R. Bras. Zootec.01/Nov/2009;38(11):2218-23.
Effective thermal conductivity of the hair coat of Holstein cows in a tropical environment
DOI: 10.1590/S1516-35982009001100022
The objective of the present study was to assess the effective thermal conductivity of the hair coat (kef, mW.m-1.K-1) of Holstein cows in a tropical environment, as related to conduction and radiation in the absence of free convection. The average kef was 49.72 mW.m-1.K-1, about twice the conductivity of the air (26 mW.m-1.K-1) and much less than that of the hair fibres (260 mW.m-1.K-1). The low kef values were attributed mainly to the small cross area of individual hairs, ρef/ρf (17.2% and 21.3% for black and white hairs, respectively). White coats were denser, with longer hairs and significantly higher kef (53.15 mW.m-1.K-1) than that of the black hairs (49.25 mW.m-1.K-1). The heritability coefficient of the effective thermal conductivity was calculated as h2=0.18 the possibility was discussed of selecting cattle for increased heat transfer through the hair coat.
Keywords: hair coat; Holstein cows; thermal conductivity