Z R Howard

United States Department of Defense, Arlington, Virginia, United States

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Publications (9)

  • [Show abstract] [Hide abstract] ABSTRACT: Foodborne illness caused by Salmonella spp. is a worldwide problem. In the United States Salmonella Enteritidis is the second most commonly isolated serotype from human illness, and is known to be strongly associated with shell eggs and egg containing products. Eggs can become contaminated internally either by penetration through the shell or directly during formation in the reproductive tract. This review begins with a brief account of the physiology of egg production and the various physical and chemical barriers the egg possesses to prevent bacterial contamination. Factors involved in vertical and horizontal transmission of S. Enteritidis are examined, as well as the role of forced molt in colonization of the hen. Pre- and post-harvest mitigation strategies are also discussed.
    Article · Mar 2012 · Food Research International
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    [Show abstract] [Hide abstract] ABSTRACT: Since one of the costs in the commercial egg industry is that of replacement pullets, commercial egg layer managers have opted to induce molt older hens in order to extend their productive life for additional egg laying cycles. Conventional molt induction involves the complete removal of feed for several days. However, this management practice can lead to deleterious physiological responses by the hen and subsequent susceptibility to infection by pathogens. Consequently less stressful molting regimens involving the feeding of low energy diets such as alfalfa have been developed. In this study, 80 week old laying hens that were deprived of feed or fed alfalfa meal during a nine day induced molt. Full fed hens were used as the control. On day 8 serum triglycerides were quantified and on day 9 hens were euthanized and the liver, spleen, heart, intestine, pancreas, ovary, and kidney were collected and weighed. Intestinal weight were highest in the non-molted hens, lower in the hens fed alfalfa, and lower still in the hens deprived of feed. Molted hens exhibited reduced weights of liver, heart, ovary, and pancreas compared to the non-molted hens. Serum triglycerides were highest in the non-molted hens, less in feed deprived hens, and the lowest in alfalfa fed hens. These results suggest that a comparable molt could be achieved with feeding alfalfa meal to 80 week hens compared to feed deprivation.
    Full-text Article · Oct 2008 · Bioresource Technology
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    [Show abstract] [Hide abstract] ABSTRACT: The practice of induced molting involves the restriction of light, feed removal and optionally water for 5-14 days. However, there is growing concern regarding feed removal and animal welfare issues. With this in mind, alternative diets have been developed to produce similar molting effects as that of feed deprivation. Alfalfa, which largely consists of insoluble fiber, can be used as a molting diet. In this study, heterophil and lymphocyte counts, serum chemistry, and organ weight parameters were evaluated in hens that were deprived of feed or fed alfalfa during a nine day induced molt. Full-fed hens were used as the control. Blood serum parameters assessed included calcium, magnesium, glucose, total protein, ketone bodies, uric acid, and cholesterol. White blood cells were counted and categorized by cell type. On the ninth day of the trial, the hens were euthanized and the liver, spleen, heart, intestine, pancreas, ovary, oviduct, and kidney were collected and weighed. On day 8 birds molted with alfalfa or by feed deprivation had significantly higher (P<0.05) levels of ketone bodies and cholesterol and lower levels of calcium, and magnesium compared to the full-fed hens while birds molted by feed deprivation exhibited significantly lower levels of uric acid. Birds molted by both methods exhibited significant reductions in ovary, oviduct, liver and pancreas weights and increased spleen weights when compared to the non-molted hens. On days 0, 2, and 6 there were no significant differences (P>0.05) in either heterophil or lymphocyte percentages. However, heterophil percentages were higher in feed withdrawal birds than full-fed birds on day 4 but lymphocyte percentages were higher in full-fed birds compared to feed withdrawal birds. On day 8 of the induced molt lymphocyte percentages were higher from full-fed birds when compared to feed withdrawal birds but no significant differences were detectable for heterophil percentages. Based on reproductive organ weight loss and changes in serum and immunological responses of birds during molt, it appears that alfalfa meal can be an effective molt induction alternative.
