Experimental models of porcine post-weaning colibacillosis and their relationship to post-weaning diarrhoea and digestive disorders as encountered inthe field

The aim of this study was to develop a reliable model system of porcine pos t-weaning colibacillosis, and in doing so to assess the primary relationshi p of enterotoxigenic Escherichia coli to post-weaning diarrhoea and digesti ve disorders as encountered in the field. Six sequential experiments were c arried out using 168 SPF piglets weaned into an optimal controlled environm ent at 28 days of age. The piglets were allocated to 23 treatment groups, 1 7 of which were inoculated either orally or intragastrically with enterotox igenic strains of E. coli (LT+, STI+, STII+) possessing adhesive factors in cluding K88 (F4). The piglets were challenged either once (Day 4 post-weani ng) or on several days post-weaning, with the challenge load for each inocu lation varying from 10(8) to 10(12) CFU. Overall 14.5% of inoculated pigs developed severe illness and died: these h ad lesions in their digestive tracts typical of colibacillosis, Diarrhoea o ccurred on at least 1 day in 50% of inoculated pigs, but was transient (1.7 days on average), appeared very soon after challenge (sometimes within hal f a day), and was accompanied by signs of depression and low weight gain. G enerally a prompt recovery then occurred. In the second 2 weeks post-inocul ation daily weight gain reached the same level in most inoculated groups of pigs as in the uninoculated controls. Only a small number of pigs develope d a chronic enteritis lasting several days, as is typically observed in fie ld cases. Diarrhoea was more common in the piglets that were tested adhesiv e positive to the K88 fimbriae receptor, but the disorders were no more sev ere in these animals. The response of all pigs depended primarily on the in oculum used, and especially on the challenge load. Although enterotoxigenic E. coli are clearly important in the aetiology of post-weaning diarrhoea, other factors are also required for the production of the: chronic post-wea ning digestive disorders and ill-thrift that are commonly encountered in co mmercial piggeries. (C) 2000 Elsevier Science B.V. All rights reserved.