Coat Characters of Cattle in Relation to Adaptation

It is a familiar observation that different ecotypes of cattle, whether they are distinguished as species, breeds, or strains, show marked contrasts in coat cover. These differences follow the principle, dignified by Wright (1954) as “Wilson’s Rule”, of a gradient from thick, woolly coats in cold climates to short coats with bristly hairs lying sleekly against the skin in hot climates. The contrasts between British Highland cattle or Scottish beef breeds and the Zebus of India or Bantengs of south-east Asia clearly represent adaptations to cold and to heat. Within breeds, also, climate modifies both phenotype and genotype of coat characters. For instance, progeny of a N.S.W. strain of Herefords, born and reared in Central Queensland, had longer coats than progeny of a Central Queensland strain (Turner and Schleger 1960). The fact that coat genotype seems to have changed fairly rapidly in breeds introduced to the tropics confirms the importance of this trait to adaptation. Individual animals also grow shorter coats when transferred from a cold to a hot environment, even at the same latitude (Berman and Volcani 1961), unless their limits of general adaptation are exceeded, when physiological degeneration sets in and a woolly, non-shedding coat is produced. The effect of coat cover on body temperature regulation has been shown by clipping (Yeates 1955, Berman and Kibler 1959, Bianca 1959, Dowling 1958, 1959b, Turner 1962). This kind of demonstration is only a first step. It does not put in perspective the importance of inherent differences in coat type, and it also leaves one to assume how much a difference in body temperature control under test conditions affects total physiological and economic performance in the field. Bonsma (1949) showed the direct relationship between inherent coat type and capacity to thrive in the Northern Transvaal. Dowling (1956) associated the heat tolerance and performance of different strains of cattle with their coat characters, and Turner and Schleger (1958, 1960) measured the degree of variability of coat type within herds, and assessed the proportion of the variation in growth rate that is accounted for by variation in coat type. We found that, within herds of Herefords or Shorthorns, variation in coat type accounted for about one third of the variation in growth rate. The correlation between coat type and gain was higher than the repeatability of gain so that assessment of coat type was superior to a record of gain as an estimate of growth