Vitamin C

Properties and Metabolism

Vitamin C occurs in two forms, namely L-ascorbic acid (reduced form) and dehydro-L-ascorbic acid (oxidized form). Both forms are biologically active. Only the L-isomer of ascorbic acid has activity, with the D-isomer devoid of function. In foods, the reduced form of vitamin C may reversibly oxidize to the dehydro- form, with dehydroascorbic acid further oxidized to the inactive and irreversible compound of diketogulonic acid. This change takes place readily, and thus vitamin C is very susceptible to destruction through oxidation, a change that is accelerated by heat and light. Reversible oxidation-reduction of ascorbic acid with dehydroascorbic acid is the most important chemical property of vitamin C and the basis for its known physiologic activities and stabilities (Jaffe, 1984). Vitamin C is the least stable and, therefore, most easily destroyed of all vitamins. Ascorbic acid is a white to yellow-tinged crystalline powder. It crystallizes out of water as square or oblong crystals (Illus. 6-1) which are slightly soluble in acetone and lower alcohols. A 0.5% solution of ascorbic acid in water is strongly acid with a pH of 3. The vitamin is more stable in an acid than an alkaline medium. A number of chemical substances, such as air pollutants, industrial toxins, heavy metals and tobacco smoke, as well as several pharmacologically active compounds, among them some antidepressants and diuretics, are antagonistic to vitamin C and can lead to increased requirements for the vitamin. Metabolic need for ascorbic acid is a general one among species, but a dietary need is limited to humans, subhuman primates, guinea pigs, fruit-eating bats, some birds (including the red-vented bulbul and related Passeriformes species), insects, fish (such as coho salmon, rainbow trout, and carp), and perhaps certain reptiles (McDowell, 2000). Under normal conditions, swine can synthesize vitamin C within their body.

Properties and Metabolism

Illustration 6-1

Vitamin C is absorbed in a manner similar to carbohydrates (monosaccharides). Intestinal absorption in vitamin C-dependent animals appears to require a sodium-dependent active transport system (Johnston, 2006). It is assumed that those species that are not susceptible to scurvy do have an absorption mechanism by diffusion (Spencer et al., 1963). Ascorbic acid is readily absorbed when small quantities are ingested, but limited intestinal absorption occurs when excess amounts of ascorbic acid are ingested. Bioavailability of vitamin C in foods is limited, but apparently 80% to 90% appears to be absorbed (Kallner et al., 1977). Site of absorption in the guinea pig is located in the duodenal and proximal small intestine, whereas the rat showed highest absorption in the ileum (Hornig et al., 1984).

In its metabolism ascorbic acid is first converted to dehydroascorbate by a number of enzymes or non-enzymatic processes and is then reduced in cells (Johnston et al., 2007). Absorbed vitamin C readily equilibrates with the body pool of the vitamin. No specific binding proteins for ascorbic acid have been reported, and it is suggested that the vitamin is retained by binding to subcellular structures.

Ascorbic acid is widely distributed throughout the tissues, both in animals capable of synthesizing vitamin C as well as in those dependent on an adequate dietary amount of the vitamin. In experimental animals, highest concentrations of vitamin C are found in pituitary and adrenal glands, with high levels also found in the liver, spleen, brain and pancreas. Vitamin C also tends to localize around healing wounds.

Ascorbic acid is excreted mainly in the urine, with small amounts in sweat and feces. In guinea pigs, rats, and rabbits, CO2 is the major excretory mechanism for vitamin C. Primates do not normally utilize the CO2 catabolic pathway, with the main loss occurring in the urine. Urinary excretion of vitamin C depends on body stores, intake and renal function.


Ascorbic acid has been found to be involved in a number of biochemical processes. The function of vitamin C is related to its reversible oxidation and reduction characteristics. However, the exact role of this vitamin in the living system is not completely understood, since a coenzyme form has not yet been reported. In addition to the relationship of ascorbic acid to hydroxylase enzymes, Franceschi et al., (1992) suggests that vitamin C is required for differentiation of connective tissue such as muscle, cartilage and bone derived from mesenchyme (embryonic cells capable of developing into connective tissue). It is proposed that the collagen matrix produced by ascorbic acid-treated cells provides a permissive environment for tissue-specific gene expression. A common finding in all studies is that vitamin C can alter the expression of multiple genes as cells progress through specific differentiation programs (Ikeda et al., 1997). The most clearly established functional role for vitamin C involves collagen biosynthesis. Beneficial effects result from ascorbic acid in the synthesis of “repair” collagen. Alteration of basement membrane collagen synthesis and its integrity in mucosal epithelium during vitamin C restriction might explain the mechanism by which the capillary fragility is induced in scurvy and also the increased incidences of periodontal disease under vitamin C deprivation (Johnston et al., 2007). Failure of wounds to heal and gum and bone changes resulting from vitamin C undernutrition are direct consequences of reduction of insoluble collagen fibers.

