July 2000

Project # 365
Poultry House Ventilation and Humidity Moisture Control:
Reduction of Salmonella and E.coli Counts on Broiler and Layer Farms

Sam W. Joseph, Ph.D.
Department of Cell Biology and Molecular Genetics
Roberta A. Morales, D.V.M.,Ph.D.
Virginia-Maryland Regional College of Veterinary Medicine
University of Maryland
College Park, MD 20742

"Importance of Ventilation in Control of Salmonella and E.coli"

By determining the numbers of bacteria in the poultry production environment, improved air ventilation was identified as a prime management practice in preventing "hot spots" of Salmonella and E.coli multiplication in broiler litter or layer manure.  The prevention of water leakage was also identified as another important flock health and quality assurance practice.

The study further corroborated: 1) the relationship between litter/manure humidity and moisture control with the reduction of Salmonella contamination on farms; and 2) that contamination is not uniformly distributed throughout the house but instead, is mainly located in areas that are favorable for bacterial multiplication.  A variety of ventilation options are proposed to ensure that air is gently and uniformly distributed at the velocity of 100 feet or more per minute over and in close proximity to all litter and manure surfaces to achieve drier litter/manure and healthier, safer birds.

In this study, the numbers of Salmonella and E.coli in litter/manure related to low levels of humidity (relative humidity of Aw) and moisture content (MC).  Drag swabs and individual litter cultures confirmed that high Aw levels (>90 percent) were associated with a higher prevalence of Salmonella if introduced, and E.coli.  Furthermore. culture of litter revealed higher Salmonella populations in litter samples possessing MC levels above 35 percent and Aw values ranging from 0.9 to 0.95.

Additionally, a quantitative direct relationship between ventilation rates and higher or lower levels of humidity and moisture in poultry litter/manure and Salmonella/E.coli loads in the litter was observed.  Very low litter surface airflow rates (<60 feet/minute) tended to be associated with higher E.coli counts in broiler litter as opposed to elevated airflow rates (>60 fpm), which were associated with reduced E.coli populations.  A clear cut trend for Salmonella was not established for broiler litter due to the large number of Salmonella negative samples.  However, clearly higher Salmonella counts were observed in layer manure pits away from the fans with very low airflow rates.  For those commercial broiler houses surveyed, decreased airflow was significantly associated with high MC (av. 41.2 percent) and Aw (av. 0.909).  Conversely elevated airflow was associated with lower MC (av. 29.6 percent) and Aw (av.0.849).

In laboratory studies on the persistence of Salmonella in litter, used poultry litter was seeded with Salmonella typhimurium, thoroughly stirred, stored at room temperature and tested weekly for Salmonella. Salmonella persisted through the seventh week in the litter by usual culture methods.  From eight to 10 weeks, the organism was only isolated by the delayed secondary enrichment procedure, suggesting that Salmonella may survive in the litter in reduced numbers.  In a second laboratory study, we were unable to verify that Aw levels play a vital role in the survival and multiplication of Salmonella.

This study suggests that elevated water parameters (Aw 0.9 to 0.95 and MC above 35 percent) may aid in the persistence of and promote large Salmonella and E.coli populations in poultry houses.  Modest improvements in ventilation that ensure all little/manure surfaces have an airflow rate >100 feet per minute may be important in maintaining drier litter/manure, thus creating an adverse environment for the growth of food -borne pathogens.

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