    Full-text Article · Feb 2008 · Bioresource Technology
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    Z R Howard · Moore R.W · I.B. Zabala Diaz · [...] · Ricke S.C
    [Show abstract] [Hide abstract] ABSTRACT: An in vitro study was designed to determine the extent of Salmonella enterica serovar enteritidis survival and growth permissiveness in egg components isolated from shell eggs held at refrigeration temperature over an 8 week time period. Eggs were collected from a commercial laying facility at one-week intervals for eight weeks and stored at refrigeration temperature. After storage, eggs were dipped in ethanol, cracked aseptically and separated into yolk and albumen samples. S. enteritidis resistant to novobiocin and nalidixic acid were inoculated on to the surface of the yolk membrane at a concentration of approximately 106 CFU mLˉ1. Yolks were then covered with albumen and incubated for 24 hrs at 25ºC. After incubation, eggs were separated into component parts. Samples were removed from yolk, albumen and yolk membrane and diluted 10-fold in sterile phosphate buffered saline. In albumen, S. enteritidis counts were increased in weeks 3 and 8 compared to week 1 (trial 2). The frequency of eggs exhibiting net growth of S. enteritidis in albumen occurred at week 7 versus weeks 0 and 1 in trial 1 and weeks 3 and 8 versus weeks 0 and 2 in trial 2. In the membrane fraction, the frequency of eggs exhibiting net growth of S. enteritidis occurred at weeks 5 and 8 versus week 0 in trial 2. In the yolk fractions, S. enteritidis counts recovered from week 6 eggs were significantly higher (P<0.05) than those of weeks 0, 2, 3 and 7 (trial 2) and the number of detectable S. enteritidis positive eggs were greater in week 8 than week 5 in trial 1. This suggests that egg components recovered from aged eggs stored at refrigeration temperatures infrequently supported S. enteritidis net growth but generally did not inhibit survivability.
    Full-text Article · Feb 2007 · American Journal of Agricultural and Biological Science
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    Z R Howard · L M Donalson · W K Kim · [...] · S C Ricke
    [Show abstract] [Hide abstract] ABSTRACT: Because food and poultry industries are demanding an improvement in written communication skills among graduates, research paper writing should be an integral part of a senior undergraduate class. However, scientific writing assignments are often treated as secondary to developing the technical skills of the students. Scientific research paper writing has been emphasized in an undergraduate course on advanced food microbiology taught in the Poultry Science Department at Texas A&M University (College Station, TX). Students’ opinions suggest that research paper writing as part of a senior course in Poultry Science provides students with scientific communication skills and useful training for their career, but more emphasis on reading and understanding scientific literature may be required.
    Full-text Article · Mar 2006 · Poultry Science
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    Z. R. Howard · R. W. Moore · I. B. Zabala Diaz · [...] · S. C. Ricke
    [Show abstract] [Hide abstract] ABSTRACT: Salmonella enterica serovar Typhimurium has been isolated from commercial egg production facilities in the United States. Given its importance as a causative organism for foodborne salmonellosis, identifying approximate timelines for bacterial invasion of the egg is needed. The objective of this study was to examine net growth of S. Typhimurium in egg components over time. In trial 1 eggs were collected over a 24 hour period from a flock of single comb white leghorn hens while in trial 2 eggs were picked up from a commercial laying source once a week over the course of eight weeks and stored. Eggs were held at refrigeration temperature and each week, subsets of eggs were cracked, separated into yolk and albumen components, and inoculated with 108 CFU/ml of novobiocin and nalidixic acid (NO/NA) resistant S. Typhimurium onto the vitelline membrane of the egg. Yolks were then covered with albumen. Eggs were incubated for twenty-four hours at 25°C. After incubation eggs were again separated into albumen, yolk, and vitelline membrane samples. In trial 1, S. Typhimurium net growth occurred in albumen by the second week and continued from 4 to 8 weeks while in trial 2 net growth only occurred at week 5 and 7. S. Typhimurium net growth on vitelline membranes occurred by 2 weeks and continued from 4 to 8 weeks in trial 1 while no net growth occurred in trial 2 over the 8 week period. Yolk samples showed no net increases in S. Typhimurium populations over the 8 week period.
