SEASONAL VARIATIONS OF THE PLASMA THYROID HORMONE CONCENTRATIONS AND THE BODY TEMPERATURE IN THE DROMEDARY CAMEL

摘要

The study of the season effect on the plasma thyroxin (T_4) and triiodothyronin (T_3) concentrations in camel was performed on 5 castrated male camels, 6 to 8 years old. The herd was bred according to the nomadic system in Guelmim (desert area in thesouthern Morocco) where the ambient temperature ranged from 6 to 20°C during the humid season (November - April) and from 19 to 40°C during the dry season (May - October). Blood samples were collected every 45 days over the year at early morning beforegoing to the pasture. The mean body temperature varied from 36.7 ± 0.2 to 37.1 ± 0.2°C in the morning and from 38.0 ± 0.2 and 38.7 ± 0.2°C in the evening. The mean plasma T_3 and T_4 concentration ranged from 78.0 ± 2.7 ng/100 ml to 94.0 ± 5.4 ng/100 ml and from 10.3 ± 0.18 ug/100 ml to 11.3 ± 0.26 ug/100 ml, respectively. There was a significant correlation between the plasma T_3 and T_4 concentrations (r = 0,82 ; p < 0,01). The season has a significant effect (p < 0.05) on the plasma T_3 and T_4 concentrations with high levels during winter and low levels during summer. Negative correlation was observed between the temperature gap and the plasma T_3 (r = -0.34 ; p< 0.05) and T_4 (r=-0.42 ; p < 0.05). This effect is related to" a combined effect of seasonal variation of the feed supply, the ambient temperature and photoperiod; however, the part of each factor could not be established.