Reduction of horizontal transmission of avian leukosis virus subgroup J inbroiler breeder chickens hatched and reared in small groups

Transmission of avian leukosis virus, subgroup J (ALV-J), from donor chicke ns inoculated as embryos to simulate congenital infection to uninfected hat chmates was studied in two strains of commercial broiler breeder chickens. Chicks of two commercial lines free of ALV-J became infected when hatched ( 1/2 lots positive) or reared (8/8 lots positive) in direct physical contact with ALV-J-infected donors. Infection also occurred when chicks were expos ed in the hatchery to ALV-J-infected donors by cloacal swab transfer (2/2 l ots positive), needle transfer during subcutaneous inoculation (2/2 lots po sitive), or ingestion of infected meconium (2/2 lots positive). However, tr ansmission was delayed or prevented by wire partitions in the hatcher and r earing of small groups in cubicles, and rarely (1/10 lots positive) resulte d from short-term direct or indirect contact. In a simulated field test, a flock of 503 broiler breeder chickens with an initial embryo infection rate of 4.6% was hatched and reared as 48 small groups to 4 weeks of age. Group s were tested at hatch and at 3 weeks, and 14 infected groups were eliminat ed. This flock tested negative for ALV-J infection from 4 to 32 weeks and d id not transmit infection to progeny or develop tumours. A control group of 377 chickens with a similar initial infection rate was hatched and reared as a single group. This control flock transmitted virus to 5.7% of its prog eny and about 5% of the hens developed tumours. The small-group hatching an d rearing practices employed in these studies allowed for the accurate iden tification and removal of groups containing chickens infected prior to hatc hing and prevented horizontal transmission of ALV-J between uninfected and infected groups for at least 4 weeks. More importantly, application of thes e procedures successfully eradicated ALV-J in a single generation under lab oratory conditions. This suggests that similar procedures could be a valuab le adjunct to virus eradication programmes in the field.