The influence of fat protection of calcium formate on growth and intestinal defence in Escherichia coli K88-challenged weanling pigs

An experiment was conducted to test whether free or fat-protected dietary calcium formate improves the growth and health of weanling pigs that may or may not be susceptible to intestinal adhesion of enterotoxigenic Escherichia coli (ETEC), when orally challenged with ETEC. Sixty pigs, weaned at 21 days of age (day 0), were divided into three groups (20 pigs each), balanced for number, litter and live weight, and fed the same base diet but three different 30.5 g/kg supplementations: a control (CO---with dicalcium phosphate, calcium sulphate, lard and sepiolite); a free calcium formate (FF), with this additive, monosodium phosphate and lard; a fat-protected calcium formate (PF), with this additive and monosodium phosphate only. The final diets did not differ for total calcium and phosphorus content. The pigs, dividually penned, were orally challenged with 1.5 ml of a 10¹⁰ CFU E. coli K88 suspension on day 2 and slughtered on day 7 or 8. Data were analysed using analysis of variance with a three-factor design, including diet, block, sensitivity of intestinal villus to ETEC adhesion, and first level interactions. The factor diet never interacted with the others. Compared to the control diet, the formate supplementations improved growth (P<0.05), feed intake (P=0.062) and G:F (gain:feed) ratio (P=0.063). Both forms of formate addition reduced the faecal score (P=0.062), days of diarrhoea (P<0.05) and total E. coli faecal excretion (P<0.05) but not E. coli K88 faecal excretion, and increased villus height in the small intestine (P<0.05). The number of enterocytes and goblet cells in the ileum was not changed by formate supplementations. In saliva, total IgA activity tended to be reduced by acidifiers (P=0.067). The anti-K88 IgA in the saliva, the blood and the jejunum secretion, and the expression of the TNFα gene in the stomach and jejunum wall were not affected by the diet. The pH of the stomach, the duodenum and the ileum was not affected while the formate reduced the pH in the colon and the caecum. Fat-protected calcium formate did not improve the results obtained with free formate supplementation. Calcium formate has a growth-promoting effect in weanling pigs challenged with E. coli K88, independently of their susceptibility to the intestinal adhesion of this strain. Its action seems to be more related to a general control of the total E. coli rather than of E. coli K88. At the same dietary concentration, no particular advantage comes from using the protected formate instead of the free additive.