IMMUNE SUPPRESSION OF COMMERCIAL BROILERS IN CROATIA, SLOVENIA, AND BOSNIA AND HERZEGOVINA FROM 1981 TO 1991

A continuous decline in immune responses to Newcastle disease (ND) vac cine was observed in commercial broiler flocks in Croatia, Slovenia, a nd Bosnia and Herzegovina beginning in 1982, Floating mean haemaggluti nation inhibition (HI) titres declined from log(2) 4 in 1983 to a low of log(2) 2.4 in 1986, then were log(2) 2.9 in 1990. Several causes of the decline were discounted, leaving mycotoxins in feed and infection with chicken anaemia virus (CAV) as the two most likely causes. Mycot oxins in feed could not be evaluated retrospectively, but archival tis sues were available from Croatia and Slovenia. Tissue sections were ex amined by in situ hybridization for CAV. Whereas only one chicken from early in the decade was infected, all but one of the chickens from la te in the decade were. The increase in CAV detection correlated invers ely with ND HI titres. Whereas this correlation does not establish cau se and effect, CAV cannot be eliminated as a contributory cause of imm une suppression.