Identifying potential thermal drivers of sudomotor in camels (Camelus dromedarius)

The mechanism of sudomotor regulation in the family Camelidae, as in other mammals, is poorly understood. Five healthy dromedary bulls (400 kg and 4 years-old) were used to examine the interrelationship of sweating rate (SR) with ten thermal parameters measured (and/or estimated) every 3-hr for a 24-hr time period under natural and shaded environmental conditions, in order to subsequently identify the potential thermal drivers of sudomotor in this species. Results revealed that all parameters, including SR, had clearly (P < 0·001) exhibited monophasic circadian rhythms. Moreover, the obtained findings pointed out that strong/moderate positive correlations were existed between SR and eight parameters [i.e. ambient (Tₐ), rectal (Tᵣ), body (Tb), skin (Tₛₖ), coat (Tcₜ) temperatures as well as total (ambient-to-body, BTGₜ), external (ambient-to-skin, BTGₑₓ), and internal (skin-to-body, BTGᵢₙ) body thermal gradients] suggesting that they may all be good indicators of sweating activity. Nonetheless, out of those highly-correlated parameters, merely six (i.e. Tₐ, Tb, Tₛₖ, Tcₜ, BTGₜ, and BTGₑₓ) showed superior coefficients of determination (R² ≥ 0·90; P < 0·000) when interrelated with SR; thereby, implying that they have the potential to drive sudomotor. Notably, however, results were more probably allude that sudomotor is regulated through BTGₜ. Accordingly, the onset of sweating (i.e. threshold) and its effective level was determined using BTGₜ. A method of how SR can be regulated through BTGₜ was proposed according to Webb’s theory of controlling body-heat content. Some shortcomings prevent confirming that BTGₜ is the best thermal driver of sudomotor in this species were noted. Research dealing with this interesting physiological process requires further experimentation to fully elucidate the basic functional mechanisms of Camelidae's thermoregulatory system .