Abstract
The aim of the study was to evaluate the influence of heat stress (high ambient temperature) on physiological parameters, body surface temperature, thyroid hormones (triiodothyronine=T-3 and tetraiodothyronine=T-4) and testosterone levels in llamas in relation to the body fibre. Therefore 12 fertile male llamas were housed in heated stables during the study. 5 of the animals were shorn (< 1 cm), 5 animals were left unshorn and 2 animals were shorn partly (barrel cut). After a short period of acclimatization, the ambient temperature was elevated up to 30 degrees C for a period of 4 weeks. Afterwards the temperature was decreased over one week to 20 degrees C. The animals were kept for at least 7 weeks this temperature. Rectal temperature, heart rate and respiratory rate were measured daily. In addition the body surface temperature was measured by infrared thermography. Blood samples were taken to estimate serum thyroid hormone and serum testosterone levels once a week. All animals showed higher respiratory rates (p < 0.001) and rectal temperatures in the heat-period when compared with the recovery-period. Respiratory rates were above the physiological values during the heat period. The rectal temperature stayed within the physiological range. Shorn animals were able to cope better with the high ambient temperature and showed significantly lower rectal temperatures and respiratory rates during the heat-period when compared with the other animals. The body surface temperature was significantly lower in the unshorn regions of the animals when compared with the shorn parts. The heat loss in the unshorn animals was concentrated on the ventral body regions (the thermal windows), which shows that effective thermoregulation can only take place in this part of the body. In the heat-period the thyroid hormone levels (T-3 and T-4) were both significantly lower (p < 0.001, p < 0.01) when compared with the recovery-period. The two thyroid hormone levels were significantly correlated. The serum testosterone level showed a decrease one week after the heat-period, with a minimum level 2 weeks later, followed by a slow increase with the levels still below the initial values until 6 weeks after the heat-period. There were no significant differences in the testosterone levels between shorn and non shorn animals. The high ambient temperature showed significant effects on the measured physiological parameters and the thyroid hormone levels in all llamas. In unshorn animals an effective thermoregulation can only take place over the thermal windows. Shorn animals seems to tolerate heat better because of the heat loss over the hole of the body surface.