Hérica Girlane Tertulino Domingos

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

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.

Retraction Note: Regional differences in the surface temperature of naked neck laying hens in a semi-arid environment

The aim of this study was to evaluate the regional differences in the surface temperature of Naked Neck hens that were subjected to different temperatures in a semi-arid environment. The surface temperature was measured in four body regions (face, neck, legs and feathered area) of 60 Naked Neck hens. The following environmental variables were measured at the center of the shed: the black globe temperature (T G ), air temperature (T A ), wind speed (U) and relative humidity (R H ). The T A was divided into three classes: 1 (24.0–26.0 °C), 2 (26.1–28.9 °C) and 3 (29.0–31.0 °C). An analysis of variance was performed by the least squares method and a comparison of the means by the Tukey-Kramer test. The results showed a significant effect of T A class, the body region and the interaction between these two effects on the surface temperature. There was no significant difference between the T A classes for the face and neck. The legs and feathered area showed significant differences between the T A classes. Regarding the effect of body regions within each T A class, there was a significant difference among all regions in the three T A classes. In all T A classes the neck had the highest average followed by the face and legs. The feathered area showed the lowest average of the different T A classes. In conclusion, this study showed that there are regional differences in the surface temperature of Naked Neck hens, with the legs acting as thermal windows.

Temperatura da Superfície Corporal e Fluxo de Calor Convectivo em Vacas Holandesas Expostas à Radiação Solar Direta no Semi-Árido

O objetivo deste trabalho foi determinar a variacao diaria da temperatura da superficie do pelame e as trocas termicas por conveccao em vacas Holandesas expostas a radiacao solar direta em funcao das condicoes meteorologicas do dia no Semi-Arido. O pico da temperatura da superficie do pelame coincidiu com o valor maximo da temperatura do ar que ocorreu as 12:00 h com 44,0 oC e teve seu minimo as 18:00 h com 33,1 oC. Os horarios em que a dissipacao de calor por conveccao foi mais elevada ocorreu nos periodos entre 8:00 h e 11:00 h e 14:00 as 15:00 h, tendo seus valores maximos as 10:00 h com 68,3 W.m-2, com temperatura do ar de 31,7 oC e temperatura do pelame de 43,1 oC, e as 14:00 h com 61,3 W.m-2 tendo valores de temperatura do ar e da superficie do pelame de 31,9 oC e 41,7 oC respectivamente. O valor minimo para a perda de calor por conveccao ocorreu as 18:00 h com 30 W.m-2 com valores de 28,6 oC e 33,1 oC para temperatura do ar e temperatura do pelame respectivamente. Com isso, para manter-se na zona de termoneutralidade, os animais precisarao ativar os mecanismos latentes de dissipacao de calor. DOI: 10.15528/2176-4158/rcpa.v12n1p6-9