    Full-text Article · Feb 2006 · Journal für Verbraucherschutz und Lebensmittelsicherheit
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    Z.R. Howard · R.W. Moore · I.B. Zabala-Diaz · [...] · S.C. Ricke
    [Show abstract] [Hide abstract] ABSTRACT: 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 degrees C in RPMI 1640 medium. Follicles were incubated with 1 x 10(6) 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.
    Full-text Article · Jul 2005 · Veterinary Microbiology
  • K.L. Landers · Z.R. Howard · C.L. Woodward · [...] · S.C. Ricke
    [Show abstract] [Hide abstract] ABSTRACT: Dietary molt induction to initiate additional egg laying cycles in commercial laying hen flocks is a wide spread practice in the United States. Feed deprivation is the most commonly used method but this practice has generated several concerns which has lead to research for viable alternative approaches. From a management standpoint a single ingredient molting diet consisting of high fiber-low energy represents an easily adaptable diet for large laying hen production units. Alfalfa meal is readily available in most commercial locations and possesses many of the desirable properties of an ideal laying hen molt diet. In the current study hens at a commercial laying facility were molted by both alfalfa and feed deprivation. After the hens had reentered post-molt commercial egg production, eggs were examined for egg quality performance. Egg shell strength, albumen height, yolk height, weight, length, and yolk color were all tested using various mechanical techniques. The eggs were also sampled for testing by consumer sensory panels that assessed the desirability of the eggs' color and flavor/texture. Eggs laid by hens molted by alfalfa had a significantly lower (p<0.05) "a*" level of colorimetry. Eggs laid by hens molted with alfalfa also exhibited significantly higher (p<0.05) egg weights and length. In the consumer sensory test, there was no significant difference (p>0.05) in color or flavor/texture scores in eggs from either feed deprived or alfalfa molted hens. The consumer sensory and mechanical quality attributes indicates that alfalfa shows promise as an alternative molt induction diet by providing a single diet option for extending egg production into a second egg laying cycle.
    Article · Jun 2005 · Bioresource Technology
  • Zoe R. Howard
    [Show abstract] [Hide abstract] ABSTRACT: In recent decades salmonellosis has been on the rise as a food related illness worldwide. Causing over 24% of all non-typhoidal Salmonellosis cases, SE is the most frequently isolated serovar of Salmonella. Increased isolation of SE from eggs has paralleled an increase in the number of transovarian infections associated with laying hens in the poultry industry. This route of infection is a fairly new line of study when compared to the more traditional path where SE originates from fecal contamination through the shell. Salmonella Typhimurium (ST) is another concern for the egg industry. ST has caused 23.5% of all non-typhoidal salmonellosis cases. Understanding these two egg pathogens requires an in depth look at the mechanisms by which an egg may support infection and bacterial growth. Eggs were inoculated with both SE and ST onto the vitelline membrane and incubated for 24 hours. It was hoped that by gathering samples from the interior of the egg membrane, the albumen of the egg, and the membrane itself, some clarification as to when Salmonella is allowed to grow within the egg could be gathered. Albumen and membrane were found to be more hospitable environments to bacterial growth with increased storage times. In order to better understand the movement of bacteria into pre-ovulatory tissues, samples were gathered from mature laying hens. Follicular tissues were separated into divisions based on maturity, and bacteria were added to an in vitro cell culture broth containing the follicles. The point of this experiment was to determine if either species of Salmonella preferentially moved into follicles of different maturity when inoculated in vitro. A third experiment looked into the role of developmental stages of the vitelline membrane in exclusion of bacteria from the nutrient rich yolk. Tissues were gathered in the method described above. The follicular sack was removed from half of these samples and left intact for the other half. Another treatment group included was the yolks of eggs which had been laid by the same flock of birds. Results showed that follicles with intact follicular sacks were more susceptible to bacterial colonization than other treatment groups.
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