The effect of in ovo or day-of-hatch subcutaneous antibiotic administration on competitive exclusion culture (PREEMPT) establishment in neonatal chickens.

The effect of in ovo or day-of-hatch subcutaneous antibiotic administration on the detection of antibiotic residues in yolk sac or blood serum samples and the potential for observed residues to interfere with competitive exclusion (CE) culture establishment was compared in three experiments. The in ovo or subcutaneous administration of gentamicin sulfate or ceftiofur sodium was associated with detectable levels of antibiotic residues in yolk sac or blood serum samples in Experiment 1. Further, the ability to detect antibiotic residues in day-of-hatch chicks was associated with reduced levels of CE culture establishment when cecal propionate level, an indicator of PREEMPT establishment, was determined following PREEMPT application by oral gavage on the day of hatch in Experiments 1 and 2. Restricting chicks from feed, as opposed to providing access ad libitum to a starter ration, for 6 h immediately following administration of PREEMPT improved (P < 0.05) CE culture establishment in Experiment 2 in nonantibiotic injected control chicks, but did not affect (P > 0.05) experimental groups receiving either gentamicin sulfate or ceftiofur sodium by either in ovo or subcutaneous routes. The in ovo administration of 0.1 or 0.2 mg ceftiofur sodium to individual embryos on Day 18 of embryogenesis in Experiment 3 was associated with marked depressions (P < 0.05) in cecal propionate levels compared with uninjected control chicks. When feed was restricted and the time of PREEMPT administration was delayed for 48 or 72 h posthatch, mean cecal propionate levels in in ovo ceftiofur sodium-injected chicks were not significantly different (P > 0.05) from controls, indicating a time- and feed restriction-associated effect on improving CE culture establishment.

Assessment of the long-term shedding pattern of Salmonella serovar choleraesuis following experimental infection of neonatal piglets.

In the United States, swine salmonellosis is most often attributed to infections by Salmonella serovar choleraesuis. As a host-adapted pathogen rarely found in nonswine sources, S. choleraesuis is thought to be spread primarily via horizontal transmission, with carrier animals playing an important role. Little has been reported regarding infection of neonatal piglets, particularly regarding their potential to become carriers. Evidence reported herein demonstrates that piglets experimentally infected by S. choleraesuis at 2 days of age were capable of shedding the pathogen for up to 85 days postinfection, at which time the study was concluded. This study also presents findings supporting the use of GN-Hajna as a preenrichment medium for the isolation of S. choleraesuis.

Effects of chicken-derived cecal microorganisms maintained in continuous culture on cecal colonization by Salmonella typhimurium in turkey poults.

A characterized, chicken-derived, competitive exclusion culture of cecal bacteria was evaluated for effectiveness in the reduction of Salmonella typhimurium cecal colonization in growing turkey poults. The culture was administered by crop gavage on the day of hatch. All groups were challenged orally on Day 3 with 10(4) S. typhimurium. Compared with untreated controls, the percentage of poults that were Salmonella cecal-culture-positive at 10 d of age was significantly reduced (P < 0.05) in the poults provided culture. Additionally, the culture-treated poults had significantly (P < 0.05) fewer Salmonella per gram of cecal contents than the controls. The results indicated that treatment of turkey poults with the characterized chicken-derived culture effectively decreased Salmonella cecal colonization.

Evaluation of Salmonella serotype distributions from commercial broiler hatcheries and grower houses.

By conventional trayliner (hatcheries) and drag swab assembly (broiler houses) culture methods, the isolation distribution of Salmonella serotypes from five commercial broiler hatcheries (three sample times) and 13 broiler farms (eight sample times) was evaluated. A total of 11 different Salmonella serotypes were isolated from hatcheries, with Salmonella heidelberg (9/30) and Salmonella kentucky (6/30) accounting for 50% of the total isolations. Of 700 chick paperpad trayliners sampled, regardless of lot (breeder flock source) or hatchery, 12% were positive for Salmonella. When 10 individual trayliners were cultured from individual lots (same breeder flock source), Salmonella was detected in 24/57 lots (42%). Multiple serotypes were simultaneously isolated from the same lot on three occasions (6%). Of the 21 lots that were serially sampled, the Salmonella serotype detected was different within lots eight times (38%) on at least one occasion of two or more sampling times. Of the 196 individual broiler houses sampled, 44 were positive for Salmonella (42%). Twelve different serotypes were isolated from broiler houses during this study. The serotypes isolated most frequently were S. heidelberg (34/94) and S. kentucky (22/94). These two serotypes accounted for 59.6% (56/94) of the total broiler house isolations. Of the 38 houses that were serially sampled, two or more serotypes were detected in the same broiler house on 20 occasions (53%). Of the 38 serially sampled houses (four or more times), a consistent Salmonella serotype was detected in five houses (13%). In only 5 of the 38 (13%) serially sampled houses did we fail to detect Salmonella on four or more samplings. No significant difference in Salmonella isolation frequency was observed between poultry houses using new or used litter. These data support previous findings indicating that paratyphoid Salmonella serotypes are prevalent in some broiler hatcheries and houses. Further, the observation of multiple serotypes simultaneously and serially isolated from the same breeder hatchery lots suggests that breeder flocks may be infected with more than one serotype, possibly providing a source for multiple serotype infections in progeny grower flocks.