Biochemical and physiological functions of vitamin C have been reviewed (Johnston 2006; Johnston et al., 2007). The functional importance of vitamin C, other than the previously mentioned role in collagen synthesis, includes the following:

  1. Due to the ease with which ascorbic acid can be oxidized and reversibly reduced, it is probable that it plays an important role in reactions involving electron transfer in the cell. Almost all terminal oxidases in plant and animal tissues are capable of directly or indirectly catalyzing the oxidation of L-ascorbic acid. Such enzymes include ascorbic acid oxidase, cytochrome oxidase, phenolase, and peroxidase. In addition, its oxidation is readily included under aerobic conditions by many metal ions and quinones.
  2. Metabolic oxidation of certain amino acids including tyrosine.
  3. Ascorbic acid has a role in metal ion metabolism due to its reducing and chelating properties. It can result in enhanced absorption of minerals from the diet and their mobilization and distribution throughout the body. Ascorbic acid promotes non-heme iron absorption from food (Olivares et al., 1997) and acts by reducing the ferric iron in the acid pH of the stomach and by forming complexes with iron ions that stay in solution at alkaline conditions in the duodenum. Also, a sufficient vitamin C status is a prerequisite for the C-1 hydroxylation of vitamin D3 and conversion of its storage form 25-(OH)D3 to the active form 1,25-(OH)2D3 (Suter, 1990).
  4. Carnitine is synthesized from lysine and methionine and is dependent on two hydroxylases, both containing ferrous iron and L-ascorbic acid. Vitamin C deficiency can reduce the formation of carnitine, which can result in accumulation of triglycerides in blood and physical fatigue and lassitude associated with scurvy (Ha et al., 1994). About 98% of total body carnitine is in muscle. Skeletal and heart muscle carnitine concentrations are reduced by 50% in vitamin C-deficient guinea pigs compared with controls (Johnston, 2006).
  5. Interrelationships of vitamin C to B-vitamins are known as tissue levels and urinary excretion of vitamin C is affected in animals with deficiencies of thiamin, riboflavin, pantothenic acid, folic acid and biotin.
  6. Ascorbic acid is reported to have a stimulating effect on phagocytic activity of leukocytes, function of the reticuloendothelial system and formation of antibodies (Shankar, 2006). As an effective scavenger of reactive oxygen species, ascorbic acid minimizes the oxidative stress associated with the respiratory burst of activated phagocytic leukocytes, thereby functioning to control the inflammation and tissue damage associated with immune responses (Chien et al., 2004). Ascorbic acid levels are very high in phagocytic cells with these cells using free radicals and other highly reactive oxygen containing molecules to help kill pathogens that invade the body. In the process, however, cells and tissues may be damaged by these reactive species. Ascorbic acid helps to protect these cells from oxidative damage (McDowell, 2006).

    Tissue defense mechanisms against free-radical damage generally include vitamin C, vitamin E, and beta-carotene as the major vitamin antioxidant sources. In addition, several metalloenzymes that include glutathione peroxidase (selenium), catalase (iron), and superoxide dismutase (copper zinc and manganese) are also critical in protecting the internal cellular constituents from oxidative damage. The dietary and tissue balance of all these nutrients are important in protecting tissue against free radical damage. Both in vitro and in vivo studies showed that the antioxidant vitamins generally enhance different aspects of cellular and noncellular immunity. The antioxidant function of these vitamins could, at least in part, enhance immunity by maintaining the functional and structural integrity of important immune cells. A compromised immune system will result in reduced animal production efficiency through increased susceptibility to diseases, thereby leading to increased animal morbidity and mortality. In data with rats, vitamin C was required for an adequate immune response in limiting lung pathology after influenza virus infection (Li et al., 2006).
  7. Vitamin C has been demonstrated to be a natural inhibitor of nitrosamines,which are potent carcinogens.
  8. Vitamin C is involved in controlling synthesis of glucocorticoids (corticosteroids) in the adrenal gland. The protective effects of vitamin C (also vitamin E) on health may partially be a result of reducing circulating levels of glucocorticoids (Nockels, 1990). During stress, glucocorticoids, which suppress the immune response, are elevated. Vitamin C reduces adrenal glucocorticoid synthesis, helping to maintain immunocompetence. In addition, ascorbate can regenerate the reduced form of alpha-tocopherol, perhaps accounting for observed sparing effects of these vitamins (Jacob, 1995). In the process of sparing fatty acid oxidation, tocopherol is oxidized to the tocopheryl free radical. Ascorbic acid can donate an electron to the tocopheryl free radical, regenerating the reduced antioxidant form of tocopherol.
  9. Ascorbic acid is found in up to a ten-fold concentration in seminal fluid as compared to blood serum levels. Decreasing levels have caused nonspecific sperm agglutination. In a review of ascorbic acid and fertility, Luck et al., (1995) suggest how three of ascorbic acid’s principal functions, namely its promotion of collagen synthesis, its role in hormone production, and its ability to protect cells from free radicals, may explain its reproductive actions.
  10. Vitamin C has a biological role in keratinocytes. Because skin must provide the first line of defense against environmental free radical attack (e.g., sunburn, skin aging and skin cancer), it has developed a complex antioxidant network that includes enzymatic and non-enzymatic components. The epidermis is composed of several layers of keratinocytes supplied with enzymes (superoxide dismutase, catalase, thioredoxin reductase, and glutathione reductase) and low-molecular-weight antioxidant molecules (tocopherol, glutathione, and ascorbic acid) (Podda and Grundmann-Kollmann, 2001).

