Abstract
The objective of the present study was to assess the effective thermal conductivity of the hair coat (k ef, 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 k ef 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 k ef 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 k ef (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.
Highlights
The thermal conductivity of hair coat is related to the structure of a non-homogeneous system (Davis & Birkebak, 1974; Cena & Monteith, 1975ab) constituted by the hairs and the air trapped among them
The metabolic heat generated in the inner body regions is conducted through the hair coat to the atmosphere (a) by free convection in the air among the hairs, and (b) by molecular conduction along the hairs (Davis & Birkebak, 1974)
The effective thermal conductivity of the coat was calculated by assuming absence of air movements, according the system of Cartesian coordinates illustrated in Figure 1 (Davis & Birkebak, 1974)
Summary
The thermal conductivity of hair coat is related to the structure of a non-homogeneous system (Davis & Birkebak, 1974; Cena & Monteith, 1975ab) constituted by the hairs and the air trapped among them. The metabolic heat generated in the inner body regions is conducted through the hair coat to the atmosphere (a) by free convection in the air among the hairs, and (b) by molecular conduction along the hairs (Davis & Birkebak, 1974)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