Enhancement of phagocytosis and bacterial killing by heterophils from neonatal chicks after administration of Salmonella enteritidis-immune lymphokines.

During the first week post-hatch, chickens demonstrate an increased susceptibility to infection by bacteria such as Salmonella. The purpose of the present study was to evaluate the effects of immune lymphokines on phagocytosis and killing activities of heterophils in chicks during the first 1-7 days of life. Lymphokines isolated from chicken splenic T-cells harvested from Salmonella enteriditis (SE)-hyperimmunized hens (SE-ILK), have in past experiments, demonstrated augmentation of heterophil activity in day-of-hatch chicks resulting in protection from SE organ invasion. The present experiments reveal significant increases (p<0.05) in heterophil phagocytosis and killing when comparing chicks treated with SE-ILK to control groups in vitro. In SE-ILK-treated groups, a two-fold or greater increase is noted in heterophil phagocytosis within I h of incubation as compared to controls. Heterophils isolated from 1-day-old and 4-day-old chicks treated with SE-ILK killed significantly greater numbers (p<0.05) of SE than heterophils isolated from control groups. By Day 7 post-hatch, significance is not noted in the killing activity of heterophils from treated groups when compared to control groups. However, heterophils from SE-ILK groups continue to kill greater numbers of SE than control groups. These data support SE-ILK augmentation results in an enhanced heterophil function in chicks during the greatest period of susceptibility to Salmonella invasion.

Experimental and natural infection of early weaned pigs with Salmonella choleraesuis.

A model for experimental and natural infection of early weaned pigs with Salmonella choleraesuis, the aetiologic agent of swine paratyphoid, has been developed. An oral dose of 10(8) colony forming units (cfu) of S choleraesuis caused 100 per cent infection of 10 pigs inoculated, as indicated by recovery of the challenge organism from ileocolic lymph nodes collected at necropsy seven days post challenge. Seven of the pigs were observed shedding S choleraesuis at least once post S choleraesuis challenge. The cumulative incidence of shedding was 30 per cent and was sufficient to infect four of 10 pigs exposed naturally. Oral challenges with less than 10(8) cfu S choleraesuis were less effective in infecting early weaned pigs and did not result in natural transmission.

Early Salmonella challenge time and reduction in chick cecal colonization following treatment with a characterized competitive exclusion culture.

Broiler chicks were treated by oral gavage on the day of hatch with a continuous-flow competitive exclusion culture (PREEMPT). At 4 h, 1 day, or 2 days posttreatment, chicks were challenged by oral gavage with 10(2) or 10(4) Salmonella CFU to determine the effects of challenge time on Salmonella cecal colonization. Cecal propionic acid concentrations in two trials increased (P < or = 0.001) within 1 day posttreatment in chicks given PREEMPT, and the increases were indicative of the establishment of the PREEMPT bacteria. Salmonella cecal populations decreased (P < or = 0.001) on average 6 log10 units in these two trials in chicks challenged 4 h posttreatment with 10(4) Salmonella CFU. In a third trial propionic acid did not increase significantly until 2 days after treatment, and there was no decrease in Salmonella colonization when chicks were challenged at 4 h after treatment. However, there were decreases in that same trial when chicks were challenged at 1 and 2 days after treatment. The early establishment of PREEMPT followed by challenges with 10(2) and 10(4) Salmonella CFU resulted in 3% and 3%, respectively, of the ceca testing Salmonella-culture-positive, compared to 28% and 95%, respectively, culture-positive ceca in untreated chicks. The results from this study indicated that in most instances young broiler chicks can be protected against cecal colonization when challenged with 10(2) and 10(4) Salmonella CFU as early as 4 h posttreatment on the day of hatch with the PREEMPT bacteria.

