INFLUENCE LF WATER TEMPERATURE AND HEAT STRESS LN DRINKING WATER INTAKE IN DAIRY CLWS

Grazing animals are exposed to heat stress and there should be conditions to facilitate water intake. Three experiments were carried out to determine the relationship between water intake, water temperature, and heat stress for Holstein pastured dairy cows. Experiment 1: Drinking behavior of 13 cows was evaluated (for 3 consecutive days) and four time periods were established according to the temperature humidity index (THI): (H1:05:00 to 10:59 h, H2:11:00 to 16:59 h, H3:17:00 to 22:59 h, and H4:23:00 to 04:59 h). The highest mean percentage of drinking bouts (53.2%) was registered in H2 (THI: 74.91 to 83.95). Drinking bout means among time periods were different (p < 0.05), thus showing that heat stress conditions influence drinking behavior. Experiment 2: Three water troughs were placed in the sun (S) and three under a 2.2 m high structure covered with shade cloth (MS). Water temperature was registered at 10:00, 13:30, and 17:00 h, twice a week for 6 weeks. Mean water temperatures at 17:00 h were 33.2 ± 1.6 °C (S) and 25.3 ± 1.9 °C (MS) and showed significant differences (p < 0.05), thus supporting the shade cloth effect. Experiment 3: Five cows were offered water simultaneously at 18 and 31 °C (T1 and T2), for 10 min, twice a day for 5 d. There were no significant differences among treatments (p > 0.05). Recorded water intake in T1 (18 L) was lower than in T2 (35.9 L), although body heat dissipation was higher (T1 = 672.64 kJ d-1, T2 = 620.76 kJ d-1).