Age of challenge is important in Salmonella Enteritidis studies in pullets and hens: a systematic review

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ABSTRACT Nontyphoidal serovars of Salmonella enterica subsp enterica frequently colonize the intestinal tracts of chickens, creating risks of contamination of meat and egg food products. These serovars seldom cause disease in chickens over 3 weeks of age. Colonization is generally transient but can continue to circulate in a flock for many months. Vaccination of breeders and layers is the most effective method of control of infections with serovars Enteritidis and Typhimurium, and the development of these vaccines or other preventative treatments requires challenge studies to demonstrate efficacy. However, establishing a successful challenge model where the control birds are colonized to a sufficient extent to be able to demonstrate a statistically significant reduction from the vaccine or treatment is problematic. A meta-analysis of published S. Enteritidis challenge studies was performed to pursue the best challenge model conditions that provide consistent control colonization outcomes. Challenge at sexual maturity was significantly more effective in achieving at least 80% colonization of control hens. RESEARCH HIGHLIGHTS Salmonella challenge chicken models do not always achieve high colonization levels in controls. The age of hen is important in achieving good caecal colonization. Challenge around sexual maturity provides the best control colonization outcome. A challenge dose rate of 105 CFU/ bird is adequate in birds under 30 weeks of age.