Evaluation of alternative sampling methods for Salmonella critical control point determination at broiler processing.

Several sampling methods have been developed for the detection of Salmonella on broiler carcasses during commercial processing. The present study evaluated three sampling methodologies for sensitivity of Salmonella detection on processed broiler carcasses. Furthermore, the effect of crop removal or chill tank exposure on the frequency of Salmonella recovery was also examined. In two experiments, swab, skin, and carcass rinse samples were compared for sensitivity of Salmonella detection. The results indicated that culture of swabs was less effective (P < 0.05) for Salmonella detection than either skin or carcass rinse samples. No significant (P > 0.05) differences were observed in Salmonella recovery from culture of skin or carcass rinse. In two subsequent experiments, skin and carcass rinse samples were found to be equally sensitive in their ability to detect Salmonella. Additionally, the stages of processing between feather and crop removal were observed to cause significant (P < 0.05) increases in Salmonella recovery within an individual flock. Similar increases (P < 0.05) in Salmonella recovery were also observed following crop removal and immediately following immersion chilling in two separate flocks. These results suggest that culture of skin samples obtained from the thoracic inlet region may be a viable alternative to the traditional whole carcass rinse method for sensitivity of Salmonella detection. Furthermore, these experiments provided some evidence that the majority of Salmonella cross-contamination of carcasses prior to immersion chilling occurred following evisceration, with the chill tank potentially providing a major site for cross-contamination between Salmonella-negative and-positive flocks.

Dosage titration of a characterized competitive exclusion culture to inhibit Salmonella colonization in broiler chickens during growout.

Broiler chicks were spray treated on the day of hatch with titrated dosages (10(6), 10(7), or 10(8) anaerobic CFU) of a characterized competitive exclusion culture (CF3) and challenged orally on day 3 with 10(4) CFU of Salmonella typhimurium. On day 10, cecal contents from control and CF3-treated chicks were cultured for S. typhimurium to determine the minimal efficacious dosage of the CF3 culture. The experiment was repeated in three replicated trials. Resistance to Salmonella cecal colonization was dosage related and progressively enhanced at the 10(7)- and 10(8)-CFU dosages compared with the 10(6)-CFU dosage. The 10(7)-CFU dosage was selected as the minimal effective dosage and evaluated for efficacy during a 43-day broiler growout study. Six hundred broilers were spray treated on the day of hatch and compared with 600 controls. One-half of the control and CF3-treated birds were challenged orally on day 3 with 10(4) CFU of S. typhimurium and designated "seeders." The remaining unchallenged birds were designated "contacts." Compared with the controls, the recovery of Salmonella cells from the ceca of the CF3-treated broilers was significantly decreased (P < 0.01) in the challenged seeders on days 21 and 43 of growout. Salmonella contamination of floor pen litter was significantly reduced (P < 0.05) in pens of CF3-treated birds compared with controls. The transmission of Salmonella cells from seeder to contact birds in the same pens was decreased significantly (P < 0.01). The results indicated that treatment of broiler chicks on the day of hatch with the 10(7)-CFU dosage of CF3 culture effectively increased resistance to S. typhimurium challenge during growout to market age.

Lymphokine-augmented activation of avian heterophils.

Heterophils are important mediators of innate resistance in poultry, especially in young birds that have not yet developed an acquired immune response. Invasion of the intestinal mucosa by Salmonella spp. initiates the recruitment of large numbers of heterophils to the lamina propria. Thus, the heterophilic response can control, but not eliminate, bacterial numbers in the bird until development of acquired immunity. Unfortunately, chicks and turkey poults are highly susceptible to Salmonella infections during the first 4 d posthatch due to the functional immaturity of both the innate and acquired immune systems. We have previously shown that the administration of Salmonella enteritidis (SE)-immune lymphokines (ILK) into either 18-d-old developing embryos or day-of-hatch chicks and poults conferred increased resistance to SE organ invasion. In this review, we present evidence that the protection induced by ILK is mediated by vigorous recruitment and activation of heterophils. These activated heterophils migrate rapidly to the site of bacterial invasion where they phagocytize and kill the SE. Specifically, in vitro studies demonstrate an enhancement of functional activities of the heterophils including chemotaxis, adherence, phagocytosis, and bacterial killing. In addition, during the activation process, membrane expression of adhesion molecules rapidly changes from L-selectins to beta2 integrins (CB11b/CD18) on the cells that become activated. These results further demonstrate the validity of preventive activation in poultry to induce the migration of large numbers of activated phagocytic cells to the site of infection by a pathogenic organism. Importantly, this immunopotentiation of the inflammatory response by ILK, as described here, induces the functional maturation of heterophils during the first 4 d posthatch.

