An in-depth diagnostic investigation of poor performance on a broiler ranch

The initial purpose of this investigation was to document nonuniformity and poor performance that had reportedly occurred in several successive grow-out flocks on a commercial broiler ranch in California. Previous sporadic necropsy submissions of birds to the diagnostic laboratory resulted in reports of Escherichia coli septicemia, reovirus isolations from joints, and adenovirus isolations from livers. Intranuclear virus inclusion bodies had been detected in the liver of 1 bird from 1 submission. Therefore, an in-depth diagnostic investigation of the birds sampled weekly from each house on the ranch was undertaken to establish the role of these and other potential pathogens in the forthcoming flocks. Partway through the investigation, histopathology indicated the flock had a bursal disease problem. Polymerase chain reaction analysis of bursal tissues was performed on selected samples. An infectious bursal disease virus (IBDV) strain different from that used in the vaccine was detected in the bursas by reverse transcription-polymerase chain reaction-restriction fragment length polymorphism. This IBDV strain had sequences across the hypervariable VP2 region, which is identical to the T1 strain except for 1 position. The weight gains, recorded and averaged at wk 5 and 6 according to the producer's management plan, were within the producer's standard expectations. Although reovirus and adenovirus were isolated and rotavirus-like particles were noted in pooled intestinal samples on examination by electron microscopy, little significance was attributed to these agents because the agents were detected from healthy birds. Identification and documentation of involvement of this T1 strain of IBDV was facilitated by weekly diagnostic submissions from all the houses on the ranch.