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Formic acid (actually calcium formate) as a growth promoter for the young pig

The practice of adding organic acid to diets for weaning pigs is quite established. An improvement of growth after weaning has been averagely demonstrated during feeding trials. However data showing that organic acids can positively counteract the presence of post-weaning diarrhoea and of enterotoxigenic E.coli k88 (ETEC) are conflicting. It cannot be excluded that differences in the response to organic acids depend on individual susceptibility to ETEC.

Furthermore gastric acidification reduces gastric release and consequently hydrochloric acid secretion, but its long term effects are not enough studied. 60 pigs, weaned at 21 days, were divided into three groups, balanced for number, litter and live weight and fed: standard balanced diet (C), C + 1.2% of free calcium formate (F), C + 1.2% of fat-protected calcium formate (P). In F and P diets, monosodium phosphate and calcium formate were partial substituted for dicalcium phosphate and calcium sulphate of diet C. Pigs were orally challenged with 1.5 ml of a 1010 CFU Escherichia coli K88 O148 (F4) suspension on day 2, and sacrificed on day 7 or 8.

The supplementation with free calcium formate improved growth (P<0.01) and feed intake (P<0.05) (Fig.1), while only a trend of increase of growth was observed for fat-protected formate (P<0.10). Both forms of formate addition reduced diarrhoea score, days in diarrhoea, total E. coli faecal excretion (P<0.05), and increased the average of villous heights in duodenum, jejunum and ileum (P<0.05). IgA anti E.coli K88 were reduced by formate treatments (P<0.05), in saliva but not in blood and in jejunum secretion (Data not in figure). In saliva, the total IgA activity tended to be reduced by acidifiers (P=0.07). The expression of TNFalfa gene in stomach and jejunum wall was not affected by the diet. The pH of stomach was not affected, while free formate reduced average pH in ileum, colon and cecum, compared to the other dietary treatments.

Pigs fed 12 g/kg calcium formate for 7 or 8 days had a relevant reduction of parietal cells (acid secreting in the stomach), and of expression of H+/K+-ATPase gene (functional to acid secretion) compared to control ones (P<05). This reduction was not observed with fat-protected formate supplementation (same dose).

It is confirmed that formic acid (actually calcium formate) has a growth promoting action for the young pig. This action is explained by a reduction of total E.coli persistence. Our data concerning the use of fat-protected formate are not conclusive. Some positive effect was seen on health, but not on growth. The degree of protection was not tested, but data could lead to suspect that the protection was not homogeneous; the reduction of IgA in saliva observed also with the addition of fat-protected formate could be explained by the presence of some free formate in the product too. The use of this fat-protection is justified only to overcome the negative effect of free formate on gastric morphology.

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