Submitted to: Poultry Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/18/2005
Publication Date: 1/20/2006
Citation: Bouldin, J.G., Buhr, R.J. 2006. Evaluation of egg shell quality of hens infected with salmonella enteritidis by application of compression. Poultry Science. (85):129-135 Interpretive Summary: Transovarian transmission of paratyphoid Salmonella is well documented and occurs at a low incidence in chickens. However, the exact mechanism of follicular invasion is not well understood. The following study investigates the ability of Salmonella to invade ovarian follicles at different stages of follicular maturity in vitro. Ovarian follicles were collected from Leghorn hens and separated into three stages of maturity: 1) large yellow follicles or F follicles (LYF), 2) small yellow follicles (SYF), and 3) small white follicles (SWF). All follicles were incubated at 37°C in RPMI 1640 medium. Follicles were incubated with 1,000,000 CFU/mL of Salmonella Typhimurium and Salmonella Enteritidis sensitive to gentamicin for 2 h. Samples were then removed from the bacterial culture, and placed in medium containing gentamicin sulfate for 5 h to kill any S. Typhimurium or S. Enteritidis which had not invaded the follicular membrane. After the 5 h incubation, follicles were stomached in phosphate buffered saline. Serial dilutions were made of each follicle and viable S. Typhimurium and S. Enteritidis cells were enumerated on brilliant green agar. Two identical trials were conducted. Data suggest that Salmonella may differentially invade ovarian follicles depending on maturity of the follicle, and that SWF may be more susceptible to S. Typhimurium and S. Enteritidis invasion than either the SYF or the LYF.
Technical Abstract: Eggs that were collected from hens that differed by age and/or infection status with Salmonella enteritidis were evaluated for their ability to resist cracking following application of compressive force from an Instron® materials testing machine. Orally infected immature hens produced eggs with significantly decreased hardness units (HU) of shells as compared to a control group (p = 0.01). However, one of three additional infection trials in mature hens resulted in a paradoxical increase in HU following infection and there was no difference in the other two groups. These results support the concept that S. enteritidis can in some circumstances alter avian reproductive tract function at low dose. Compression was overall a sensitive physiological barometer of age, because the average daily hardness units of eggs increased in immature hens (24-wk) in correlation with increasing daily egg production, was maximal in mature hens (29-wk), and then declined in aged hens (59-wk). Other findings in these studies were that (i) excessively low HU (<1.0) were associated with hairline cracks in eggs, which increased from 0.01% from uninfected hens to 0.08% post-infection, (ii) daily egg production significantly increased following infection in both mature and aged hens, and (iii) emaciation was observed in both contact and intravenously infected hens following infection. It may be possible for producers to improve detection of S. enteritidis within flocks by reviewing egg production records for unexpected increases, by observing hens for a low incidence of emaciation, and by increasing the stringency at which eggs are screened for hairline cracks. Compressibility of eggs is a useful approach for analyzing the production cycle of the hen and it may have some experimental application for evaluating how different strains of S. enteritidis alter avian reproductive tract function.