In keratinocytes, vitamin C contributes to counteract oxidative stress via transcriptional and post-translational mechanisms. Vitamin C can: 1) act directly by scavenging, reactive oxygen species (ROS) generated by stressors; 2) prevent ROS-mediated cell damage by modulating gene expression; 3) regulate keratinocyte differentiation maintaining a balanced redox state; and 4) promote cell cycle arrest and apoptosis in response to DNA damage (Cataniet al., 2005).


A wide variety of plant and animal species can synthesize vitamin C from carbohydrate precursors including glucose and galactose. Ascorbic acid is synthesized by tissues of mammals with the exception of primates (including humans) and guinea pigs. Early researchers (Grollman and Lehninger, 1957) described the synthesis of ascorbic acid in different animal species. The missing step in the pathway of ascorbic acid biosynthesis in all vitamin C-dependent species has been traced to inability to convert L-gulono-gamma-lactone to 2-keto-L-gulonate, which is transformed by spontaneous isomerization into its tautomeric form, L-ascorbic acid. Dietary vitamin C-dependent species, therefore, lack the enzyme L-gulono-gamma-lactone oxidase (GLO). In swine, the GLO activity is dependent on age (Ching and Mahan, 1998). Results from studies with swine suggest that more ascorbic acid was transferred from the dam to the fetuses as pregnancy advanced, possibly suppressing fetal GLO activity (Ching et al., 2001). Thus, fetal liver GLO activity was the primary source of ascorbic acid during early fetal development, but more fetal ascorbic acid was transferred from the dam during later pregnancy. Domestic animals such as swine, poultry, ruminants, horses, dogs and cats have the ability to biosynthesize vitamin C within their body. However, Jensen et al. (1983) observed that the ability to synthesize vitamin C in pigs is genetically affected. Likewise, Palludan and Wegger (1988) reported large differences in ascorbic acid content in tissues and fluids between normal pigs compared to a mutant strain of pigs that was unable to synthesize ascorbic acid. There is no microbial synthesis of the vitamin in the intestine (Miller and Kornegay, 1983). In general, research studies have shown that healthy animals under ordinary conditions do not respond to supplemental vitamin C and hence there is no recommended requirement established by the NRC (1998) or the Agricultural Research Council (ARC, 1981). However, Marks (1975) proposed vitamin C requirements of 300 mg per kg (136 mg per lb) for starting pigs and 150 mg per kg (68 mg per lb) for finishing pigs. Recently, Mahan et al. (1994) and de Rodas et al. (1998) respectively, have reported that 50 and 75 ppm of dietary vitamin C from a stable source improved the performance of pigs during the first 14 days postweaning.


The main sources of vitamin C are fruits and vegetables but some foods of animal origin contain more than traces of the vitamin. Vitamin C occurs in significant quantities in animal organs, such as liver and kidney, but in only small quantities in muscle. Vitamin C is very low in the predominant feedstuffs used for swine (i.e., grains and plant protein supplements). Post-harvest storage values vary with time, temperature, damage and enzyme content (Zee et al., 1991).

L-ascorbic acid is the most important of the several compounds that have vitamin C activity. Ascorbic acid is commercially available in its pure crystalline form and various coated products such as 50% fat-coated and 97.5% ethylcellulose-coated. The more soluble sodium salt of ascorbic acid (sodium ascorbate) is also commercially available. Various derivatives of ascorbic acid, which are more stable than the parent compound, have been shown to provide antiscorbutic activity. These include L-ascorbate-2-sulfate, L-ascorbyl-2-monophosphate, magnesium-L-ascorbyl-2-phosphate, and L-ascorbyl-2-polyphosphate. When providing supplemental ascorbic acid, it is advisable to use a stabilized form. A coating of ascorbic acid crystals with ethylcellulose is a suitable stabilization method. In storage experiments, ascorbic acid protected in this manner was found to be four times more stable than untreated ascorbic acid crystals (Kolb, 1984).

Adams (1982) reported that coated (ethylcellulose) ascorbic acid showed higher retention after processing than the crystalline form, 84% versus 48%. Retention of ascorbic acid in mash feed was fairly good, but with elevated storage time and temperature, stability was poor in crumbled feeds. Although retention of vitamin C activity in feed containing the ethylcellulose-coated product was low, it was 19% to 32% better than that of the crystalline form.

Through modern technological advances, a form of ascorbic acid is currently being marketed as a phosphate ester, which is stable to heat processing and storage conditions. The new product, called L-ascorbyl-2-monophosphate (Rovimix Stay-C 35®), contains 35 percent ascorbic acid. The phosphate ester allows the ascorbic acid to withstand heat processing. When entering the digestive tract of swine, the phosphate ester is cleaved off and the ascorbic acid is available for adsorption. Crystalline L-ascorbic acid or L-ascorbyl-2-polyphosphate were of similar bioavailability for broiler chicks (Pardue et al., 1993). Magnesium-L-ascorbyl-2-phosphate is a stable form of vitamin C that was shown to be available in swine diets (Mahan et al., 1994).


