Occurrence of subgroup J avian leukosis virus in Taiwan

There are three grandparent farms for three different chicken breeds in Taiwan. One of these farms, populated by breast meat yield chickens (yield type), suffered from a severe subgroup J avian leukosis virus (ALV-J) infection in mid-1997. The affected flocks at that farm had a weekly mortality of more than 1% and a 15% drop in egg production. The broilers from that breed had a 10% condemnation rate during the first week of age, and 5% of the remaining broilers were stunted afterwards. Some chickens had myeloid leukosis lesions at 6 weeks old. Their survivability was about 85%. However, chickens at the other two grandparent farms, populated with non-yield chickens (regular type), were also infected by ALV-J and showed myeloid leukosis. However, chickens at these farms produced progeny whose survivability reached more than 95%. ALV-J caused greater economic loss in yield type chickens than in regular type chickens in Taiwan.