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 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, owing to 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 (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. Recently, 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 the sow and mare that 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 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.
Ascorbic acid content of the sow 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. Additionally, these authors reported that average conception rate in sows increased when boars were supplemented with either 1 or 2 g daily of ascorbic acid compared to controls (Fig. 1). 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.