According to Zintzen (1975) the signs of vitamin C deficiency in swine include weakness, fatigue, dyspnea, bone pain and hemorrhages of the skin, musculature, adipose tissue and certain organs. Schwager and Schulze (1998) suggested that ascorbic acid is involved in osteoblast formation, matrix mineralization and bone resorption in pigs. In research with a relatively small number of pigs conducted by Grondalen and Hansen (1981), there was a tendency for less severity of lesions in the elbow joint, distal epiphysial ulna plate or medial femur condyle in pigs that received vitamin C supplementation versus control pigs. Ascorbic acid appears to play a prominent role in collagen synthesis related to the hydroxylation of proline and lysine intracellularly during the formation of tropocollagen. Therefore, some of the effects of vitamin C deficiency are due to collagen failing to crosslink properly, due to the lack of hydroxyproline and hydroxylysine.A specific clinical leg-weakness syndrome in growing pigs manifests itself mainly as crooked and (or) deviated forelegs. These signs are indicated by contracted flexor tendons and weak joint ligaments, which become apparent in pigs weighing 30 to 45 kg (66 to 100 lbs) and seem to indicate an impaired development in growing loaded connective tissues (Nielsen and Vinther, 1984). Vitamin C administered to boars at 500 mg per kg (227 mg per lb) of diet during the growing period, from 39 to 105 kg (86 to 230 lbs) body weight, resulted in straightness of front legs compared to controls (Cleveland et al., 1987a). However, Strittmatter (1977) and Strittmatter et al. (1978) were unable to detect an influence of high levels of dietary ascorbic acid on growth or the severity and incidence of osteochondrosis in pigs. Additional data by Pointillart et al. (1997) also indicated that high intakes of ascorbic acid have no positive effects on bone metabolism and bone characteristics in pigs. However, in a separate report, Denis et al. (1997) indicated that high levels of vitamin C had deleterious effects on trabecular bone formation in young pigs but did not alter the overall bone mass.

According to Chatterjee (1967), degeneration of the ovaries and testes occurs in guinea pigs on an ascorbic acid-free diet, but the effects are associated with general inanition. There is evidence for reduced testosterone synthesis by Leydig cells of the testes of vitamin C-deficient male guinea pigs. The precise role of ascorbic acid in sex steroid biosynthesis has not been established.

In females, there are considerable demands for collagen synthesis and degradation during pregnancy as uterine growth, placental development and fetal development all depend on rapid increases in connective tissue components, of which ascorbic acid plays a critical role. Brown et al. (1970; 1971) evaluated the influence of the level of energy and ascorbate supplementation on hydroxyproline excretion in swine. Their data suggested that when energy is limited, capacity of swine to synthesize ascorbic acid is limited and supplementary ascorbate might increase polymerization of precursor collagen into stable forms. In a study with pregnant sows, Wegger (1994) reported that maternal ascorbic acid deficiency impairs both mineralization in fetal bone and formation of normal osteoid. Defective collagen synthesis and decreased proteoglycan synthesis were suggested to be involved. Wegger and Palludan (1994) provided a more detailed description of the skeletal abnormalities during fetal development in swine resulting from maternal vitamin C deficiency.

Ascorbic acid is also known to enhance absorption of iron from the intestine (Volker et al., 1984). In hematopoiesis, ascorbic acid facilitates the transfer of iron from transferrin (a plasma protein) to ferritin (an organ protein), which serves in the storage of iron in bone marrow, spleen and liver. Ascorbic acid deficiency disrupts this transport of iron between blood plasma and storage organs. In reproductive tissues of the sow, the transfer of iron from uteroferrin to transferrin (Buhi, 1981) is likewise facilitated by ascorbic acid. Gipp et al. (1974) reported dietary ascorbic acid supplementation increased the plasma iron level, the degree of saturation of plasma transferrin and the rate of removal from plasma and uptake by red blood cells of iron-59. These authors suggested that ascorbic acid may help overcome iron deficiency induced by high dietary copper either through interfering with copper absorption or increasing absorption and utilization of iron. Voelker and Carlton (1969) had reported previously that excess dietary ascorbic acid had adverse effects on absorption, transport and excretion of copper in miniature swine. Perks and Miller (1996) added ascorbic acid to iron-fortified cow’s milk and were unable to detect a long-term effect of ascorbic acid on iron absorption when the fortified milk was supplied to piglets.

Uteroferrin is a purple, progesterone-induced glycoprotein secreted by the uterine endometrial epithelium of both the sow and mare. It transports iron to the developing conceptus (Roberts and Bazer, 1980). Presumably, this is achieved by the ascorbic acid acting as a chelator to transfer iron from uteroferrin to transferrin. Transferrin would then transfer iron to cells of the hematopoietic system of the liver, spleen and bone marrow to meet the need for hemoglobin synthesis and erythrocyte development. This process begins around day 14 of pregnancy as blood islets form in the yolk sac endoderm and continues until near the end of pregnancy when the hematopoietic centers reside principally in bone marrow.

The ascorbic acid content in the sow’s uterus increases during early pregnancy in association with essentially a doubling in uterine length and a significant increase in uterine collagen content (Renegar et al., 1981). The placental membranes and fetuses are also rich in collagen, the synthesis of which is dependent upon vitamin C.

