Folic acid needs for livestock may be supplied by complex practical diets (Maynard et al., 1979). Also, for most species, substantial quantities of folic acid are provided through microbial synthesis. Nevertheless, field observations have been made of diets that provide insufficient folic acid. Green forage is an excellent source of folic acid. Supplementation of folic acid would be most needed when animals are in confinement without access to fresh or preserved green forages. The successful treatment of field cases of folic acid deficiency and improved reproductive performance observed with supplemental folic acid have demonstrated that commercial feeds not supplemented with folic acid do not always supply adequate quantities of the vitamin to swine.
Folic acid supplementation is also of importance when swine receive diets that contain folic acid antagonists such as sulfa drugs and grains contaminated with toxin-producing molds. Depending on a given year and climatic and harvesting conditions, a large percentage of the United States corn crop may contain some mold contamination. Therefore, folic acid supplementation should have a positive effect in many commercial swine operations. This would likely be an even more important consideration in developing tropical countries or regions where climates favoring mold growth are optimized. Individual responses to folic acid supplementation to counteract mold effect will obviously vary with the class of livestock being fed, species of mold present and the levels of toxin encountered (Bhavanishkankar et al., 1986).
Although the research with reproducing female swine is limited, a pattern due to folic acid supplementation is evident. There is a consistent increase in total and live pigs born when reproducing females receive supplemental folic acid during gestation (Ensminger et al., 1951; Easter et al., 1983; Matte et al., 1984a, b; Tremblay et al., 1986; Lindemann and Kornegay, 1989; Tremblay et al., 1989; Matte et al., 1990a). The increase has occurred at dietary supplementation levels from 0.2 mg per kg (0.09 mg per lb) (Easter et al., 1983) to 15 mg per kg (6.9 mg per lb) (Matte et al., 1990b) as well as with folate injections throughout the first 12 weeks of gestation (Matte et al., 1984b). It seems apparent and logical that supplementation must occur in early gestation; late gestational or lactational supplementation has been without effect on reproductive performance (Pharazyn and Aherne, 1987). However, Matte et al. (1992) indicated that supplementation of 15 mg folic acid per kg of diet during both gestation and lactation maximized growth of piglets in their study. The response to folic acid appears to be greater in conditions of increased ovulation (e.g., sows versus gilts, flushed versus non-flushed), which suggests that there may be breed differences in response to folic acid supplementation (Lindemann, 1988).
Gadient (1986) considered folic acid to be very sensitive to heat and light, slightly sensitive to moisture and insensitive to oxygen. Folic acid can be lost during storage of premixes, particularly at elevated temperatures (Frye, 1978). After three months of room temperature storage, 43% of the original folic acid activity was lost. Verbeeck (1975) found folic acid to be stable in premixes without trace minerals but that there may be as much as 50% loss in a premix with trace minerals kept at room temperature for three months. Adams (1982) reported only 38% retention of folic acid activity in a premix without trace minerals after three weeks at 45°C. However, he reported 57% retention of activity after three months at room temperature.
