Estratégias de manejo ambiental e termorregulação de cabritos neonatos em ambiente tropical.

Abstract

Newborn goat kids can face temperature challenges ranging from cold to heat in tropical regions, either during the day, at highest temperatures or at night, when the lowest temperatures are recorded. The radiant temperature and abundant wind can facilitate or impair the amount of sensible heat loss to the environment, being necessary to make adjustments in the animal's shelter environment, using an additional source of radiation or shading source. We evaluated newborn goat kids in the first 72 hours of life to see if they would voluntarily access the supplementary heat source and shading area available in the experimental pen and the impact on their body temperature. The goat kids used (n = 16) were obtained from calving of nine goats (Alpine x Saanen) in a pen that had a private source of supplemental heat (135x200x130 cm, length, width, height) provided a light bulb. (power = 250 W), a shaded area (528x246 cm) and an unshaded area (880x610 cm). The mean radiant temperatures in the supplementary environment heat source (TRM, ºC) and the open environment (TRM, ºC) were recorded. Different behavioral variables of the goat kids were evaluated in the first hours afterbirth: location (if exposed to the shade, the sun, or directly under the heat source) and distance from the mother (if near or far). The time spent by newborn goat kids under the supplementary heat source environment, in the shaded area, and in the area without shading were quantified during 72 hours through direct observation, focal animal sampling, and instantaneous recording at every 10 min interval. Also, the (TS, ºC) and rectal (TR, ºC) temperatures were recorded hourly. Generalized linear models were used to test the effects of the time of day (i) and the thermal environment conditions (j) on the independent variables. The newborn goat kids experienced higher TRM in the supplemental heat source environment (range = 30 to 32 ºC) than in the open environment (range = 18 to 23 ºC), which may explain their preference (P < 0.05) to remain in the environment with supplemental heat source during the night, spending in average, 70% of the time in this environment, regardless of whether they are close to or far from their mother. In the period from 07:00 to 17:00 h, the kids spent most of their time under the shade, ranging from 75 to 97%, showing that when there is an increase in solar radiation, the animals use the available shade to avoid direct radiation. When newborn goat kids were in the extra heat source environment, they benefited from a smaller thermal gradient between their surface temperature and mean radiant temperature (TS = 30 °C vs TRM supplementary heat source = 32 ºC), than in the open environment (average TS = 28 ºC vs average TRM = 20 ºC). When exposed to solar radiation, the TR ranged from 37.8 to 39.7 °C, and the TS ranged from 24.0 to 38.2 °C. In the shaded area, the TR ranged from 38.7 to 39.2 °C, and the TS ranged from 28.0 to 33 °C. Regardless of the thermal conditions, the rectal body temperature of newborn goat kids was kept in a narrow range of variation (38.4 to 38.9 ºC). We could conclude that newborn goat kids raised in tropical conditions voluntarily access the supplementary heat source and shaded area during the night and day, which allows them to perform the thermal balance efficiently, preventing hypothermia in the cold and hyperthermia in the heat temperatures. Newborn goat kids seem to demonstrate certain early independence from their mothers, classified as early thermoregulators. Managing the microclimate where newborn goats are kept, whether in avoiding cold stress by providing a supplementary heat source or avoiding heat stress by providing shade, is decisive for the quality of life and animal welfare, reflecting on the efficiency of the production system.