Current assay evaluates thermoregulatory characteristics of native sheep in pregnancy and supplemented in grazing system. Were used 24 multiparous lactating ewes, 12 Santa Inês and 12 Morada Nova, with an average weight of 52.6 and 31.3 kg, respectively, were randomly distributed in a completely randomized split-split plot design. Physiological parameters such as heart rate (HR), respiratory rate (RR) and rectal temperature (RT) were measured in that order during the morning and afternoon, 06-07 and 13-14 h, respectively, every seven days, totaling 10 samples. The environmental temperature was higher (P<0.05) in the afternoon, probably due to the higher incidence and intensity of sunlight at this time, with index globe temperature and humidity presenting values that characterize an environment of danger to animal production, characteristics of the semiarid. Effect (P<0.05) turn and race on the thermoregulatory characteristics of the sheep were found, showing unfavorable conditions in the afternoon with greater intensity of use of heat dissipation mechanisms by Santa Inês ewes. Assessing the effect of supplementation on the physiology of these sheep, it appears that there is an influence (P<0.05) on the RR and HR, with higher values for Santa Inês ewes subjected to 1.5% concentrate diet. However, RT remained within the normal range, indicating that they are adapted breeds rearing conditions and experimental diet that have efficient mechanisms in respiratory heat dissipation, indicating also that they are qualified to productive farm animals in semi-arid conditions.