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

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/cm²) 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.

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

Revista Brasileira de Zootecnia ◽

10.1590/s1516-35982009001100022 ◽

2009 ◽

Vol 38 (11) ◽

pp. 2218-2223 ◽

Cited By ~ 11

Author(s):

Alex Sandro Campos Maia ◽

Roberto Gomes da Silva ◽

João Batista Freire de Souza Junior ◽

Rosiane Batista da Silva ◽

Hérica Girlane Tertulino Domingos

Keyword(s):

Heat Transfer ◽

Thermal Conductivity ◽

Free Convection ◽

Effective Thermal Conductivity ◽

Tropical Environment ◽

Holstein Cows ◽

Hair Coat ◽

Black And White ◽

Low K

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.

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Nitrogen fertilizer and wheat in a semi-arid environment. 1. Effect on yield

Australian Journal of Experimental Agriculture ◽

10.1071/ea9670453 ◽

1967 ◽

Vol 7 (28) ◽

pp. 453 ◽

Cited By ~ 10

Author(s):

JS Russell

Keyword(s):

Nitrogen Fertilizer ◽

South Australia ◽

Arid Environment ◽

Yield Response ◽

Considerable Variability ◽

Mean Values ◽

Comparable Level ◽

The Mean ◽

Effect On Yield ◽

Semi Arid

Response experiments with Gabo wheat at four rates of ammonium sulphate (0, 11.5, 23, and 46 lb N an acre) were carried out at a number of widely-spread locations in the cereal growing areas of South Australia during six seasons in the period 1956-61. Considerable variability in grain and grain + straw yield and in the observed response to nitrogen fertilizer was found. Season and site effects were marked and season-site interactions were also observed. The mean grain yield response was 8.7, 7.2, and 5.1 lb grain for each lb of nitrogen applied as fertilizer at the rates of 11.5, 23, and 46 lb N an acre. These mean values are lower than those reported for other more humid wheat growing areas, but there are conditions where response is at a comparable level. The main difficulty lies in predicting these situations. Several aspects of the use of nitrogen fertilizer in a semi-arid environment are discussed.

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