Age-dependent phagocytosis and bactericidal activities of the chicken heterophil.

Chicks are most susceptible to Salmonella infection during the first 4 days post-hatch. In poultry, one of the primary cells in the innate immune response to early bacterial invasion by Salmonella is the heterophil. Previous studies using a granulocytopenic chicken model in more mature birds demonstrated the significant role heterophils have in the defense mechanism against Salmonella. In the past studies have also shown the efficiency of heterophils from 3- to 5-week-old chickens to phagocytose and kill Salmonella as compared to monocytes. During the present study, we investigated the phagocytic and bactericidal activities of heterophils from chickens during the first 7 days post-hatch to evaluate whether decreased heterophil function plays a role in the susceptibility of young chicks to Salmonella infections. Peripheral blood counts demonstrated no differences in the percentages of heterophils during the first week post-hatch. The phagocytic index of the heterophil did not change on day 1 or day 4, but doubled by day 7 (day 1, 30.69; day 4, 33.99; day 7, 60.46). Interestingly, the bactericidal activity of the heterophils from all three age groups efficiently killed Salmonella enteritidis. Based on this data, we conclude that a relationship exists between the age of the chick, the functional activity of the heterophil, and the susceptibility to organ invasion by Salmonella.

Differential expression of adhesion molecules by chicken heterophils activated in vivo with Salmonella enteritidis-immune lymphokines.

Chicken heterophils activated in vivo following the intraperitoneal (i.p.) administration of Salmonella enteritidis-immune T lymphokines (SE-ILK) have been implicated in the protection against SE organ invasion. SE-ILK induces a heterophilia and directly (or indirectly) activates the granulocytes. The invasion of SE provides the secondary signal for directing activated heterophils to the site of bacterial invasion. We examined the mechanism of adherence within the avian heterophil system using an in vitro bovine serum albumin (BSA) matrix in which neutrophil adherence is primarily CD11/CD18 integrin mediated in mammalian systems. Activated heterophils displayed a four-fold increase in receptor-mediated adherence in vitro to BSA-coated slides as compared to control heterophils from PBS-injected birds. The increased adherence of activated heterophils can be partially blocked by either anti-alpha M (CD11b) or anti-beta 2 (CD18) antibodies in a dose dependent manner. Anti-alpha 3 (CD49c) antibody partially blocked adherence of both normal and activated cells. Fluorescence-activated cell scanning (FACS) analysis of the heterophils shows that both control and SE-ILK-activated heterophils collected at 4 h post injection with SE-ILK or PBS display similar amounts of integrin alpha 3 on their surface. This integrin is constitutively expressed and is responsible for the in vitro adherence of both groups. However, antibodies to the Mac-1 complex (CD11b/CD18) block only the adherence of SE-ILK-stimulated heterophils. Thus, the CD11b/CD18 heterodimer is apparently up regulated in response to the injected SE-ILK and plays a major role in the adherence of activated heterophils. Our studies in chickens parallel human and mouse studies showing the importance of the beta 2 integrins in adherence of activated cells.

Frequency of isolation of Salmonella from protective foot covers worn in broiler houses as compared to drag-swab sampling.

In this study we tested the hypothesis that the frequency of Salmonella isolation from protective foot covers worn in individual broiler production houses would compare favorably to isolation rates obtained from conventional drag-swab methods. Salmonella was detected with equal frequency from protective foot covers and drag-swab assemblies on nine individual broiler farms over three separate sampling periods. Salmonella was detected in 13 of a total 27 individual samplings by culturing the protective foot covers, whereas positive detections occurred in 16 of a total 27 samplings when using the drag-swab method. Of the total number of houses identified as positive, these frequencies were unaltered when evaluated against the flock status of each farm at the time of sampling. Both methods were equally as likely to detect Salmonella when houses were either vacant (awaiting the placement of the next flock) or occupied (currently housing chickens of any age). In addition to highlighting the development of a potential new Salmonella monitoring technique, this study reinforces our current understanding regarding the importance of stringent biosecurity practices on poultry farms.

In vitro 14C-amino acid fermentation by CF3, a characterized continuous-flow competitive exclusion culture of caecal bacteria.

