The creatine (Cr) biosynthesis pathway buffers adenosine triphosphate in metabolically active tissues. We investigated whether sex of fetus and day of gestation influence Cr in endometrial and conceptus tissues from gilts on days 60 and 90 (n = 6 gilts/day) of gestation. Uterine and conceptus tissues associated with one male and one female fetus from each gilt were analyzed for creatine, messenger RNAs (mRNAs), and proteins for Cr biosynthesis. Total Cr decreased in amniotic fluid but increased in allantoic fluid between days 60 and 90 of gestation for male (P < 0.05) but not for female fetuses (P > 0.05). Endometrial expression of creatine kinase, muscle (CKM), creatine kinase mitochondrial type 1 (CKMT1), and solute carrier family 6, member 8 (SLC6A8) mRNAs increased (P < 0.05) between days 60 and 90 only for female fetuses. On day 60, expression of creatine kinase, brain (CKB) and CKMT1 mRNAs was greater (P < 0.05) for placentae of female than male fetuses. Livers of male fetuses had greater expression of arginine:glycine amidinotransferase (AGAT) and CKB than for females on day 60, while kidneys of female fetuses had greater expression of guanidinoacetate-N-methyltransferase (GAMT) than male fetuses on day 90 (P < 0.05). Localization of GAMT, CKB, CKMT1, and SLC6A8 proteins to uterine and chorionic epithelium was not influenced by gestational age or fetal sex. Arginine-glycine amidinotransferase localized to fetal kidneys and appeared greater on day 90 than on day 60 in both sexes. Thus, expression of the creatine-creatine kinase-phosphocreatine system at the uterine-conceptus interface is affected by gestational age and fetal sex to influence energy homeostasis in pigs.

Introduction:L-Glutamate is a conditionally essential amino acid, meaning it can become essential under specific conditions, like stress or disease. It is an abundant intracellular amino acid crucial in immune responses. Supplementation of feed with key amino acids, such as glutamate, can optimize growth and have other health benefits for production animals. Most research on dietary amino acid supplementation has focused on mammalian models, thus this research turned to hybrid striped bass, a teleost fish of growing importance to the aquaculture industry. The study investigated the effects of dietary supplementation with 0% or 5% glutamate in hybrid striped bass on intestinal mucosal immunity. Methods:The basal purified diet contained crystalline amino acids, including 3% L-glutamate. After an 8-week period of dietary supplementation with 5% glutamate followed by lipopolysaccharide stimulation, the intestinal mucosa was analyzed at the cellular and molecular levels to compare with the head kidney to assess potential changes in immune reactivity. Results:One week after lipopolysaccharide stimulation, glutamate supplementation enhanced (P < 0.05) the whole-body growth of fish without lipopolysaccharide challenge, total respiratory burst (the sum of O2 - and H2O2 production) in head kidney leukocytes, the net production of H2O2 in intestinal mucosal leukocytes, and upregulation of expression of mRNAs for IL-1β, TNF-α, and IgT in the gut mucosa. Discussion:Dietary supplementation with 5% L-glutamate may modulate intestinal mucosal immunity and improve growth in HSB to enhance disease resistance. Further research is needed to clarify the mechanism and cost-effective application.

Background Meat goat production is a worldwide industry with products such as meat,milk,soap,and fiber being produced.There are approximately 2.6 million meat goats in the United States.For breeding female ruminants,early pregnancy loss is estimated to be 30％within the first month of gestation.Extracellular L-citrul line(a precursor to L-arginine)is not degraded by ruminal microbes due to the lack of uptake.L-Arginine and thus L-citrulline,have beneficial impacts on placentation and,subsequently,fetal-placental development and survival.This study aimed to determine the impact of feeding L-citrulline to meat goats during gestation to improve reproductive success.Meat goats were fed either a control(CON)or L-citrulline(CIT)supplemented diet from d 12 to 82 of gestation.Blood samples were collected and sera were subjected to high-performance liquid chromatography analyses to quantify the abundance of amino acids.Pregnancy rates were determined on d 30,61,and 90 of gestation,and litter weight,individual birth weights,and 90 d adjusted weaning weights were collected. Results The concentrations of citrulline,ornithine,and arginine were greater in CIT does compared to CON does,but there was no difference in pregnancy rates between CON and CIT does.Birth weight was greater for male kids born as singles when compared to females,but this phenotype was not observed for kids born as twins or triplets.Further,males born to CON does had greater 90 d adjusted weaning weights than females,but this was not observed in the CIT group.Female kids born to CON and CIT Boer goats had heavier 90 d adjusted weaning weights than those born to Spanish or F1 Boer-Spanish does. Conclusion This study provides proof of concept that feeding dietary L-citrulline increases concentrations of citrul-line and arginine in blood of gestating meat goats.However,further studies are needed to understand the cellular mechanisms impacted by feeding this supplement.Regardless,this study demonstrated that feeding L-citrulline has the potential to increase reproductive performance in gestating ruminants.

