Serologic incidence of Cryptosporidium in Delmarva broiler flocks.

Banked serum samples collected from an industry-wide serologic survey of eighteen Delmarva broiler flocks conducted in 1985 were evaluated for the presence of Cryptosporidium- specific antibodies in an indirect enzyme-linked immunosorbent assay (ELISA). Evaluation of sera collected at 49-days posthatch showed that 38% of the broiler flocks were serologically positive, whereas 50% of samples obtained from flocks at 63-days during an extended growout were positive. From a performance standpoint, the top nine flocks in the study were essentially negative at the 49-day sampling. In order to more firmly establish the serologic prevalence of Cryptosporidium in Delmarva broiler flocks, a second serologic survey was conducted early in 1987. In this study, an estimated 22% of the 454 broiler flocks sampled at approximately 49 days of age were positive for Cryptosporidium. The negative Cryptosporidium serology in the top 25% of these flocks was associated with better performance, but positive Cryptosporidium serology was not clearly correlated with poor performance. Remarkable differences between Cryptosporidium serologic exposure rates of the growout companies were observed, with some companies having exposure rates as high as 40%, and others rates of less than 3%.