Competition for growth-limiting nutrients by broiler caecal bacteria and Salmonella has been suggested as one factor associated with decreased Salmonella caecal colonization. The amino acids arginine, aspartic acid, serine and threonine have been indicated as Salmonella growth-limiting nutrients. Broiler caecal bacteria maintained in a continuous-flow culture (CF3) were used as inoculum for media containing 14C-arginine, 14C-aspartic acid, 14C-serine or 14C-threonine. The 14C-labelled amino acids, except 14C-arginine, were metabolized to lactic, formic, acetic, propionic and butyric acids. In glucose-based media, 72%, 72% and 33% of the radiolabel from aspartic acid, serine and threonine, respectively, were detected in organic acids. Fermentation without glucose resulted in 48%, 50% and 71% of the radiolabel from aspartic acid, serine and threonine, respectively, being detected in organic acids. Results indicated that the early establishment of CF3 in young chicks may result in the depletion of growth-limiting amino acids and, therefore, reduction of Salmonella colonization.

Comparison of drag-swab environmental protocols for the isolation of Salmonella in poultry houses.

Three surveys were conducted during November 1995 and March and May 1996 to compare the use of double-strength skim milk (wet) or no transport media (dry) drag swabs for the detection of salmonellae in 10 broiler houses. Salmonellae were isolated from 57 of 120 individual wet drag-swab samples, compared with 21 of 120 dry drag-swab samples. Furthermore, Salmonella was detected at a higher frequency with wet drag swabs (66.7%) than with dry drag swabs (40%) when compared on an individual growout house basis. A total of seven different serotypes were isolated from the 10 broiler houses. Although double-strength skim milk drag swabs are more labor intensive than dry drag swabs, double-strength skim milk drag swabs are more efficient for detecting Salmonella than are dry drag swabs with no transport media.

Effect of feed withdrawal on the incidence of Salmonella in the crops and ceca of market age broiler chickens.

Previous research regarding Salmonella contamination in poultry has focused predominantly on cecal and intestinal contamination. Recently, the crop has been implicated as an important source of carcass contamination within the processing plant. In the present study, broiler chickens were orally challenged with 1 x 10(8) cfu S. enteritidis at 6 wk of age. At 7 wk of age, birds were randomly divided into two groups consisting of full access to feed, or total feed withdrawal, 18 h prior to sample collection. At the time of sample collection, crops and ceca were aseptically removed and cultured for the presence or absence of S. enteritidis by enrichment. The incidence of S. enteritidis-positive crops was consistently higher (range: 2.8- to 7.3-fold increases) following feed withdrawal than the incidence in samples collected from full-fed broilers in four experiments. Similarly, the incidence of S. enteritidis isolation was consistently higher (range: 1.4- to 2.1-fold increases) in ceca following feed withdrawal than in samples collected from full-fed broilers in these experiments. In a subsequent experiment, ceca and crops were aseptically collected and cultured for the presence of Salmonella immediately prior to or following 8 h feed withdrawal at a commercial broiler house. Similar to the laboratory experiments, the incidence of Salmonella isolation was significantly (P < 0.01) greater from crops following feed withdrawal (36/100) than from samples obtained immediately prior to withdrawal (19/100). However, the incidence of Salmonella in the ceca was not significantly higher following feed withdrawal (31/100) than in samples obtained immediately prior to withdrawal (25/ 100) in this field experiment. These studies indicate that feed withdrawal increases the incidence of Salmonella in broiler crops prior to slaughter and provide further evidence that the crop may be an important critical control point for reducing Salmonella contamination of broiler carcasses.

Neutralization of G-CSF inhibits ILK-induced heterophil influx: granulocyte-colony stimulating factor mediates the Salmonella enteritidis-immune lymphokine potentiation of the acute avian inflammatory response.

