Evaporative Heat Losses in Different Coloured Brazilian Hair Sheep

In the year 2030, it is estimated that the planet is probably 1°C - 2°C warmer than today and these changes can have a significant impact on livestock production and on food supply to human population. Thermal comfort of animals in tropical regions depends largely on their ability to dissipate excess body heat by evaporative cooling, being skin surface evaporation the main way for heat dissipation. Heat stress is one of the most important factors that affect sheep production in tropical regions. The searching of locally adapted genotypes is increasing in the last years, in brazilian semiarid regions, with the aim to develop efficient livestock systems in these areas. The Morada Nova hair sheep is a native breed of Northeastern of Brazil, adapted to the high levels of solar radiation that occurs during all seasons. There are two official varieties, the Red Colored and the White Colored animals, both reared under extensive system conditions, exposed to high temperatures during the wet and the dry seasons. These animals are generally able to maintain satisfactory indexes of reproductive traits, as high fertility and maternal ability, compatible with a high meat production. The red variety have maintained its census, however, white colored animals have been reducing the female amount over the last year, and now it became a threatened genetic resource.

The goal of this study was to evaluate the evaporative heat losses in Red and White varieties of Morada Nova hair sheep, in a semiarid region, during the rainy season.

The study was performed during the wet season in a semiarid region of Brazil, located at 5,4°S. The data were collected during two months in 40 white colored ewes and 80 red colored Morada Nova ewes from commercial herds. Rectal temperature (RT, °C), respiratory rate (RR, breath for minute) and skin surface temperature (ST; °C) were collected in each animal once a day. The cutaneous evaporative thermolysis (CE; W/m²) of two body regions (neck and flank) was estimated with a ventilated capsule, at the same time of the other thermoregulatory traits. The device was fixed on body surface in order to obtain the amount of evaporated water. This variable was calculated using the following function: CE = X/AT, where CE is the cutaneous evaporation (W/m²); X is the water lost by sweating (g);  is the latent heat of vaporization of water (J/g); A is the contact area of the capsule (m2) and T is the time of contact between the capsule and the body surface. At the time of sample, around 11am and 2pm the animals were exposed to the sun. The environmental traits registered consisted in wind speed (WS, m/s), air temperature (AT, °C), wet bulb temperature (WBT,°C) and black globe temperature by sun (BGT, °C), utilized to estimate the radiant heat load (RHL, W/m²). The data were initially analyzed by the last-squares method, the model consider the effect the coat color (white and red), sampling day, the CE in body region (neck and flank). To test our hypothesis, a distance-based permutational-repeated measures MANOVA was fitted, with variety and sampling day as fixed factors and RR, RT, ST and neck and flank CE as variables. The interactions between variety (coat color) and sampling day were investigated using posteriori pairwise comparisons with PERMANOVA t statistic. Variables more affected by factors (variety and sampling day) were determined using Canonical analysis of principal coordinates (CAP) and Spearman correlation between variables and principal coordinates. The environmental variables as RHL and RH, were used as covariate in order to correct the MANOVA model and ensure that there were differences between varieties regardless of these environmental variables. All statistical analysis were carried out by PERMANOVA + (PRIMER-E Ltd., Plymouth, UK).

We did not detect differences in Radiant Heat Load (RHL) between white (Mean RHL = 653.77 W/m2) and red (Mean RHL = 650.12 W/m2) varieties environment. However, significant differences were found in environmental relative humidity where red (RH = 89.0%) and white (78.0%) colored ewes were located.

The variance analyze showed that the effects of body region (neck and flank) were no significant to heat loss. The white variety showed significantly higher values (312.42 w/m²) of CE than red animals (255.96 w/m²). However, surface temperature was significantly higher in red variety (40.67°C) than in white variety (37.40°C). In both variety the rectal temperature were not differences. There are differences between red and white coat color reflectance and absorptance, in this study the exposure of the goats to sun caused the animals to gain an excess thermal energy and an increase of the coat surface temperature.

In both sampling, the white ewes exhibited higher CE and lower RR and body ST, while the red colored ewes tend utilized more efficiently respiratory thermolysis. It is possible that the red animals presented a higher ST and, therefore they activated the respiratory losses to reach homeothermic conditions, then the need of sweating was lower. Light coats above pigmented skin have been considered most desirable ones for livestock in tropical areas as dark coated animals tend to acquire greater heat from solar radiation, in this experiment each varieties showed different way to reach homeostasys.

The white Morada Nova variety have a similar adaptive capacity when compared to the red Morada Nova so it can be included in breeding programs as a superior locally adapted genotype to meat production in semiarid regions.

We conclude that White Morada Nova used CE as a main way of heat loss and maintain homeothermic conditions; however, Red Morada Nova tend used RR as the main way to ensure homeothermic conditions.