The possible role of ascorbic acid in steroid metabolism within the pregnant uterus is not known. However, decreased cholesterol content of the adrenal gland is characteristic of ascorbic acid-deficient guinea pigs and would reduce substrate availability for synthesis of sex steroids (Chatterjee, 1967). The interconversion of NADPH2 and NADPH can be influenced by the electron transfer from ascorbic acid to dehydroascorbic acid. The production of reducing equivalents (NADPH2) is required for numerous hydroxylation reactions in sex steroid biosynthesis. The establishment and maintenance of pregnancy in all farm animals is dependent upon maintenance of a corpus luteum that produces progesterone and, in some species, estrogen production by the placenta. Since adequate ascorbic acid concentrations in tissue may be essential for normal sex steroid metabolism by ovarian and fetal-placental tissue, vitamin C would appear to be essential to the reproductive process. Petroff et al. (1996) measured the levels of total ascorbate and oxidized ascorbate in ovarian stroma, follicles and corpora lutea throughout the estrus cycle and during pregnancy. They reported that periods of maximal luteal and follicular function are associated with elevated concentrations of total ascorbate within these tissues. In addition, aging of the corpora lutea was associated with a high partitioning of reduced ascorbate. Petroff et al. (1996) demonstrated that prostaglandin (PGF2) depletes the porcine corpus luteum of vitamin C by inducing secretion of the vitamin into the bloodstream. Thus, these findings support the hypothesis that vitamin C depletion contributes to the demise of the porcine corpus luteum.

Ivos et al. (1971) reported an inverse relationship between ambient temperature and conception rate in sows (Figure 6-1). Additionally, these authors reported that average conception rate in sows increased when boars were supplemented with either 1 or 2 gm daily of ascorbic acid compared to controls. Lin et al. (1985) observed increased sperm concentration per ejaculate in heat-stressed working boars that received 300 mg ascorbic acid per day as compared to unsupplemented boars. Boars that received the supplemental ascorbic acid also had fewer abnormal sperm cells per ejaculate. Using a Danish mutant strain of pigs that is unable to synthesize ascorbic acid—Osteogenic Disorder (OD) pigs—Palludan and Wegger (1988) investigated the influence of ascorbic acid status on boar performance. Boars from the OD line had histologic anomalies in the spermatogenic epithelium.

Dvorak and Podany (1971) indicated that high ascorbic acid content of boar testes is related to the optimum development of the gonad. Healthy, fertile boar testis averaged 0.4 mg ascorbic acid per g, which is greater than the ascorbic acid concentration in liver. Total ascorbic acid content of testis decreases to about 250 mg in adult life (Dvorak and Podany, 1966). Dvorak (1984) reported that the ascorbic acid concentration in boar semen was higher than the concentration found in blood serum. However, the concentration of ascorbic acid is affected by accessory gland secretion. Dvorak (1984) indicated that the high ascorbic acid level of the male gonadal glands is related to reproductive function. This applies also to accessory glands as evidenced by the fact that ascorbic acid concentration of these tissues and their secretions were reduced by half one month after castration (Dvorak and Podany, 1971). The role of ascorbic acid in these processes is likely associated with the production of male reproductive cells. Ascorbic acid’s high concentration in semen is a physiological manifestation of sexual activity of the boar and, therefore, a desirable characteristic. Disease conditions have been found to affect vitamin C metabolism. Vitamin C is able to protect tissues by enhancing humoral and cellular immune responses in disease (Nockels, 1988). With a vitamin C deficiency, impaired chemotaxis in macrophages and depressed T-lymphocyte response have been reported (Beisel, 1982). Mozalene et al. (1991) reported that dietary vitamin C had a normalizing effect in pigs on the pathologic reaction induced by infection with T. suis eggs. Their conclusion was based on ceruloplasmin levels, which are indicative of the degree of inflammatory response and changed immunological reactivity of the host.

Swine nutritionists have generally formulated diets without vitamin C because the young pig can synthesize ascorbic acid within a week of birth as demonstrated by Braude et al. (1950), and both sow colostrum and milk provide a plentiful source of the vitamin to the nursing pig (Wegger and Palludan, 1984). Hidiroglou and Batra (1995) indicated that the ascorbic acid content of colostrum is more than twice that of subsequently produced milk when measured at seven days of age. In addition, the concentration of ascorbic acid in plasma of piglets at birth (13.1 mg per ml) following uptake of colostrum slowly declined during the first 28 days of age to 3.2 mg per ml. Birke et al. (1993) in a study with a very limited number of sows indicated that restriction of milk intake in piglets by allowing only 12 hours of suckling per day did not influence plasma or tissue ascorbic acid content. The NRC (1998) suggested that the inclusion of vitamin C in swine diets is not required. However, the modern pig may not be able to synthesize adequate amounts of ascorbic acid to meet its need during periods of adverse environmental conditions, disease, or exposure to other stressors (Wariss, 1984). Swine researchers have indicated that under certain situations pigs may need supplemental vitamin C for maximum weight gain and feed use (Mahan et al., 1966; Yen and Pond, 1981; Mahan and Saif, 1983; Mahan et al., 1994; de Rodas et al., 1998). However, there is nearly an equal number of reports that did not show enhanced performance (Brown et al., 1970; Partridge and Brown, 1971; Leibbrandt, 1977; Yen and Pond, 1983, 1984, 1987; NRC, 1998). Reasons for this inconsistency may be that unpredictable environmental and psychological stresses imposed on swine may increase requirements for ascorbic acid. In explaining the lack of vitamin C effect on weight gain in their study, Yen and Pond (1988) suggested that the weight gain of the control pigs was so high that further improvement by dietary manipulation may have been unachievable. The age of pigs studied can influence the response to vitamin C (Mahan et al., 1994). Likewise, Cromwell et al. (1970) reported no benefit in adding vitamin C to the diets of growing pigs.