Species have different strategies for implantation and placentation. Much can be learned about general molecular and cellular biology through the examination and comparison of these differences. To varying degrees, implantation in all species includes alterations in epithelial polarity, the transformation of the endometrial stroma, the differentiation of the trophoblast, cell-to-cell and tissue-to-tissue signaling through hormones, cytokines, and extracellular vesicles, and the alteration of the maternal immune system. This review focuses on implantation in pigs, sheep, and cows. These species share with mice/rats and humans/primates the key events of early embryonic development, pregnancy recognition, and the establishment of functional placentation. However, there are differences between the pregnancies of livestock and other species that make livestock unique biomedical models for the study of pregnancy and cell biology in general. Pig, sheep, and cow conceptuses (embryo/fetus and associated placental membranes) elongate prior to implantation, displaying central implantation, extended periods of conceptus attachment to the uterus, and epitheliochorial (pigs) and synepitheliochorial (sheep and cows) placentation. This review will discuss what is understood about how the trophoblast and extraembryonic endoderm of pig, sheep, and cow conceptuses elongate, and how a major goal of current in vitro models is to achieve conceptus elongation. It will then examine the adhesion cascade for conceptus implantation that initiates early placental development in pigs, sheep, and cows. Finally, it will conclude with a brief overview of early placental development in pigs, sheep, and cows, with a listing of some important “omics” studies that have been published.

In brief:Phosphate plays a critical role in conceptus development, yet the mechanisms regulating utero-placental availability remain underinvestigated. This research characterized the spatiotemporal expression and endocrine regulation of XPR1, a phosphate exporter, in ovine utero-placental tissues, suggesting a potential role of XPR1 in the regulation of utero-placental phosphate availability. Abstract:Phosphate is an essential regulator of conceptus development, but there is limited understanding of mechanisms regulating phosphate availability in utero-placental tissues. These experiments characterized the expression of xenotropic and polytropic retrovirus receptor 1 (XPR1), a phosphate exporter, in ovine utero-placental tissues. In Experiment 1, ewes were hysterectomized on day 1, 9, or 14 of the estrous cycle or day 30, 50, 70, 110, or 125 of pregnancy. Day of the estrous cycle did not affect XPR1 mRNA expression or protein localization. Expression of XPR1 mRNA decreased with day of gestation in placentomes, while XPR1 protein was detectable in uterine epithelia, blood vessels, endometrial stromal cells, myometrium, caruncular stroma, and syncytium of the placentome. In Experiment 2, ewes received daily injections of either corn oil vehicle (CO) or 25 mg progesterone (P4) in vehicle for the first 8 days of pregnancy and were hysterectomized on either day 9, 12, or 125. Endometrial stroma from P4-treated ewes had greater XPR1 immunoreactivity than CO-treated ewes on day 9. On day 125, endometria from P4-treated ewes had decreased expression of XPR1 mRNA compared to CO-treated ewes. Greater XPR1 protein immunoreactivity was present in uterine epithelia and stratum compactum stroma of P4-treated than CO-treated ewes. P4-treated ewes with a singleton fetus tended to have greater expression of XPR1 mRNA in placentomes than CO-treated ewes with a singleton fetus. Collectively, these results suggest a potential role of XPR1 in the regulation of phosphate availability in utero-placental tissues in ruminants.

