Physiological attributes of coat colour in beef cattle

A system of scoring coat colours in the range from light red to dark red has been applied to cattle at the National Cattle Breeding Station, Rockhampton, Qld. The cattle were Herefords and Shorthorns and crosses between these and the Africander. Colour is affected by age, season, reproductive stake, growth phase of the coat, and sex, and also by exposure to solar radiation. Colour is a highly repeatable characteristic of individual animals and has high heritability, estimated at 53%. Melanin concentration in the hair is the chief determinant of colour, the partial regression coefficient (β) being 0.73, while the proportion of medullated hairs (β = –0.32) and the mean diameter (β = 0.17) have half and quarter the significance respectively. The relationship between coat type and coat colour is complex, varying with the season of the year. Within the range of red colours studied, there is no tendency for darker animals to exhibit any effects of higher heat load. The relationship between depth of colour and body temperature tends if anything to be slightly negative, which suggests that darker animals have some other characteristic favouring temperature regulation. Correlations between intensity of red colour and rate of gain are consistently positive. The magnitude of the relationship varies with season, and the validity of choosing an optimum season is discussed. The mean correlations between gain and colour score in the optimum period are 0.50 for Africander cross and 0.32 for British breed calves. Coat colour may therefore be more useful than a score of coat type in Africander cross calves, though less useful in British breed calves.