Multisite Controlled Blinded Field Studies to Evaluate the Effect of an Oral Live Escherichia Coli Bivalent F4/F18 Vaccine in Pig Nurseries with Mild Cases of Post-Weaning Diarrhea or Subclinical ETEC Infections.

Abstract Background: Post-weaning diarrhea (PWD) caused by Escherichia coli is a worldwide economically important disease in pigs, linked with increased mortality and weight loss. F4- and F18-enterotoxigenic E. coli (ETEC) are the most diagnosed causes of PWD. The efficacy of live oral E. coli vaccines has been previously demonstrated on farms with confirmed clinical cases of PWD. However, the impact of vaccination in subclinical cases with mild or not noticeable clinical manifestations needed to be assessed. This study evaluated the effect of an oral dose of a live E. coli bivalent F4/F18 vaccine in nurseries without ongoing clinical PWD outbreaks but with a history of pathogenic E. coli circulating within the herd. Two controlled blinded studies were performed under commercial conditions in a total of 6 European sites. Overall, 1941 vaccinated piglets and 1976 control piglets were enrolled and were monitored for health, growth, and feed conversion rate. Results: No clinical outbreak of ETEC PWD has been observed in the tested farms. Two farms faced episodes of non-ETEC enteric diseases that required treatments. Nursery weight gain was not statistically different between groups in these two farms. However, the nursery weight gain of the vaccinated pigs was significantly higher by 0.80, 0.87 and 1.24 kg than of the control pigs in three of the four farms without non-ETEC enteric diseases (p<0.05) and by 0.69 kg (p=0.051) in the fourth one, leading to numerically heavier pigs at the exit of the four nurseries. No statistically difference was observed for the feed conversion rate, though it was numerically lower for vaccinated pigs of the two tested farms. Conclusions: Recent European legislations aimed at reducing the use of antibiotics and banning therapeutic use of zinc oxide in feed are leading to a search for alternatives to compensate animal health impacts and economic losses due to PWD. These studies demonstrate that, even in the absence of convincing clinical signs of PWD, ETEC infections limit nursery pig optimal growth performance that can be mitigated by vaccination with an oral live E. coli bivalent F4/F18 vaccine. These findings corroborate previous studies showing the effect of vaccination in clinical outbreaks of PWD.