Anual variation of morphologic traits and hair coat surface temperature of Holstein cows in semi-arid environment

Abstract

RESUMO -O objetivo neste trabalho foi estudar a variação anual da temperatura superficial e outras características do pelame de vacas holandesas em ambiente tropical, considerando separadamente as malhas negras e brancas. Foram medidas as características espessura da capa (mm), comprimento dos pelos (mm), número de pelos (pelos/cm 2 ) e temperatura da superfície do pelame em 191 vacas mestiças com alta proporção de sangue holandês (7/8 e 31/32, respectivamente), distribuídas em três rebanhos em ambiente semiárido. O pelame menos denso, com pelos mais curtos e assentados, que ocorreu predominantemente no mês de março, coincidiu com altos níveis de radiação solar. Esse tipo de pelame apresenta menor resistência ao fluxo de calor latente e sensível através da capa, favorecendo a termólise. A temperatura da superfície do pelame preto foi em média 4ºC maior que a do pelame branco ao longo do ano e essa variação acompanhou a da temperatura radiante média. Os modelos desenvolvidos para predizer a condutividade térmica efetiva do pelame devem considerar essas diferenças, pois, no caso de animais Holandeses malhados de preto e branco, manejados em ambiente tropical, o gradiente de temperatura no sentido horizontal não é negligível, assim como as características da capa também não o são.Palavras-chave: adaptação, ambiente tropical, bovinos leiteiros, capa externa Anual variation of morphologic traits and hair coat surface temperature of Holstein cows in semi-arid environmentABSTRACT -This work aimed to study the annual variation of temperature of the coat surface and other traits of coat in Holstein cows managed in a tropical environment by separately considering black coat and white coat. It was measured the coat thickness (mm) characteristic, hair length (mm), hair number (hair/cm 2 ) and coat surface temperature on 191 crossbred cows with 7/8 and 31/32 Holstein composition distributed in 3 herds in a semi-arid environment. Less dense coats with shorter, flattened hair occurred predominantly in March, a time coinciding to high levels of solar radiation. This type of coat shows low resistance to the flux of latent and sensitive heat through the skin, thus favoring heat loss. The black coat surface temperature was on average 4ºC higher than that of the white one during all the year and its variation followed that of the mean radiant temperature. The models developed to predict the effective thermal conductivity of the coat must take these differences into account because the thermal gradient parallel to the skin surface is not negligible for Holstein cows under the sun in a tropical environment, as well as the other traits.

Physiological parameters, hair coat morphological characteristics and temperature gradients in holstein-gyr crossbred cows

“…The recorded values were similar to those reported in Holstein cows in winter (2.88 mm; Mata and Silva et al, 2013) and higher than those recorded in crossbred dairy cows in a semiarid region (1.93 mm; Façanha et al, 2010). These authors reported higher hair coat thickness values in animals harboring high proportions of Holstein genes than in animals derived from crossbreeding with Guzera cows, which are more adapted to tropical environments and, thus, exhibit a thinner coat with short, wellsettled hairs, which contributes to a greater loss of heat energy.…”

Thermoregulatory, behavioral, and production traits of ½ and ¾ Holstein/Gir dairy cows

“…This variable is prone to variations, since it is associated with the environment, climatic changes, and physiological changes such as vascularization and perspiration (FERREIRA et al, 2006). Façanha et al (2010) submit that the hair-coat color influences the body temperature due to the greater heat absorption. In the present study, all animals had a black epidermis.…”

Shade Modifies Behavioral and Physiological Responses of Low to Medium Production Dairy Cows at Pasture in an Integrated Crop-Livestock-Forest System

“…Several coat characteristics are preferable for cows in tropical climates, such as short, high-density coats, high diameter, and light-colored hair with an inclination less than 40 • , and pigmented skin [38,39]. These characteristics allow more protection from solar radiation and heat stress, contributing to animal comfort and better production under field conditions [40].…”