Effects of Dietary Folic Acid Supplementation on Growth Performance and Immune Parameters in Weanling Piglets

In order to study the effects of dietary folic acid (FA) supplementation on growth performance and immune status in weanling piglets, a single factorial randomized block design trial was conducted with six diets supplemented with FA at 0, 0.30, 3.00, 6.00, 9.00 or 15.00 mg/kg. A total of 108 crossbred (Landrace x Yorkshire) castrated weanling piglets (at 21 d of age) were allocated by body weight into 36 feeding cages (3 piglets/cage), which were allotted randomly into six dietary groups (six cages/group). Piglets were fed ad libitum for 24 days. Blood samples were collected on the 24th day. The growth performance and immune parameters were measured. Results showed that FA supplementation increased the serum FA level of weaned piglets (p < 0.01) and tended to increase the body weight (BW) at 45 d of age (p < 0.1) and the average daily gain (ADG) from 29 d to 45 d of age (p < 0.1). FA addition improved the feed efficiency (G/F) from 21 to 45 d of age (p < 0.01) with supplementary FA levels of 0.3, 3.0, and 9.0 mg/kg compared with the control group with no FA supplementation. FA supplementation showed a trend (p < 0.1) to increase the peripheral blood CD3(+)CD8(+) lymphocyte subpopulation and a tendency (p < 0.1) to decrease the CD3(+)CD4(+)/CD3(+)CD8(+) ratio; in particular FA supplementation of 0.3 and 3.0 mg/kg showed significant differences in comparison to the non-supplemented control group. Moreover, FA addition increased the serum interferon-gamma (IFN-gamma) level (p < 0.05) and tended to reduce the ratio of tumor necrosis factor-alpha to interleukin-4 (TNF-alpha/IL-4, p < 0.1) and immunoglobulin G (IgG, p < 0.1) in serum, but had no significant effect on serum IL-4, TNF-alpha, and nitric oxide. In conclusion, FA supplementation up to 3 mg/kg to the diet showed a tendency to improve immune function, while FA supplementation of up to 9 mg/kg improved feed efficiency, which resulted in a trend for higher growth in weaned piglets between 7 to 11 kg BW.