|Nisbet, David - Dave|
Submitted to: Poultry Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/11/2006
Publication Date: 5/20/2007
Citation: Dunkley, K.D., McReynolds, J.L., Hume, M.E., Dunkley, C.S., Callaway, T.R., Kubena, L.F., Nisbet, D.J., Ricke, S.C. 2007. Molting in Salmonella enteritidis-challenged laying hens fed alfalfa crumbles. I. Salmonella enteritidis colonization and virulence gene hilA response. Poultry Science. 86:1633-1639. Interpretive Summary: Salmonella has been shown to cause health problems in humans that eat adulterated poultry products. There is an increased risk of eggs becoming contaminated with Salmonella after molting. In this study, we looked at an alfalfa diet for its effectiveness in reducing Salmonella and virulence gene (hilA) expression during an induced molt. Previous research has shown that this product when given to birds will reduce the overall numbers of Salmonella bacteria in the gastrointestinal tract. We wanted to determine if the virulence factors associated with Salmonella were also affected by alfalfa. When the birds were treated with alfalfa, Salmonella was reduced and the virulence expression was reduced in the bird. This finding is important to the commercial egg laying industry because of new regulations and policy that will limit Salmonella.
Technical Abstract: The objectives of this study were to enumerate Salmonella Enteritidis (SE) in fecal, cecal and internal organs and compare the level of virulence gene (hilA) expression within experimentally challenged laying hens fed different dietary molt induction regimens. Twelve Salmonella-free single comb Leghorn hens (>50 wks old) were randomly assigned to each of six dietary or experimental challenge treatment groups in two trials; (1) feed withdrawal SE+ (FW+), (2) full fed SE+ (FF+), (3) 100% alfalfa crumble SE+ (ALC+), (4) feed withdrawal SE- (FW-), (5) full fed SE-, and (6) 100% alfalfa crumble SE- (ALC-). A forced molt was induced by a 12-day alfalfa diet and a feed withdrawal regimen. On day 4 of the molt, all hens in groups 1, 2 and 3 were challenged by crop gavage with 1-mL of inocula containing approximately 10**6 colony forming units (cfu) of nalidixic acid and novobiocin (NA and NO) resistant SE (phage type 13A). At the conclusion of both trials, all hens were euthanized and SE were enumerated in the cecal contents, liver, spleen, ovaries. In addition, fecal (days 4 and 8) and cecal samples (necropsy at day 12) were collected post challenged from treatment group 1, 2 and 3 (SE+) for quantifying hilA expression by PCR. In both trials all non-challenged birds were SE negative and therefore no further analysis was done. The results in both trials for SE positive birds indicate that the ALC+ diets effectively reduced the number of SE in the cecal content when compared to the FW+ hens. In trial 1, a 2-fold reduction in SE colonization was observed in the ALC+ hens (log10 SE of 1.99) compared to the FW+ hens (log10 SE of 3.89). In Trial 2, a 4-fold reduction in SE colonization was observed in the ALC+ hens (log10 SE of 1.27) compared to the FW+ hens (log10 SE of 5.12). In both studies Salmonella colonization in liver, spleen and ovaries were significantly (P less than or equal to 0.05) higher in FW+ hens compared to ALC+ and FF+ treatments groups. Relative expression of hilA in all treatment groups was significantly (P < 0.05) higher in FW+ compared to FF+ and ALC+ groups. Full-Fed+ and ALC+ groups showed no significant difference (P < 0.05) in hilA expression. In Trial 2, hilA expression in FW+ hens was 3.2-, 4.2-, and 1.9-fold higher for Days 6, 11 and 12 respectively, when compared with to ALC+ hens. The results of these studies support the concept that changes in the gastrointestinal (GI) tract microenvironment such as those created during feed deprivation, encourage SE virulence and susceptibility in molted hens. Furthermore, GI tracts of hens fed alfalfa crumble during forced-molt may be more inhibitory to SE virulence expression and subsequently these hens are more resistant to SE colonization and infection.