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High dietary additions of Zn (over EU allowance) required in order to reducing total E.coli and E.coli K88 faecal excretion and IgA production

Research shows that dietary zinc oxide (ZnO) at pharmacological level improves growth and/or reduces diarrhoea in weaned pigs. However, the theories to explain ZnO action conflict with experimental data, and it is not clear if other zinc sources supplied over requirements can improve growth or health of piglet. Thus, dietary strategies to supplement zinc within the EU rules are difficulty identified. Recent findings show also that dietary glutamate reduces villus atrophy after weaning and is an important fuel for the enterocyte. We hypothesized that zinc chelated with glutamate could have a different absorption or channelling into a metabolic pool, compared to the oxide. Our goal was to study the effects of two doses of ZnO or zinc glutamate on growth performance, gut characteristics, health and immunity of weaned pigs.

On day 0, 60 weaned pigs (21 d age), based on live weight and litter, were assigned to 5 dietary treatments: control (C); zinc oxide or zinc-glutamate chelate (Zn-Glu), at 200 or 2500 mg Zn/kg. On d 1, the subjects were orally challenged with 1.5 ml of a 1010 CFU/ml E. coli K88 suspension.

Zinc did not improve growth performance and feed intake, whatever were the source and the level of addition. In experiments with weaning pigs in which growth was positively related to high doses of zinc oxide, the period of observation was longer. Seven days could not have been sufficient to evaluate the influence of zinc supplementation.

On d 4, both high zinc supplementations reduced the total E. coli bacteria and E. coli K88 faecal excretion (P<0.05). Whatever was the source, with Zn supplementations, a trend of reduction of K88-specific IgA was observed in serum on d 4 (P=0.10), but not on d 6, and in saliva on d 6 (P=0.07), but not on d 5. The contemporary reductions of faecal excretion and IgA production suggest that zinc has a local action, and that, likely, the reduced antigenic charge decreases the recruitment of the immune response.

Differences were not detected for specific IgA content in the jejunum secrete. At the sacrifice, when the secrete was sampled, the immune stimulation from E. coli K88 could have been already declining. Effects of the diet were observed on small intestinal morphology, but not equal along different tracts. In the duodenal tract, the villus height was improved by zinc supplementations (P<0.01), whereas crypt depth was not affected. This confirms that zinc can have an important role in the protection of small intestinal structure.

However, in the jejunum and ileum, the morphology was not associated with the increasing zinc additions. For both zinc sources, with high doses of zinc the concentration of this mineral in liver was the triple of the values observed for the control and for the low Zn doses. These results agree with other researches, and suggest that zinc availability was not affected by chelation with glutamate.

High level of zinc from zinc oxide and zinc-glutamate chelate added to weaning pig diet for short term may have an important role in resistance to infection reducing the coliforms multiplication and E. coli K88 gut colonization.

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