Infectious bovine keratoconjunctivitis: isolation of Moraxella bovis from two groups of young beef cattle in fly control field trials during 1981.

The rate of infection with Moraxella bovis was determined for two herds of calves during the course of a year. High infection rates with the haemolytic variant were found in the herds while they were housed during their first winter but this infection rate fell steadily after turnout. A rise in infections with the non-haemolytic variant was observed during this time. The animals remained free from clinical infectious bovine keratoconjunctivitis during the summer, unlike similar groups of animals in previous years. Immunity, weather and flies are considered for their possible relevance to this observation.