The level of available dietary energy is a major factor in determining the amount of ascorbic acid available to the pig (Brown et al., 1970; Brown et al., 1975; Brown, 1984). Serum ascorbic acid concentrations as well as urinary output are directly related to the level of energy in the diet. It was also found that a minor stress such as individual penning will evoke a positive growth response from supplementary ascorbic acid, especially in animals fed a “low-energy” diet. Dietary energy is able to cause a shift in ascorbic acid synthesis because of restrictions on amount of free glucose available for this synthesis. Brown and King (1977) suggested that glucose level may control the production of ascorbic acid. Dvorak (1974) also concluded that glucose concentration is an important and positive factor influencing the amount of endogenous synthesis of ascorbic acid.

If a need for dietary vitamin C exists in swine, the newly weaned pig would seem to be the class of swine most likely to be deficient. Sow’s milk contains a high concentration of vitamin C at parturition, but the level drops dramatically toward weaning. For the baby pig, the general consensus is that ascorbic acid blood level increases with colostrum intake, drops at weaning, and slowly increases after seven weeks to the mature level (Wegger and Palludan, 1984).

Handling practices at weaning (especially early weaning), which are generally considered to be stressful, including transport and mixing with unfamiliar pigs, have been shown to deplete ascorbate from the body. Warriss (1979) investigated the concentration of ascorbic acid in adrenal glands of pigs subjected to various pre-slaughter treatments. Warriss (1979) concluded that depletion of ascorbic acid from the adrenal glands could be utilized as a measure of the stress experienced by animals during the pre-slaughter period. Warriss (1981) also investigated the effect of body size on ascorbic acid content and weight of adrenal glands. He concluded that in pigs the concentration of ascorbic acid remained fairly constant as body size increased while the relative adrenal gland weight decreased. However, Kornegayet al. (1986) did not find a significant effect of nursery temperature on the response of weanling pigs to supplemental vitamin C. The humoral immune response and corticoid levels were not influenced by supplemental vitamin D. Yet, in view of decreased plasma vitamin C concentration and dramatic changes in nutritional, social and other environmental factors associated with weaning, it was suggested that the beneficial response from supplemental vitamin C with weanling pigs may be related to suppression of postweaning subclinical disease (Yen and Pond, 1981). In a study with growing pigs between the age of four and seven weeks, Park and Harrison (1990) reported an improvement in nursing pig performance (6% improvement in daily gain; 5% improvement in gain:feed) resulting from vitamin C supplementation in tap drinking water.

Spontaneous scurvy as a result of a genetic defect was observed in a swine production herd among two- to three-week-old piglets (Jensen et al., 1983; Jensen and Basse, 1984). Closer observation revealed that all pigs were from the same boar. Analysis of their blood and tissues revealed only a very small concentration of vitamin C. The 3:1 ratio between normal and affected pigs was characteristic of simple autosomal recessive inheritance in matings between nonaffected carriers. Liver microsomes were shown to be incapable of synthesizing ascorbic acid in vitro even with L-gulonolactone as substrate (Jensen and Basse, 1984). Schwager and Schulze (1997; 1998) utilized vitamin E-deficient pigs as animal models to investigate the effect of ascorbic acid on lymphocytes and leukocytes. They reported that ascorbic acid selectively influences the proliferation of B-lymphocytes and negatively acts on interleukin-2 production by T-lymphocytes when a threshold of saturation is exceeded. Furthermore, it appears that ascorbic acid influences leukocyte function as the production of reactive oxygen intermediates by polymorphonuclear leukocytes decreased in pigs supplemented with ascorbic acid. In agreement with other evidence that vitamin C has a stimulatory effect on the immune responsiveness of swine, Kristensen et al. (1986) indicated that vitamin C-deficient pigs’ lymphocytes had a reduced response to the mitogens concanavalin A and phytohemagglutinin.

Fortification Considerations

Supplementation of vitamin C would not normally be recommended for livestock species under typical management and feeding regimens. As previously mentioned, stress conditions do affect vitamin C synthesis so supplementation considerations must be taken into account. Kolb (1984) summarized various types of stress that apparently have increased demands while reducing the animals’ capability to synthesize vitamin C:

  • (1) Dietary conditions: deficiencies of energy, protein, vitamin E, selenium, iron, etc.
  • (2) Production or performance stress.
  • (3) Transportation, animal handling and new environmental location stress: animals placed in new surroundings (e.g., weaned pigs from different litters placed together) and stressful management practices (e.g., castration, tail docking and ear notching).
  • Piglets are protected from many pathogens by passive transfer of immunoglobulins (Stokes and Bailey, 1998) for the first few weeks of life, but these begin to wane just days after birth. Early stimulation of the immune system may enhance innate immune defenses during this period of immune development that is punctuated with many stressors. Eicher et al. (2006) investigated the efficiency of vitamin C and β-glucan (a yeast product) alone and in combination as a growth or an immune enhancer in young pigs before an endotoxin challenge. The results indicated that vitamin C and β-glucan supplementation had immunomodulating effects in young pigs, with evidence of a synergistic effect of the combination.
  • During transport to an abattoir, pigs are exposed to different stressors (e.g., change of temperature, noises, and movements). The stress caused by this transport may affect animal welfare and increase economic losses related to mortality, carcass damage, and decreased meat quality. Peeters et al. (2005) determined the effects of supplemental vitamin E, vitamin C, magnesium and tryptophan on stress responses (i.e., heart rate variable, behavior, stress hormones and intermediary metabolites) of pigs undergoing a transport simulation. Supplementation with each of these nutrients improved the coping ability of pigs during transport simulation compared with the negative control treatment. Vitamin C supplementation had the least effect, whereas vitamin E acted most effectively. In this study, however, the effect of vitamin C as a vagal stimulator was visible.
  • (4) Disease and parasites: Fever and infection reduce blood ascorbic acid, while parasites may disturb vitamin C synthesis and increase requirements for the vitamin.
  • With regard to dietary conditions, Yen et al. (1985) did not observe a mutual sparing effect on plasma level of vitamin E or vitamin C in weanling pigs whose low vitamin E-selenium diets were supplemented with vitamin E or C. Therefore, these authors concluded that dietary vitamin C supplementation probably would not alter the requirement of vitamin E or selenium in weanling pigs. On the contrary, Lauridsen and Jensen (2005) report beneficial effects of vitamin C supplementation on vitamin E metabolism in postweaning piglets. Vitamin C supplementation after weaning increased liver alpha-tocopherol and serum immunoglobulin M concentration and vitamin C supplementation increased the proportion of the RRR-alpha-tocopherol at the expense of the RRS-stereoisomer form of alpha-tocopherol in alveolar macrophages of the piglets.
  • Hutagalung et al. (1969) reported that including ascorbic acid (1,100 mg per kg diet) (500 mg per lb) in pig diets to which cholesterol and lard had also been added, slightly reduced serum lipid levels, and also reduced cholesterol content of the Longissimus dorsi muscle and and fat. In addition, serum and liver cholesterol levels were decreased significantly compared with those for pigs fed a similar diet without ascorbic acid. A hypocholesteremic effect of ascorbic acid was reported in humans and in laboratory animals by early researchers (Myasnikov, 1964). It has been proposed that ascorbic acid causes a decreased rate of cholesterol synthesis and an increased rate of catabolism, resulting in increased excretion of bile acids from the liver.

The literature concerning efficacy of supplementation of swine diets with ascorbic acid is conflicting. Young pigs and boars seem to be more likely to respond to vitamin C supplementation than other classes of swine. Perhaps the inconsistency of results is due to uncontrolled stress or genetic differences (Brown, 1984) or the form and stability of the ascorbic acid source. Tomes and Wilson (1990) were unable to confirm any production benefits of including extra energy and (or) vitamin C in the diets of sows during late pregnancy. Yen and Pond (1983) concluded that daily supplementation of 1 g of vitamin C to either gilts or sows from day 108 of gestation through day 7 of lactation did not improve reproductive or lactation performance of swine. Lynch and O’Grady (1981) did not find any improvement of postnatal piglet survival when dietary vitamin C was provided to sows during the final week of pregnancy. Although the incidence of stillbirths was reduced, the difference was not statistically significant. In 1984, Carmona Garcia reported that the number of stillborn piglets and the incidence of preweaning mortality were reduced when sows were fed 1 g vitamin C per day from throughout gestation until weaning. Corino and Simondi (1986) indicated that piglet mortality at seven days and 31 days of age for sows fed supplemental ascorbic acid during late gestation and early lactation was numerically lower. Jewell et al. (1981) reported a significant increase in average daily gain in one of two experiments in which dietary vitamin C was provided to neonatal pigs. Leibbrandt (1977) and Siwecki (1985) were unable to detect a significant improvement in performance of neonatal pigs that received dietary ascorbic acid supplementation. Chiang et al. (1985) reported that supplemental vitamin C slightly improved the growth performance of growing-finishing pigs but did not affect weanling pig performance. Although Cromwell et al. (1969) found some evidence that 220 mg of ascorbic acid per kg (100 mg per lb) diet slightly improved gains and resulted in lower feed:gain ratios, the response in performance of growing pigs was not consistent across the three experiments. Cleveland et al. (1983; 1987a, b) investigated whether the addition of vitamin C to growing-finishing boar diets might improve metabolism and lead to better growth, increased feed conversion, or improved feet and leg structure. However, only straightness of front legs was improved by supplemental vitamin C. The lack of consistent results in various studies could probably be due to instability of the vitamin C utilized in the studies (de Rodas et al., 1998). In one study, de Rodas et al. (1998) were able to observe improved performance in young pigs when their diets were supplemented with a stable source of vitamin C, (L-ascorbyl-2-polyphosphate). Mahan et al. (1994) also observed a beneficial effect of ascorbic acid on performance of pigs during the first 14 days after weaning when magnesium-L-ascorbyl-2-phosphate was included in their diet.

