RESUMEN
Social aggregations of three cattle breeds and crosses between them were studied under controlled conditions at a Brazilian research station. Cows raised with animals of their own breed in isolation from other breeds maintained segregated social groups. Cattle of the same breed raised apart formed aggregations based more on familiarity than on genetic communality. There were breed differences in both of those tendencies. Hybrids were no more likely to associate with cattle with which they had one breed in common than with animals of completely different breeds, although having two breeds in common increased the likelihood that hybrids would be found together. Recently weaned calves did not assort themselves by shared kinship, but they formed phenotypic groupings correlated with color. In the absence of familiar individuals, cattle may use familiar phenotypes in establishing social preferences and cohesive herds.