Broiler production is highly dependent on good health in the parent flocks. The so-called normal mortality in these flocks remains to be addressed to further reduce mortality of the breeders and to improve the quality of broilers. The aim of the present study, therefore, was to investigate the etiology of this breeder mortality to map out possible critical periods during production in relation to possible risks of importance to the offspring. Dead birds from four flocks were subjected to postmortem and bacteriologic examination from onset of lay until slaughter (20-60 weeks). Causes of mortality were divided into noninfectious and infectious etiology. The infectious group could be subdivided into suppurative salpingitis/peritonitis caused by and other infections (e.g., sepsis, endocarditis, and arthritis) mainly caused by Gram-positive cocci. Data analysis showed that 41% of the birds died from noninfectious causes, while 55% died from infectious causes, and 4% had no known cause of death. The prevalence of noninfectious mortality was highest in the youngest birds and lowest in the oldest birds. In contrast, the infectious mortality was lowest in the young birds and highest at the end of production. Within each age group, the prevalence of salpingitis/ peritonitis was 26% in young birds (20-29 weeks) and progressed throughout production to 41% in the oldest birds (≥50 weeks of age). Mortality due to other infections was low at onset of production (12%), peaking at 40-49 weeks of age (25%). Consequently, 40-49 weeks of age is identified as a critical period with regard to causes of mortality, possible vertical transmission of to the offspring, and increased risk of Gram-positive coccal infections.
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