Coat and skin morphology of hair sheep breeds in an equatorial semi-arid environment.

This study aims to address if are there annual changes in the hair coat traits and skin morphology of hair sheep breeds raised in an equatorial semi-arid region? Coat and skin samples were taken from thirty Morada Nova (4 ±â€¯2 years old; red coat; ±SD) and twenty Santa Inês multiparous ewes (5 ±â€¯2 years old; brown and black coat; ±SD) every 3 months over a year. Hair coat traits included thickness (mm), density (number of hairs cm-2), length (mm), and diameter (mm), plus epidermal and dermal thickness (µm), sweat glands and blood capillaries area (µm cm-2) were determined. Means of solar irradiance and ambient air temperature were higher between September and December. Annual changes (P < 0.05) in hair density, diameter, length and thickness, as well as the skin blood capillaries and sweat gland area differed between breeds. The modifications on hair coat traits resulted in minor changes on the effective thermal conductivity of the hair coat surface both for Morada Nova and Santa Ines sheep. Nevertheless, it was clearly evident that the overall cutaneous thermal insulation for Morada Nova sheep was lowest in September that was coupled with lower hair density, coat thickness, and higher sweat gland and blood capillary area (P < 0.05). In conclusion, even in an equatorial region, phenotypic acclimatization on morphological traits of cutaneous surface and skin traits can modify the overall thermal insulation of sheep breeds.

The use of simple physiological and environmental measures to estimate the latent heat transfer in crossbred Holstein cows.

The aim of the present study was to estimate the heat transfer through cutaneous and respiratory evaporation of dairy cows raised in tropical ambient conditions using simple environmental and physiological measures. Twenty-six lactating crossbred cows (7/8 Holstein-Gir) were used, 8 predominantly white and 18 predominantly black. The environmental variables air temperature, relative humidity, black globe temperature, and wind speed were measured. Respiratory rate and coat surface temperature were measured at 0700, 0900, 1100, 1300, and 1500 h. The environmental and physiological data were used to estimate heat loss by respiratory (ER) and cutaneous evaporation (EC). Results showed that there was variation (P < 0.01) for respiratory rate depending on the times of the day. The highest values were recorded at 1100, 1300, and 1500 h, corresponding to 66.85 ± 10.20, 66.98 ± 7.80, and 65.65 ± 6.50 breaths/min, respectively. Thus, the amount of heat transferred via respiration ranged from 19.21 to 29.42 W/m2. There was a variation from 31.6 to 38.8 °C for coat surface temperature; these values reflected a range of 55.52 to 566.83 W/m2 for heat transfer via cutaneous evaporation. However, throughout the day, the dissipation of thermal energy through the coat surface accounted for 87.9 % total loss of latent heat, and the remainder (12.1 %) was via the respiratory tract. In conclusion, the predictive models based on respiratory rate and coat surface temperature may be used to estimate the latent heat loss in dairy cows kept confined in tropical ambient conditions.

Models to predict both sensible and latent heat transfer in the respiratory tract of Morada Nova sheep under semiarid tropical environment.

The aim of this study was to build a prediction model both sensible and latent heat transfer by respiratory tract for Morada Nova sheep under field conditions in a semiarid tropical environment, using easily measured physiological and environmental parameters. Twelve dry Morada Nova ewes with an average of 3 ± 1.2 years old and average body weight of 32.76 ± 3.72 kg were used in a Latin square design 12 × 12 (12 days of records and 12 schedules). Tidal volume, respiratory rate, expired air temperature, and partial vapor pressure of the expired air were obtained from the respiratory facial mask and using a physiological measurement system. Ewes were evaluated from 0700 to 1900 h in each day under shade. A simple nonlinear model to estimate tidal volume as a function of respiratory rate was developed. Equation to estimate the expired air temperature was built, and the ambient air temperature was the best predictor together with relative humidity and ambient vapor pressure. In naturalized Morada Nova sheep, respiratory convection seems to be a mechanism of heat transfer of minor importance even under mild air temperature. Evaporation from the respiratory system increased together with ambient air temperature. At ambient air temperature, up to 35 °C respiratory evaporation accounted 90 % of the total heat lost by respiratory system, on average. Models presented here allow to estimate the heat flow from the respiratory tract for Morada Nova sheep bred in tropical region, using easily measured physiological and environmental traits as respiratory rate, ambient air temperature, and relative humidity.