Influence of subclinical virus infections and other factors on broiler flock performance.

1. The influence of subclinical infections with infectious bursal disease virus, adenoviruses, REO viruses and chicken anaemia virus and of various production variables on broiler flock performance was investigated. 2. A significant effect could not be demonstrated of any of the viral infections either alone or in combination. 3. The production results were profoundly influenced by several other factors, that is, breed, diet, stock density and contents of whole wheat grain in the food. 4. The incidence of horizontally-transmitted subclinical chicken anaemia virus infection in Danish broilers has decreased significantly during the period 1988-89 to 1992-93, probably because of improved hygiene and management. The incidence of adeno- and REO virus infections did not change during the same period. 5. It is concluded that factors other than subclinical viral infections presently have an economic impact on performance observed in the Danish broiler production.