Effects of zinc oxide on postweaning diarrhea control in pigs experimentally infected with E-coli

Three experiments were conducted in order to determine the efficiency of four commercial brands of zinc oxide (ZnO) available in Brazil for diarrhea control in weaned pigs and to determine the involved mechanisms. The first experiment was carried out with 36 weaned pigs, divided in six similar groups which were fed ad libitum. Four groups were supplemented with 2400ppm of Zn, but using four different commercial brands, and challenged, three days after the beginning of supplementation with an enteropathogenic Escherichia coli strain (groups 2 to 5). One group (1) did not receive ZnO supplementation, but was inoculated with the same E. coli strain. Another group (6) was neither supplemented with ZnO nor inoculated with E. coli. In the second experiment two groups of weaned piglets were submitted to the same treatments used with the groups 1 and 6 in the first experiment in order to determine the intensity of fecal E. coli elimination. In addition, it was determined in vitro the minimal inhibitory concentration (MIC) of the four commercial brands of ZnO to E, coli strain (experiment 3). The results showed that ZnO supplementation (2400ppm of Zn) Mns efficient in the control off. coli diarrhea, independently of the commercial brands used Pigs that diet nor receive ZnO supplementation had severe diarrhea while those that were supplemented did not show it. Fecal elimination of E. coli was constant from second day after inoculation in all inoculated piglets, suggesting that ZnO did not impair E. coli multiplication in the gut. The amount of Zn in feces and liver was respectively, 21 and 1.5 times higher in supplemented piglets than in the controls. The MIC of Zn was of 256mg/ml, regardless the commercial brands. The constant excretion of E. coli associated with high concentration of Zn in the feces and low diarrhea occurrence suggests, however, that other mechanism than impairment off. coli growth in the gut may exist.