Dairy cattle in the tropics are exposed to chronic heat stress, which have an effect on the cow’s ability to maintain body temperature at normal levels. The objective of this experiment was to evaluate rectal temperatures (RT), heart rates (HR), and respiration rates (RR) in lactating Holstein cows with 2 hair genotypes, slick-hair (SL) and wild-type (WT). An allelic discrimination assay was used to determine the presence or absence of the SL gene mutation. Slick-hair (n = 8; BW 595.1 kg ± 5.9; DIM 135.4 ± 28.5; milk yield 20.5 kg ± 0.9) and WT (n = 8; BW 563.1 kg ± 4.9; DIM 145 ± 28.4; milk yield 19.5 kg ± 0.9) Holstein cows were used in this experiment that lasted 60 d. Animals were fed ad libitum a TMR based on Brachiaria spp. forage, soybean meal, steam flaked corn grain, brewers’ grains, and minerals. The average ambient temperature during the study was 25.7°C ± 0.03, while the average ambient humidity was 78.5% ± 0.24, resulting in an average temperature-humidity index (THI) of 75.8 ± 0.03. Weekly RT, RR, and HR were determined at 0600 and 1800h. A digital thermometer was used to determine RT. A stethoscope was used to determine HR, while RR was determined by means of visual observation of the flank for 1 min. Weekly averages of RT, RR, and HR were analyzed using Proc Mixed of SAS (SAS University Edition, 2018) using a model that included genotype (SL and WT), week and their interactions as fixed effects. For each parameter, week was used as a repeated measurement, with cow as the subject. There was no interaction between genotype and week in terms of RT, RR, and HR (P ≥ 0.29). While SL had an average RT of 38.4°C ± 0.08; WT showed a higher RT of 38.7°C ± 0.08 (P < 0.0001). Likewise, while SL had an average RR of 43 ± 1.08 respirations per minute, WT had a higher average RR of 59 ± 1.18 respirations per minute (P < 0.0001). Moreover, whereas SL had an average HR of 70 ± 0.13; WT showed a higher HR of 73 ± 1.14 (P < 0.05). Overall, under the conditions of this experiment, SL and WT dairy cows seem to experience and cope with heat stress in a dissimilar manner. Slick-hair cows seem to be better adapted to conditions of heat stress.