Abstract Recent research reported an increase in growth performance when feeding supra-nutritional (up to 18 mg/kg) levels of folic acid to weanling pigs. Therefore, two experiments were conducted to validate these responses in typical U.S. nursery pig diets. In Exp. 1, 360 barrows (5.5 ± 0.03 kg) were used in a 38-d study to evaluate the effects of added folic acid (Rovimix Folic Acid, dsm-firmenich, Plainsboro, NJ) with or without pharmacological levels of Zn on growth performance and fecal dry matter (DM). Treatments were arranged in a 3 × 2 factorial with main effects of folic acid (0, 20, or 40 mg/kg) and Zn (3,000 mg/kg of Zn in phase 1 and 2,000 mg/kg in phase 2 or no Zn other than 110 mg/kg from the trace mineral premix). Diets were corn-soybean meal-based and fed in 2 phases (phase 1 from d 0 to 9 and phase 2 from d 9 to 24). Overall (d 0 to 38), increasing folic acid decreased (quadratic, P ≤ 0.003), average daily gain (ADG), and average daily feed intake (ADFI) with pigs fed 20 mg/kg having the lowest performance. From d 0 to 24, pigs fed diets with pharmacological levels of Zn had increased (P ≤ 0.030) ADG, and ADFI compared to pigs fed 110 mg/kg added Zn; however, no differences were observed in overall performance. Fecal DM was greater (P = 0.007) on d 24 compared to d 9. A trend was observed where pigs fed diets with added Zn had increased (P = 0.080) fecal DM averaged across d 9 and 24. Fecal total short chain fatty acid concentrations were greater (P = 0.053) on d 24 compared to d 9. Isobutyrate increased (linear, P = 0.030) as folic acid increased; however, most samples had nondetectable levels. In Exp. 2, 350 barrows (initially 6.0 ± 0.06 kg) were fed corn-soybean meal-based diets, fed in 3 phases (phase 1 from d 0 to 10, phase 2 from d 10 to 23 and phase 3 from d 23 to 38), and consisted of increasing folic acid: 0, 5, 10, 20, or 40 mg/kg. Overall, ADG, ADFI, and G:F were reduced (quadratic, P ≤ 0.049) as folic acid increased with the poorest performance observed when pigs were fed 20 mg/kg of folic acid. On d 10 and 23, blood samples were collected from 70 pigs to determine serum homocysteine concentration Homocysteine concentrations increased (linear, P = 0.037) with increasing folic acid on d 10; however, no differences were observed on d 23 (folic acid × d interaction, P = 0.069). In conclusion, added folic acid reduced growth performance with pigs fed 20 mg/kg having the poorest performance, and increased serum homocysteine concentrations.
Becker et al. (Sat,) studied this question.