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Influence of water temperature and heat stress on drinking water intake in dairy cows Pereyra, Ana Valeria González; May, Verónica Maldonado; Catracchia, Carlos Guillermo; Herrero, María Alejandra; Flores, Myriam Celina & Mazzini, Mariana Abstract 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 (TI-11): (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 ± 1.6ºC (S) and 25.3 ± 1.9ºC (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 ºC (Tl 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 Tl (18 L) was lower than in T2 (35.9 L), although body heat dissipation was higher (Tl = 672.64 kJ d -1 , T2 = 620.76 kJ d -1 ). Keywords drinking behavior, summer time, THI, grazing dairy farms

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Influencia de la temperatura del agua y el estrés calórico sobre el consumo de agua de bebida en vacas lecheras Pereyra, Ana Valeria González; May, Verónica Maldonado; Catracchia, Carlos Guillermo; Herrero, María Alejandra; Flores, Myriam Celina & Mazzini, Mariana Resumen Los animales en pastoreo están expuestos al estrés calórico, siendo fundamental proveer agua en condiciones que faciliten su consumo. Se desarrollaron tres experimentos para determinar las relaciones entre el consumo del agua de bebida con la temperatura del agua y el estrés calórico, en vacas lecheras en pastoreo. Experimento 1: Se evaluó el comportamiento de abrevado en 13 vacas (3 días consecutivos), estableciéndose cuatro franjas horarias según índice de temperatura y humedad (THI): (H1:05:00-10:59 h, H2:11:00-16:59 h, H3:17:00- 22:59 h y H4:23:00-04:59 h). En H2 (THI: 74,91-83,95) se registró el mayor porcentaje medio de accesos al bebedero (53,2%). Las medianas de los eventos “beber” por franjas horarias resultaron diferentes (p < 0,05), demostrándose que las condiciones de estrés calórico influyen sobre el comportamiento de bebida. Experimento 2: Tres bebederos con agua fueron colocados al sol (S) y tres bajo estructura de red 80% sombra (MS), a 2,2 m de altura, registrándose la temperatura del agua a las 10:00, 13:30 y 17:00 h, dos veces por semana (6 semanas). A las 17:00 h la temperatura media del agua, 33,2 ± 1,6 ºC (S) y 25,3 ± 1,9 ºC (MS) presentó diferencias significativas (p < 0,05), mostrando el efecto de MS. Experimento 3: Se ofreció agua a 18 y 31 ºC (T1 y T2) durante 10 min dos veces al día (5 d) a cinco vacas. No hubo diferencias significativas entre las proporciones de respuesta a los tratamientos (p > 0,05). Se registró menor consumo con T1 (18 L) respecto a T2 (35,9 L), pero mayor disipación de calor corporal (T1 = 672,64 kJ d-1 , T2 = 620,76 kJ d-1 ). Palabras-clave comportamiento de abrevado, época estival, ITH, granjas lecheras pastoriles

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