Low fertility limits reproductive efficiency in cattle. This study was conducted with multiparous Brangus cows receiving dietary supplementation with or without L-citrulline [Cit; an immediate precursor of L-arginine (Arg)]. During the entire experimental period, cows grazed green pasture and had free access to drinking water and mineral blocks. One hundred and seven (107) cows were assigned randomly to one of three treatment groups: dried distillers grains with solubles (DDGS) without Cit supplement (n = 36); DDGS top-dressed with rumen-protected Cit product (RPAA; n = 36); or unprotected Cit product (RUAA; n = 35). After 2 months of lactation, all cows were synchronized to estrus and were bred once via artificial insemination. From Day 1 to Day 60 of gestation, cows were individually fed once daily 0.84 kg of a supplement (DDGS; control), 0.56 kg of DDGS plus 0.28 kg of RUAA (containing 0.07 kg of unencapsulated Cit), or 0.56 kg of DDGS plus 0.28 kg of RPAA (containing 0.07 kg of rumen-protected Cit). The supplemental dose of Cit was equivalent to 0.5% of the estimated daily intake of 14 kg dry matter from pasture. On Days 40 and 60 of gestation, ultrasound was used to determine pregnancy rates. Each pregnant cow had a single conceptus. On Day 60 of gestation, blood samples were obtained from the jugular vein. All cows grazed normally and appeared healthy. Birth rates for live-born calves were 22% and 35% in cows receiving DDGS alone and Cit supplementation, respectively (p < 0.05). The beneficial effect of Cit was associated with increases in concentrations of Cit (+19%), Arg (+20%), ornithine (+19%), proline (+17%), and insulin (+82%) but decreases in concentrations of ammonia (-14%) in maternal plasma (p < 0.05). Thus, dietary supplementation with Cit is a simple, novel, and cost-effective nutritional method to increase the reproductive efficiency of lactating beef cows.

Background Lactational performance depends heavily on age, health, and nutrition. L-Citrulline(Cit) is an effective precursor of L-arginine(Arg), an amino acid that has important roles in synthesis of nitric oxide(NO) and polyamines. Ruminal microbes degrade extracellular Arg; however, extracellular L-citrulline(Cit) is not degraded by ruminal microbes due to lack of uptake and can be fed unencapsulated as a precursor for Arg. As NO is a vasodilator, an increase in blood flow and transport of molecules to mammary tissue may enhance lactational performance and milk composition. Increases in polyamine production may increase milk protein synthesis within mammary tissue, thus increasing milk protein content. This study determined, for the first time, effects of dietary Cit supplementation on milk production and milk composition of Alpine dairy goats.Methods Does were synchronized to estrus and bred to Alpine bucks. Parturition was induced on d 149 of gestation and does were suckled overnight allowing kid(s) to obtain colostrum before being milked 24 h later(d 1 of lactation). Does were assigned to either control(CON, n = 24) or Cit(CIT, n = 23) diets. The isonitrogenous control diet consisted of 97.63% basal diet and 2.37% supplement(1.37% L-alanine and 1.00% soybean hydrogenated oil). The CIT supplemented diet consisted of 97.63% basal diet and 2.37% supplement(0.5% Cit, 0.5% L-glutamine, 1% soybean hydrogenated oil, 0.37% cornstarch). Diets were group fed ad-libitum by treatment group. Blood samples were collected on d 0 and 30 of lactation, milk volumes measured twice daily, and on d 10, 20, and 40 of lactation, milk samples were collected.Results CIT-treated does had greater daily milk production(P < 0.05) and there was an effect of day of lactation on daily milk production(P < 0.0001). Sire had significant effect on daily milk production as well(P < 0.05). Milk compositional analyses revealed Cit supplementation increased solid-non-fat(SNF; P < 0.05) and protein(P < 0.05) content in milk.Conclusions Our novel results indicate that dietary supplementation of Cit fed ad-libitum in Alpine does increased daily milk yield, milk SNF content, and protein content. Supplemental Cit may be a proxy for Arg in goats to enhance lactational performance.

