I. ALEXIEV1, D. GUDEV1, S. RALCHEVA1, P. MONEVA1 and P. ZUNEV2
1 Institute of Animal Science, BG - 2230 Kostinbrod, Bulgaria
2 Institute of Mountainous Animal Breeding and Aagriculture, BG - 5600 Troyan, Bulgaria
ALEXIEV, I., D. GUDEV, S. RALCHEVA, P. MONEVA and P. ZUNEV, 2004. Thermoregulation in kids. Diurnal dynamics of rectal temperature, respiration rate and heart rate in Bulgarian white kids kept in sun or in shade. Bulg. J. Agric. Sci., 10: 499-505
Five-six month old kids (Bulgarian white goat), kept in sun or in shade, was used to study the effect of high ambient temperature on the dynamics of rectal temperature (RT), respiration rate (RR) and heart rate (HR).
The animals in shade were housed either in solid barn with half opened front side or kept in canvas shade. All measurements were carried out when the ambient temperature was more than 30°C with the exception of the animals housed in the barn, where, the measurements were made at two levels of the ambient temperature: under 30°C (BU) and above 30°C (BA). The physiological parameters were registered from 7 a.m. to 9 p.m. at intervals of two hours. The meteorological parameters were controlled at the same hours.
Exposure to direct solar radiation resulted in rapid increase of both rectal temperature and RR. Heat flux to the kids exposed to direct solar radiation was highest at 1 p.m. Their RT and RR did not follow the further rise in the ambient temperature, which peaked at 3 p.m.
The equal RT of the lambs in sun (at 1 p.m.) and in shade (BA at 9 p.m.) was accompanied by three times higher respiratory rate in the exposed to sun kids. This phenomenon was attributed to the diurnal neuroendocrine dynamics and especially to the rising levels of melatonin during late afternoon hours when melatonin could signal the brain for the forthcoming cooling during the night.
When kids were transferred into a canvas shade for 30 min. following continued exposure to solar radiation (7 a.m. - 12 a.m.) RT and RR declined quickly. The kids kept in canvas shade showed the lowermost strain of the thermoregulatory mechanism. Heat load values were 8.08; 3.14; 2.47 and 2.31 for the kids kept in sun or shade (BA, canvas shade, BU), respectively.