Influence of continuous challenge via the feed on competitive exclusion of salmonellas from broiler chicks.
In three replicate trials, chicks were treated orally with a culture of caecal contents from an adult hen and then exposed to continuous challenge from a strain of Salmonella kedougou incorporated in feed at a level of ca 10(2)/g. The contaminated feed was introduced at intervals from 0 to 48 h after treatment. Under these conditions, only one of 119 chicks in 12 separate groups was salmonella-positive at 7 d, compared with 36 of 119 controls, but thereafter protection was less consistent and in some cases the subsequent incidence of infected birds increased during the 3-week rearing period. At 21 d, 14 of 60 treated chicks were positive and 32 of 59 controls. Protection was more evident in chicks challenged 24 or 48 h after treatment than in those groups which received the salmonella-contaminated feed at 0 or 5 h and even untreated, control chicks showed greater resistance to salmonella infection from 24 h onwards. In some control and treated groups containing salmonella-positive birds, contamination of the litter reached ca 10(6) salmonellas/g, thus providing a considerable secondary challenge. Introduction of salmonellas via contaminated feed probably reduces the efficacy of protective treatment under field conditions and helps to explain the more limited success in commercial use.
Impey
C S
CS
Agricultural and Food Research Council, Institute of Food Research-Bristol Laboratory, Langford, UK.
Mead
G C
GC
Hinton
M
M
D000821:Animal Feed; D000818:Animals; D000898:Antibiosis; D002432:Cecum / Q000382:microbiology*; D002645:Chickens; D011201:Poultry Diseases / Q000382:microbiology / Q000517:prevention & control*; D012475:Salmonella / Q000254:growth & development; D012481:Salmonella Infections, Animal / Q000382:microbiology / Q000517:prevention & control*