Experimental cryptosporidiosis in broiler chickens.

Seven-day-old conventional broilers were inoculated either orally or intratracheally (IT) with 2.5 X 10(5), 5.0 X 10(5), or 2.0 X 10(6) oocysts of Cryptosporidium baileyi (32 birds for each dosage level per group; 192 birds total). Thirty-two birds served as unninoculated controls. Mean weekly weight gain and feed conversion were determined during a 5-week period. Carcass pigment was graded using a Roche Color Fan. Fecal oocysts were calculated from random cage samples 6, 8, 11, 13, 15, 18, 20, 22, and 25 days after inoculation (DAI). Effects of C. baileyi on immune responses were examined for Newcastle disease virus-hemagglutination inhibition (NDV-HI) antibody, infectious bursal disease virus-enzyme-linked immunosorbent assay (IBDV-ELISA) antibody titers and delayed hypersensitivity (DH) in half of the birds in each group. Disease or death from cryptosporidiosis did not result from oral inoculation of C. baileyi. Signs of respiratory disease, consisting of rales, sneezing, and dyspnea were observed in all IT-inoculated birds 7 to 21 DAI. Seven deaths occurred in the IT-inoculated groups 14 to 21 DAI. At necropsy, lung parenchyma was gray, firm, and wet in the ventral region. Air sacs contained a foamy, white to gray, mucoid fluid. Histologic lesions in the air sacs and bronchi were epithelial hyperplasia, discharge of mucocellular exudate to the mucosal surface, thickening of the mucosa by cellular infiltrates, loss of cilia, and dilation of mucous glands. Weight gains for IT-inoculated birds were lower (P less than .05) than controls from 14 to 21 DAI, although weight gains for the 5-week period were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)