Effects of a hot climate on the performance of first lactation Holstein cows grouped by coat color.

ABSTRACT

Dairy Herd Improvement data from 432 Holstein cows were analyzed to determine if coat color was a significant source of variation in the performance of first lactation cows in a hot climate. One of three coat color scores was subjectively assigned to first lactation Holstein cows. White coat color was less than 40% black (15% of the cows), mixed coat color was 40 to 60% black (42% of the cows), and black coat color was greater than 60% black (43% of the cows). Coat color by season of freshening interaction was not an important source of variation for any of the production traits studied; but cows were cooled during the first 130 d of lactation, perhaps removing any advantage white cows may have had during the summer months. The interaction between coat color and season of freshening was significant for days open and services per conception. White cows freshening in February and March required fewer services per conception and had fewer open days than the mixed and black cows. The heritability estimate of coat color was .22 using a paternal half-sib analysis. Additional studies, with more white cows represented, would be useful to elucidate the effects of coat color on production in a hot climate.