Effect of birth season on Holstein calves’ voluntary water intake

Usually dairy calves do not have access to fresh water in the first d of life, even in summer when heat load is highly severe in certain challenging climatic areas. Although heat stress mitigation strategies, such as fans and sprinklers, are commonly present in the lactating cows’ barn, in Italy newborn dairy calves are generally kept outdoor, and exposed to high temperature-humidity index (THI) in summer. In this study, we evaluated how the maximum THI (maxTHI) to which animals were exposed from 11 a.m. to 5 p.m. affected voluntary water intake in the first 21 d of life (WI). We recorded daily WI in randomly selected female Holstein calves on an Italian commercial farm located in Po River Valley: 21 born in spring (mid-April to mid-June) and 22 in summer (late June to late August). Data were collected by the same operator and all calves were separated from the mother immediately after calving, provided with 6 L of colostrum in the first 6 h of life, kept in individual igloo pens, and fed twice a day with the same protocol and amount of milk replacer. In the 2 seasons average temperature between 11 am and 5 pm was 23.6 and 31.3°C, respectively, with maxTHI averaging 70.3 and 81.3. Regardless of season, by the first week of life, 20% of calves voluntarily drank some water. A one-way ANOVA was carried out with PROC GLM of SAS software v.9.4 for average daily WI and cumulative WI considering season as fixed effect. The effect was significant for both average (0.98 vs. 1.92 L, P < 0.01) and cumulative WI (16.45 vs. 26.77 L, P < 0.01). Although specific ethological data were not recorded, we systematically observed that buckets stimulated calves’ curiosity and play behavior, e.g., blowing bubbles. Given that WI was non-negligible, even in spring, offering water to calves (an often overlooked practice) seems a low-cost, meaningful and positive measure for health and welfare, particularly in contexts with no early-life heat mitigation. Further research should be based on larger dataset, covering winter season and ethological aspects too. Investigating the effect of heat stress on number and length of daily bouts is advisable to calculate water requirement.