Histotroph is regulated by P4 and paracrine factors and contains amino acids essential for porcine conceptus development. We hypothesized P4 contributes to amino acid transport during pregnancy in pigs. Ovariectomized gilts received daily P4 or corn oil (CO) injections from Days 12 through 39 post-estrus. High-performance liquid chromatography (HPLC) determined increased abundances of amino acids including glycine, in uterine flushings from P4-treated gilts. SLCs transport amino acids across membranes. rtPCR analyses revealed endometrial expression of SLC6A9 mRNA increased during the peri-implantation period of pregnancy. SLC7A8 and SLC38A1 mRNA expression also increased during that period but decreased later in pregnancy. SLC1A4, SLC1A5, and SLC7A10 mRNA expression was greatest later in pregnancy. Immunofluorescence analyses localized SLC6A9, which transports glycine exclusively, to the endometrial luminal epithelium from Day 12 through 25, uterine glandular epithelium throughout gestation, conceptus trophectoderm and endoderm between Days 15 and 20, and chorionic epithelia (CE) of interareolar and areolar CE between Days 40 and 60. Expression in interareolar regions decreased by Day 60 but remained high in the areolae. Expression of SLC6A9 was greater for endometrium from P4-treated than CO-treated pigs. These results illustrate the complexity of, and stage-dependent changes in, expression of amino acid transporters in endometria from pregnant pigs. The results suggest that transport of glycine into the uterine lumen and across the chorioallantois by SLC6A9 may be critical for delivery of this amino acid that is essential for conceptus development.

Neonatal piglets with intrauterine growth restriction (IUGR) exhibit reduced rates of growth and survival. The present study tested the hypothesis that L-arginine supplementation can mitigate this problem. One hundred and twelve (112) IUGR piglets (with a mean birth weight of 0.84 kg) from 28 sows (four IUGR piglets/sow) were assigned randomly into one of four groups. Piglets were nursed by sows and orally administered 0, 0.1, 0.2, or 0.4 g L-arginine (in the form of L-arginine-HCl) per kg body weight (BW) twice daily between 0 and 14 days of age. The total doses of L-arginine were 0, 0.2, 0.4, or 0.8 g/kg BW/day. Appropriate amounts of L-alanine were added to L-arginine solutions so that all groups of piglets received the same amount of nitrogen. Piglets were weighed on days 0, 7, and 14 of age. On day 14, blood samples (5 mL) were obtained from the jugular vein of piglets at 1 h after suckling, and their milk consumption was measured over a 10-h period using the weigh-suckle-weigh technique. Milk intake did not differ (p > 0.05) among the four groups of piglets. Oral administration of 0.4 g L-arginine/kg BW/day increased (p < 0.05) the circulating levels of arginine, creatine, and anabolic hormones (insulin, growth hormone, and insulin-like growth factor-I), but decreased (p < 0.05) plasma concentrations of ammonia and cortisol (a catabolic hormone). Compared to the control group, IUGR piglets administered 0.2 and 0.4 g L-arginine/kg BW/day increased (p < 0.05) weight gain by 19% and 31%, respectively. Growth did not differ (p > 0.05) between the control and 0.8 g L-arginine/kg BW/day groups. The survival rates of IUGR piglets were 50%, 75%, 89%, and 89%, respectively, for the 0, 0.2, 0.4, and 0.8 g L-arginine/kg BW/day groups. Collectively, these results indicate that the growth and survival of IUGR piglets can be improved through L-arginine supplementation.

