Latent infections in laying hen farms; experimental infection in farm chickens of various ages
Landgraf, H.; Vielitz, E.
Deutsche Tierärztliche Wochenschrift 90(6): 219-221
1983
ISSN/ISBN: 0341-6593 PMID: 6347614 Document Number: 204755
Fifty apparently healthy hens of different ages, from nine flocks containing several age groups and therefore never depopulated, were introduced into a mycoplasma-free flock of 3650 hens aged 44 weeks and 11 SPF hens. The newly introduced hens from all nine flocks were serologically positive for Mycoplasma gallisepticum, M. synoviae, aviadenovirus and infectious bursitis, but not for adenovirus 127, infectious laryngotracheitis, or reovirus. Birds from two flocks had precipitins for infectious bronchitis virus (IBV). Serological examination of the mycoplasma-free hens before and at 4-week intervals after contact with the infected birds showed at 20 weeks M. gallisepticum antibodies in 17%, M. synoviae antibodies in 53% and IBV precipitins in 10%. The SPF hens developed antibody titres to aviadenovirus and all became serologically positive for M. synoviae and over half for M. gallisepticum. During the 20-week observation period the monthly mortality rate of the exposed flock increased insignificantly from 0.5% to 0.7%, but at 3 weeks the egg production fell from 87% to 69%, along with reduction of egg mass and weight. Both pathogenic and nonpathogenic mycoplasmas were isolated at the end of the experiment from the introduced hens and from the SPF hens. The fall in egg production was attributed to mycoplasma infection.