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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.

Various attributes of cattle coats are evaluated in terms of their repeatability and heritability, and their capacity to discriminate between coats of different breeds, but principally in terms of their correlations with a subjective coat score, with skin temperature, and with growth rate. The correlation of 0.7 between growth rate and coat score is almost equalled by the multiple correlation between growth rate and a group of measured coat characters. Of these objective characters contributing to coat type, the depth of coat and the hair diameter are most important, followed by the percentage of medullated hairs and the maximum length of fine hairs; hair curvature and follicle angle contribute little. Bonsma's felting score provides a useful indication of coat type, but it is consistently inferior to a coat score. Weight of hair per unit area of skin is unreliable, because it is dependent on length and diameter, which have opposing effects on coat quality. The relative value of different characters varies with circumstances. In late spring, depth was the most important measurement but in winter and early spring it was exceeded in importance by a score of the amount of "body" in the coat. Though coat score is defined fairly completely in terms of component characters, it remains of greater value than any other assessment, presumably because it refers to the whole coat in situ, rather than to a small sample of clipped hair.

A system of subjective scoring of cattle coats, ranging from very sleek to very woolly, is described. It has been applied to about 1600 animals, of which 500 were Hereford and Shorthorn cows and the rest their progeny from matings in four years to British breed and Zebu bulls. Consistency of scoring within and between observers is satisfactory. Highly significant differences between animals of the same breed persist through different seasons. The repeatability of coat score is 0.6 or more over intervals of up to 17 months. Effects of season, age, and sex are described. Heritability of coat score is estimated at 0.63. Coat scores are well correlated with body temperatures and respiration rates. Coat score and post-weaning growth rate of British breed calves are correlated to such a degree that coat score can be superior to a record of body weight as an estimate of growth capacity. The genetic correlation between coat score and growth rate is high in the British breeds. Evidence of the relation between coat score and growth rate in Zebu cross calves is inconclusive. The observed relationships are discussed with particular reference to their physiological causes. The results indicate the potential value of coat characters in selecting tropical beef cattle. The degree to which these results may be applicable to other populations in other environments is discussed. It is concluded that a sleek coat is important in favouring heat dissipation, but it may have even greater significance as an indicator of metabolic efficiency or of capacity to react favourably to stress.

An investigation of the relationships of coat type and coat colour to milk production in the predominantly red Australian Illawarra Shorthorn breed of dairy cattle has been carried out in the Kingaroy district of Queensland. Coat type and shade of red colour were assessed in consecutive years at the beginning and end of lactation and were found highly repeatable. The correlation between each of the scores and milk yield was highly significant. The correlations at the beginning of lactation (r = –0.310**, d.f. = 235, and r = -0.287**, d.f. = 208) were not inferior to those determined at the end of lactation (r = –0.210**, d.f. = 235, and r = –0.336**, d.f. = 225 respectively). Hair diameter determined at the beginning of lactation was positively correlated with milk yield. While these characters are phenotypically correlated with productivity, the extent of their genetic component could not be tested in this investigation.

Twenty-six replicate observations of sweating rate were made on six Hereford x Shorthorn and six Brahman x Shorthorn steers in the field at different times of day and different seasons. Sweating rates were lower in Brahman cross than in Hereford x Shorthorn steers under mild conditions, but higher under stressful conditions. Brahman cross steers increased sweating rate at lower skin and rectal temperatures. Maximum sweating rates were significantly lower in winter than in summer. This is ascribed to an association between sweating function and other aspects of skin function which undergo seasonal changes. Under cool conditions, either there was no consistent difference between animals in sweating rate as in the Brahman cross steers, or the less heat-tolerant animals with higher body temperatures and thicker coat type showed the higher sweating rates. Under challenging conditions of heat, between-animal differences in sweating capacity were revealed and, in the British steers, animals with higher sweating rates then had lower body temperatures. Furthermore, animals with sleek coats showed a higher sweating capacity despite lower thermal stimulus to the skin. The environmental conditions under which sweating capacity is challenged, when differences between animals become important as a component of heat tolerance, depend upon genotype, season, and duration of heat stress.