Effective thermal conductivity of the hair coat of Holstein cows in a tropical environment

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, ρ ef /ρ f (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 h 2 =0.18 the possibility was discussed of selecting cattle for increased heat transfer through the hair coat.

Thermoregulatory responses related to coat traits of Brazilian native ewes: an adaptive approach

“…Animals that showed lower NH may lead less difficulties for eliminating latent heat via cutaneous evaporation (Holmes 1981), and shortest coats (HL) also is considered as favourable for heat exchange. The coat traits are studied to analyse adaptation of animals (Maia et al 2009;McManus et al 2009;Helal et al 2010). This declining in thyroid function during heat stress may be due to the effect of heat on hypothalamic pituitary axis to cause reduction in thyrotropin-releasing hormone, which enable the animal to reduce basal metabolism (Johnson 1987).…”

“…The T 4 hormone plays an important role in livestock productivity (Todini et al 2007). By contrast, when the animals had coat traits that makes heat loss difficult, such as longer hair and higher hair density, these animals tended to reduce T 4 hormone concentrations to reduce heat production (Table 2), probably due to the difficulty in dissipating heat through evaporative skin thermolysis (Maia et al , 2009). Bertipaglia et al (2008) found a relationship between coat traits and reproductive indices, in which the animals that had short HL showed shorter calving intervals.…”

“…The physical structure of the hair coat is the first layer of defence protecting animals from direct sunlight. This protection differs according to many factors such as coat thickness (CT) and hair characteristics (Silva 2008;Maia et al 2009). Substantial research has been conducted to analyse the relationship between coat characteristics and livestock productivity and other traits that are not directly related to thermoregulation (Bertipaglia et al 2007(Bertipaglia et al , 2008.…”

Genetic assessment of rectal temperature and coat score in Brahman, Angus, and Romosinuano crossbred and straightbred cows and calves under subtropical summer conditions

“…This has not been experimentally confirmed in this herd. There may be some influence of coat color on coat condition or amount of hair (Finch, 1984;Maia et al, 2009;Landaeta-Herná ndez et al, 2011).…”

“…Estimates of heritability for hair weight and length in Angus cattle were 0.21 and 0.09, respectively (Morris et al, 2011). Maia et al (2009) reported an estimate of heritability for the effective thermal conductivity of the coat as 0.18. Slick-coated cattle had lower rectal temperatures (Alava, 2009;Olson et al, 2003); that was the case as well in the present study if the Romosinuano and some crosses were considered as having slick coats (though not attempting to formally classify certain coat scores as slick).…”