a1 Division of Animal Genetics, CSIRO, Tropical Cattle Research Centre, Rockhampton, Qld 4700, Australia
Data on incidence and severity of infection with bovine infectious keratoconjunctivitis and proportion of eye margin pigmentation were collected over 3 years in a mixed herd of Hereford × Shorthorn (HS), Africander x HS, Brahman x HS, grade Africanders and purebred Brahmans. Both sexes were scored at 3 and 8 mo but only females were scored at 15 mo. At all ages, the incidence of infection was greatest in the HS and lowest in the Brahmans in which no infections were recorded. The severity of infection and proportion of bilateral infections were also greatest in the HS animals.
Infected animals were lighter at all ages than comparable uninfected animals. HS females which showed signs of infection at each age were 22·8 kg lighter at 15 mo than those which had never shown signs of being infected. The magnitude of the weight difference was directly related to the severity of infection.
In the HS breed, both the incidence and severity of infection were related to the proportion of eye margin pigmentation. At 15 mo, 68% of HS females with full eye margin pigmentation were infected compared to 96% of comparable unpigmented animals. At 15 mo infected HS females with full eye margin pigmentation were heavier than unpigmented contemporaries. It was concluded that the lower weight of infected animals was primarily the result of the disease rather than vice versa.
(Received January 21 1975)