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Swine: Vitamin C
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 that 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:

  • Dietary conditions: deficiencies of energy, protein, vitamin E, selenium, iron, etc.
  • Production or performance stress.
  • 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).
  • 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.

Hutagalung et al. (1969) reported that including ascorbic acid (1,100 mg per kg diet) in pig diets to which cholesterol and lard had also been added, slightly reduced serum lipid levels, and also reduced cholesterol content of the L. dorsi 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 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 vitamin C addition to growing-finishing boar diets might improve metabolism and lead to better growth, increase feed conversion, or improve their 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 a recent 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 liver and tests 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. 1).

 
Illustration 1

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. These authors also indicated that at 250 mg ascorbic acid per kg of diet, optimum effects on meat quality characteristics were obtained. The meat color index was improved and 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. McCampbell et al. (1974) reported that high levels of dietary ascorbic acid (800 mg per kg 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 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 defect 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. In feed storage experiments, coated ascorbic acid was found to be four times more stable than crystalline vitamin C (Kolb, 1984). Adams (1978) reported that coated (ethylcellulose) ascorbic acid showed a higher retention after processing than the crystalline form, 84% versus 48%, respectively. Retention of vitamin C in mash feed was fairly good but with extended storage time and elevated 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 the crystalline 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. One such molecule, magnesium-L-ascorbyl-2-phosphate, was found to be effective in improving the performance of pigs during the first 14 days after weaning (Mahan et al., 1994). This modified form of vitamin C protects the molecule acid by chelating a magnesium and phosphate ion to the ascorbic acid. Another stable form of vitamin C, L-ascorbyl-2-polyphosphate, has been utilized successfully to document the beneficial effects of dietary vitamin C on weanling pig performance (de Rodas et al., 1998).

 
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