Ontogeny of delayed hypersensitivity in young turkeys

Variation in toe-web response of turkey poults to phytohemagglutinin-P and their resistance to Escherichia coli challenge

One thousand 5-wk-old male turkeys from each of two commercial strains (A and B) were grouped into low, medium, and high responders based on the cutaneous basophil hypersensitivity (CBH) response obtained 24 h after toe-web inoculation with 100 micrograms of phytohemagglutinin-P (PHA-P). The CBH response for Strain A was higher than strain B (P = 0.00001) and ranged from 0 to 1.95 mm, with a mean of 0.66, whereas the CBH response for Strain B ranged from 0 to 1.67 mm with a mean of 0.38. At 6 wk of age, 36 birds from each of the six response groups were inoculated into the left thoracic air sac with 1.5 x 10(7) cfu of an early log phase broth culture of Escherichia coli. Samples of 5 or 10 birds were necropsied from each of the six groups at 7, 14, 28, and 42 d postinfection (PI). Birds were scored for air-sacculitis/pericarditis (AS) and turkey osteomyelitis complex (TOC). Overall mortality of birds inoculated with E. coli was 31%. There were no mortalities in unchallenged controls. Strain A had significantly higher Week 1 mortality, marginally higher overall mortality (P = 0.1), and higher AS scores than Strain B. There were no TOC lesions detected until 7 d PI, after which all mortalities had TOC lesions in multiple sites. The differences in CBH response within each strain were not clearly correlated to E. coli susceptibility. However, these data suggest that air sac inoculation of E. coli can provide a useful model for the study of TOC. The greater incidence of disease in Strain A indicates that an enhanced inflammatory response may increase susceptibility to E. coli septicemia.