Early weaning in pigs has been shown to decrease vitamin C levels in the liver and testes seem to indicate that maximal synthesizing capacity is not developed until about eight weeks of age, thus indicating a possible advantage with supplementing milk replacer products with vitamin C (Wegger and Palludan, 1984). Grummer et al. (1947) reported that feeding 100 mg of crystalline vitamin C to newborn pigs immediately after birth increased the plasma level of vitamin C by more than 2.0 mg. Sandholm et al. (1979) reported that umbilical hemorrhages occurring in piglets immediately after birth can be prevented by supplementing the sows’ feed with 1 g of ascorbic acid per day during the last week of gestation (Illus. 6-2).

Illustration 6-2: Vitamin C Deficiency, Naval Bleeding Syndrome

Umbilical cords of a bleeding piglet (left) andof a normal piglet (right), aged 10 hours. Prevention of naval bleeding has resulted from preparturient administration of ascorbic acid.

Courtesy of Marcus Sandholm, College of Veterinary Medicine, Helsinki, Finland

The intensive selection that has taken place for several decades in the swine industry may have altered the enzymatic constitution of animals so that ability to synthesize vitamin C has changed. Furthermore, modern intensive production systems and continuous demand for higher productivity may have increased the requirement of swine for ascorbic acid. Feeding practices in swine production have also changed, the tendency being to use more processed feedstuffs that, practically speaking, contain no measurable ascorbic acid (North Central Region-89, 1989). Since vitamin C can be synthesized at the tissue level by swine, it has been held by many nutritionists that providing supplemental vitamin C to swine would be senseless. Recent data suggest that supplementation with ascorbic acid should be considered as a management alternative to prevent vitamin C deficiencies when swine are stressed. However, Brown and Partridge (1971) reported data that suggested ascorbic acid offered little benefit in relief of crowding stress. Yet, de Rodas et al. (1998) found evidence that supplementation of weanling pig diets with a stable source of vitamin C improved performance during the high-stress postweaning period. They indicated that this supplementation may be particularly beneficial to pigs weaned at a very early age. Riker et al.(1967) investigated the influence of controlled temperatures on growth rate and plasma ascorbic acid values in growing pigs. Higher temperature was associated with decreased weekly plasma ascorbic acid. When ascorbic acid levels were lowest, weight gains were highest. Recent research has focused on utilizing vitamin C supplementation to improve meat quality in addition to increasing performance of pigs. Mourot et al.(1992) reported that vitamin C supplementation slightly but not significantly increased average daily gain and decreased the feed conversion ratio of pigs between a body weight of 60 and 100 kg (132 and 220 lb). These authors also indicated that at 250 mg ascorbic acid per kg (114 mg per lb) of diet, optimum effects on meat quality characteristics were obtained. The meat color index was improved and muscle pH at 24 hours after slaughter was increased in both the semi-membranous muscle and longissimus dorsi muscle. Rajic et al. (1977) found that vitamin C provided the greatest effect on muscle tissue color when hogs were provided a diet containing 75 mg vitamin C per kg (34 mg per lb). McCampbell et al. (1974) reported that high levels of dietary ascorbic acid (800 mg per kg or 364 mg per lb) of diet lightened the loin color of pigs. Recently, Kremer and Stahly (1999) reported that feeding pigs a diet containing 783 or 2,348 ppm vitamin C for only four hours prior to slaughter increased muscle pH and darkened the color scores of pork. Osborne et al. (1998) indicated that the response to vitamin supplementation on pork quality may be sex related.

Rajic (1971) investigated whether or not ascorbic acid would prevent the development of pale, soft and exudative (PSE) meat in swine. Administration of 75 mg ascorbic acid per kg (34 mg per lb) of feed from the beginning to the end of fattening resulted in the greatest decrease in the percentage of PSE muscles. Cabadaj et al. (1983) investigated the effects of vitamin C in the prevention of PSE and found inconsistent results. Sevkovic et al. (1976) indicated that vitamin C was in certain situations important for reducing PSE and muscle degeneration in pork. Hoppe et al. (1989) provided evidence that the porcine stress syndrome reflects an antioxidant abnormality. Increasing the antioxidant content of the ration by elevating the vitamin E and C supplementation provided protection at the biochemical level to stress-susceptible pigs.

When providing supplemental ascorbic acid, it is advisable to use a stabilized form. Chiang et al. (1985) indicated that uncoated vitamin C kept at room temperature (25°C) was less stable than when stored at lower, outside temperatures (3° to 9°C). Yen and Pond (1988) evaluated whether or not dietary inclusion of rutin, a flavonoid that had been demonstrated in the past to increase the biological value of vitamin C in guinea pigs, would enhance the effect of vitamin C on performance of weanling pigs. They were unable to observe an effect on biologic potency of vitamin C for weanling pigs under the conditions of their experiment. In recent years, the stabilized derivatives of the ascorbic acid molecule have been utilized successfully in experiments evaluating performance of swine.

Vitamin Safety

A number of studies with poultry, swine and laboratory animals have shown no deleterious effect when the animals were fed high levels of vitamin C (NRC, 1998). Research with swine (Brown et al., 1975; Chavez, 1983) has indicated that the dietary vitamin C intakes of as much as 1.0% of the diet did not adversely affect the animals. These studies, however, were less than 60 days in duration.

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