Effects of dietary combinations of organic acids and medium chain fatty acids as a replacement of zinc oxide on growth, digestibility and immunity of weaned pigs

• Dietary organic acids (OA) mix increased feed intake and growth of weaned pigs.
• Dietary OA mix improved AA digestibility and expression of AA transporters.
• Dietary OA mix promoted intestinal Lactobacillus proliferation.
• Dietary OA mix stimulated jejunal regulatory cytokine (TGF-β) expression.
• Dietary OA mix downregulated jejunal proinflammatory cytokine expression.

Two experiments were conducted to evaluate effects of dietary solid mixture of organic acids and medium chain fatty acids (MCFA) as a replacement of zinc oxide (ZnO) on growth, digestibility and immunity of weanling pigs. In Exp. 1, the diet with supplemental antibiotics (containing pure Colistin sulfate and Enramycin, respectively, at 0.02 g/kg diet) and ZnO (2.5 g/kg diet) was used as the control (CON) group, and another diet without supplemental ZnO was prepared by inclusion of the SF3 (containing calcium formate, calcium lactate, citric acid and MCFA at 340, 160, 70 and 130 g/kg, respectively) at 3 g/kg diet. A total of 120 crossbred piglets (21-day old, 6.36 ± 0.80 kg) were fed the same commercial prestart diet for one week and then fed the CON or SF3 diet for four weeks (ZnO was no longer supplemented in the CON diet during the second two-weeks), with 6 replicate pens (10 piglets/pen) per diet. Compared with the CON-fed piglets, the SF3-fed piglets had higher (P < 0.001) feed intake during the first two experimental weeks, higher (P < 0.05) body weight at the end of each of the four experimental weeks, and lower (P < 0.01) ratio of feed to gain during the first experimental week. In Exp. 2, diets were the same as in Exp. 1, except that chromium oxide was included at 3 g/kg diet at the expense of corn to evaluate apparent ileal digestibility (AID) of dietary amino acids (AA). Fourteen crossbred piglets (28-day old, 9.05 ± 1.38 kg) were housed individually in metabolism cages, fed the CON diet for one week and then fed the CON or SF3 diet for two weeks with 7 pigs (4 female and 3 male) per diet. Compared with the CON-fed piglets, the SF3-fed piglets had higher (P < 0.05) AID of a majority of AA, lower (P < 0.05) plasma tumor necrosis factor alpha (TNF-α) but higher (P < 0.05) plasma immunoglobulin-G concentrations, more (P < 0.05) ileal and rectal Lactobacillus content, and upregulated (P < 0.05) jejunal AA transporters (EAAT3 and CAT2) and regulatory cytokine (transforming growth factor beta) expression but downregulated (P < 0.05) jejunal proinflammatory cytokine (TNF-α) expression. Taken together, dietary supplementation with a mixture of organic acids and MCFA contributed more than ZnO to growth of weanling pigs under commercial conditions. The improved growth of pigs was associated with increased AA digestibility and immunity. The stimulated regulatory cytokine expression and downregulated proinflammatory cytokine expression might be associated with increased proliferation of Lactobacillus following organic acids consumption.