The prevalence of Salmonella species in commercial layer chicken in Namakkal poultry zone of India was investigated. Samples collected from 6572 dead birds of 85 farms during necropsy were screened for the presence of Salmonella species by cultural examination and two farms were positive for Salmonella enterica organisms and identified as Salmonella typhimurium in serotyping. The S. typhimurium isolates were amplified in polymerase chain reaction (PCR), and produced two fragment sizes viz. 363 bp for kpnI gene and 497 bp for Pef A gene. The prevalence of S. typhimurium in commercial layer farms in Namakkal area was estimated as 2.35%. Feed and fish meal was found contaminated with S. typhimurium and Clostridium perfringens and acted as source of infection in the positive flocks.  The age of layer chicken of the affected farms were 24 and 30 wk with a morbidity of 3 and 4%, drop in egg production of 2 and 3% and mortality of 0.5 and 1%, respectively. On necropsy examination ovaries were congested, misshapened and oviduct serosal blood vessels were congested and mucosa contained albuminous material in 65% and cheesy plugs in 35% of the 17 positive birds. Histopathologically, decreased villi height and inflammatory changes in intestine and infiltration of inflammatory cells in ovaries and necrosis, infiltration of inflammatory cells and granulomatous reaction in the different regions of the oviduct were noticed. It was concluded that supplementation of contaminated fish meal in poultry feed could be the source of Salmonella infection in commercial layer flocks.

Key words: Characterization, Layer, Pathology, polymerase chain reaction, Prevalence, Salmonella