Hematopoietic colony stimulating factors (CSF) regulate the growth and development of phagocytic cell progenitors and also augment functional activation of phagocytes. Granulocyte-CSF (G-CSF) is the CSF that acts specifically upon granulocyte progenitor cells and mature granulocytes. We have shown that lymphokines (ILK) from T cells of birds immunized against Salmonella enteritidis (SE) induce a granulocytic (PMN) inflammatory response in chicks challenged with SE. This inflammatory response was characterized by: (a) a dramatic emigration of granulocytic cells from the bone marrow into the peripheral blood, (b) an enhancement of the biological functions of the circulating PMNs, and (c) a directed influx of these activated PMNs to the site of bacterial invasion. In the current study, we determined the presence of G-CSF in ILK by Western blot analysis using a goat polyclonal antihuman G-CSF antibody (Ab). Using this Ab, we then evaluated the role of G-CSF in the ILK-induced protective inflammatory response in chickens against SE. Pretreatment of ILK with the Ab totally abolished the colony-stimulating activity of the ILK. Furthermore, Ab treatment of ILK resulted in: (a) an elimination of the ILK-induced peripheral blood heterophilia with a dramatic inhibition of ILK-mediated protection against SE organ invasion and (b) an elimination of accumulation of inflammatory PMNs in the peritoneum with subsequent decrease in the survival rate of chicks challenged i.p. with SE. Taken together these studies demonstrate for the first time the contribution of G-CSF to avian PMN activation and the immunoprophylaxis of SE infection by ILK in neonatal chickens.

Production and characterization of monoclonal antibodies to a Veillonella species from a continuous-flow culture system of chicken cecal bacteria.

Administering native intestinal flora to newly hatched chicks protects against cecal Salmonella colonization, and is known as competitive exclusion. Continuous-flow culture systems have been used to maintain defined competitive exclusion cultures. We have recently demonstrated that such a stable continuous-flow culture, CF3, contains 29 bacterial strains representing ten genera. Broiler chicks treated with CF3 are protected against Salmonella colonization of the ceca. Such protection is correlated with elevated concentrations of proprionic acid in the cecal contents of treated chicks. In this study we report on the preparation and characterization of monoclonal antibodies to one of the proprionic acid producing anaerobes contained in CF3, namely Veillonella CF3. Five different monoclonal antibodies were characterized with respect to: (1) isotype; (2)Veillonella specificity as judged by cross-reactivity profiles with other bacteria; (3) sensitivity as measured by the limit of detection of the number of colony forming units of Veillonella; and (4) antigen recognition of Veillonella by Western Blot analysis. These antibodies have been used to enumerate Veillonella in both the CF3 cultures and in the ceca of young chicks.

Fermentation and growth response of a primary poultry isolate of Salmonella typhimurium grown under strict anaerobic conditions in continuous culture and amino acid-limited batch culture.

Salmonella typhimurium is a significant hazard to consumer health that is carried asymptomatically in poultry gastrointestinal tracts. Nurmi cultures may prevent Salmonella colonization in young chicks, but the mechanism of competitive exclusion is unclear. Modeling Salmonella's metabolism in pure culture may allow for greater definition in choosing strains for Nurmi cultures. The growth rates and affinity constants of S. typhimurium growing in amino acid-limited conditions were determined in batch culture and compared to primary poultry isolates of cecal strains. Serine and NH4Cl were the best N sources for growth of all organisms tested in this study. The fermentation response of S. typhimurium was also monitored in continuous culture at a slow dilution rate of 0.021 h-1. S. typhimurium was found to adapt to VL media, with trends in protein disappearance, Yglucose, and Yprotein. This may show that amino acid or protein concentrations may be an integral component of the initial establishment of S. typhimurium in the cecum.

Provision of lactose to molting hens enhances resistance to Salmonella enteritidis colonization.

Older leghorn hens, more than 50 weeks of age, were divided into three groups designated 1, unmolted controls; 2, molted; or 3, molted treated with lactose. Forced molt was induced by 14 days of feed removal. Lactose was provided to the hens in group 3 as 2.5% (wt/vol) of the daily drinking water. Each hen in all groups was challenged orally with 10(5) Salmonella enteritidis (SE) cells on day 7 of feed removal. The study was repeated in three replicated trials. The concentrations of acetic, propionic, and total volatile fatty acids (VFA) in the cecal contents of the molted hens in groups 2 and 3 decreased significantly (P < 0.05) on days 6 and 14 of molt compared with the unmolted controls. Forced molt had no apparent effect on pH or on the oxidation-reduction potential of the ceca. Compared to the unmolted controls, SE cecal and spleen and liver colonization was significantly increased (P < 0.05) in the molted hens in group 2. Compared to the molted hens in group 2, SE cecal and spleen and liver colonization was significantly decreased (P < 0.05) in two of three trials in the hens in group 3 provided with lactose. The results suggested that the increased susceptibility of molting hens to SE colonization may be associated with decreased fermentation and production of VFA by cecal bacteria or by a depletion of the number of VFA-producing bacteria present in the ceca. The results further suggest that providing lactose in the drinking water during molting may significantly enhance resistance to SE colonization.