The hair and skin of domestic cats or dogs account for 2% and 12-24% of their body weight, respectively, depending on breed and age. These connective tissues contain protein as the major constituent and provide the first line of defense against external pathogens and toxins. Maintenance of the skin and hair in smooth and elastic states requires special nutritional support, particularly an adequate provision of amino acids (AAs). Keratin (rich in cysteine, serine and glycine) is the major protein both in the epidermis of the skin and in the hair. Filaggrin [rich in some AAs (e.g., serine, glutamate, glutamine, glycine, arginine, and histidine)] is another physiologically important protein in the epidermis of the skin. Collagen and elastin (rich in glycine and proline plus 4-hydroxyproline) are the predominant proteins in the dermis and hypodermis of the skin. Taurine and 4-hydroxyproline are abundant free AAs in the skin of dogs and cats, and 4-hydroxyproline is also an abundant free AA in their hair. The epidermis of the skin synthesizes melanin (the pigment in the skin and hair) from tyrosine and produces trans-urocanate from histidine. Qualitative requirements for proteinogenic AAs are similar between cats and dogs but not identical. Both animal species require the same AAs to nourish the hair and skin but the amounts differ. Other factors (e.g., breeds, coat color, and age) may affect the requirements of cats or dogs for nutrients. The development of a healthy coat, especially a black coat, as well as healthy skin critically depends on AAs [particularly arginine, glycine, histidine, proline, 4-hydroxyproline, and serine, sulfur AAs (methionine, cysteine, and taurine), phenylalanine, and tyrosine] and creatine. Although there are a myriad of studies on AA nutrition in cats and dogs, there is still much to learn about how each AA affects the growth, development and maintenance of the hair and skin. Animal-sourced foodstuffs (e.g., feather meal and poultry by-product meal) are excellent sources of the AAs that are crucial to maintain the normal structure and health of the skin and hair in dogs and cats.

Domestic dogs (facultative carnivores) and cats (obligate carnivores) have been human companions for at least 12,000 and 9000 years, respectively. These animal species have a relatively short digestive tract but a large stomach volume and share many common features of physiological processes, intestinal microbes, and nutrient metabolism. The taste buds of the canine and feline tongues can distinguish sour, umami, bitter, and salty substances. Dogs, but not cats, possess sweet receptors. alpha-Amylase activity is either absent or very low in canine and feline saliva, and is present at low or substantial levels in the pancreatic secretions of cats or dogs, respectively. Thus, unlike cats, dogs have adapted to high-starch rations while also consuming animal-sourced foods. At metabolic levels, both dogs and cats synthesize de novo vitamin C and many amino acids (AAs, such as Ala, Asn, Asp, Glu, Gln, Gly, Pro, and Ser) but have a very limited ability to form vitamin D-3. Compared with dogs, cats have higher requirements for AAs, some B-complex vitamins, and choline; greater rates of gluconeogenesis; a higher capacity to tolerate AA imbalances and antagonism; a more limited ability to synthesize arginine and taurine from glutamine/proline and cysteine, respectively; and a very limited ability to generate polyunsaturated fatty acids (PUFAs) from respective substrates. Unlike dogs, cats cannot convert either beta-carotene into vitamin A or tryptophan into niacin. Dogs can thrive on one large meal daily and select high-fat over low-fat diets, whereas cats eat more frequently during light and dark periods and select high-protein over low-protein diets. There are increasing concerns over the health of skin, hair, bone, and joints (specialized connective tissues containing large amounts of collagen and/or keratin); sarcopenia (age-related losses of skeletal-muscle mass and function); and cognitive function in dogs and cats. Sufficient intakes of proteinogenic AAs and taurine along with vitamins, minerals, and PUFAs are crucial for the normal structures of the skin, hair, bone, and joints, while mitigating sarcopenia and cognitive dysfunction. Although pet owners may have different perceptions about the feeding and management practice of their dogs and cats, the health and well-being of the companion animals critically depend on safe, balanced, and nutritive foods. The new knowledge covered in this volume of Adv Exp Med Biol is essential to guide the formulation of pet foods to improve the growth, development, brain function, reproduction, lactation, and health of the companion animals.

Adult humans generally experience a 0.5-1%/year loss in whole-body skeletal muscle mass and a reduction of muscle strength by 1.5-5%/year beginning at the age of 50 years. This results in sarcopenia (aging-related progressive losses of skeletal muscle mass and strength) that affects 10-16% of adults aged >= 60 years worldwide. Concentrations of some amino acids (AAs) such as branched-chain AAs, arginine, glutamine, glycine, and serine are reduced in the plasma of older than young adults likely due to insufficient protein intake, reduced protein digestibility, and increased AA catabolism by the portal-drained viscera. Acute, short-term, or long-term administration of some of these AAs or a mixture of proteinogenic AAs can enhance blood flow to skeletal muscle, activate the mechanistic target of rapamycin cell signaling pathway for the initiation of muscle protein synthesis, and modulate the metabolic activity of the muscle. In addition, some AA metabolites such as taurine, beta-alanine, carnosine, and creatine have similar physiological effects on improving muscle mass and function in older adults. Long-term adequate intakes of protein and the AA metabolites can aid in mitigating sarcopenia in elderly adults. Appropriate combinations of animal- and plant-sourced foods are most desirable to maintain proper dietary AA balance.

The mechanistic target of rapamycin (mTOR) cell signaling pathway serves as the central mechanism for the regulation of tissue protein synthesis and growth. We recently reported that supplementing 1% glycine to corn- and soybean meal-based diets enhanced growth performance between weaning and market weights in pigs with intrauterine growth restriction (IUGR). Results of recent studies have revealed an important role for glycine in activating mTOR and protein synthesis in C2C12 muscle cells. Therefore, the present study tested the hypothesis that dietary glycine supplementation enhanced the mTOR cell signaling pathway in skeletal muscle and other tissues of IUGR pigs. At weaning (21 d of age), IUGR pigs and litter mates with normal birth weights (NBW) were assigned randomly to one of the two groups: supplementation with either 1% glycine or 1.19% l-alanine (isonitrogenous control) to a corn- and soybean meal-based diet. Tissues were obtained from the pigs within 1 wk after the feeding trial ended at 188 d of age to determine the abundances of total and phosphorylated forms of mTOR and its two major downstream proteins: eukaryotic initiation factor 4E-binding protein-1 (4EBP1) and ribosomal protein S6 kinase-1 (p70S6K). Results showed that IUGR decreased (P < 0.05) the abundances of both total and phosphorylated mTOR, 4EBP1, and p70S6K in the gastrocnemius muscle and jejunum. In the longissimus lumborum muscle of IUGR pigs, the abundances of total mTOR did not differ (P > 0.05) but those for phosphorylated mTOR and both total and phosphorylated 4EBP1 and p70S6K were downregulated (P < 0.05), when compared to NBW pigs. These adverse effects of IUGR in the gastrocnemius muscle, longissimus lumborum muscle, and jejunum were prevented (P < 0.05) by dietary glycine supplementation. Interestingly, the abundances of total or phosphorylated mTOR, 4EBP1, and p70S6K in the liver were not affected (P > 0.05) by IUGR or glycine supplementation. Collectively, our findings indicate that IUGR impaired the mTOR cell signaling pathway in the tissues of pigs and that adequate glycine intake was crucial for maintaining active mTOR-dependent protein synthesis for the growth and development of skeletal muscle.

Endothelial dysfunction, underlying the vascular complications of diabetes and other cardiovascular disorders, may result from uncoupling of endothelial nitric oxide synthase (eNOS) activity due to decreased levels of tetrahydrobiopterin (BH4), a critical co-factor for eNOS. Some clinical trials attempting to deliver exogenous BH4 as a potential therapeutic strategy in vascular disease states have failed due to oxidation of BH4 in the circulation. We sought to develop a means of protecting BH4 from oxidation while delivering it to dysfunctional endothelial cells. Polymeric and solid lipid nanoparticles (NPs) loaded with BH4 were delivered by injection or oral gavage, respectively, to streptozotocin-induced diabetic rats. BH4 was measured in coronary endothelial cells and endothelium-dependent vascular reactivity was assessed in vascular rings. Lymphatic uptake of orally delivered lipid NPs was verified by sampling mesenteric lymph. BH4-loaded polymeric NPs maintained nitric oxide production by cultured endothelial cells under conditions of oxidative stress. BH4-loaded NPs, delivered via injection or ingestion, increased coronary endothelial BH4 concentration and improved endothelium-dependent vasorelaxation in diabetic rats. Pharmacodynamics assessment indicated peak concentration of solid lipid NPs in the systemic bloodstream 6 hours after ingestion, with disappearance noted by 48 hours. These studies support the feasibility of utilizing NPs to deliver BH4 to dysfunctional endothelial cells to increase nitric oxide bioavailability. BH4-loaded NPs could provide an innovative tool to restore redox balance in blood vessels and modulate eNOS-mediated vascular function to reverse or retard vascular disease in diabetes.