Effects of salt (NaCl) drinking water on physiological and productivity responses of dairy cattle.

Climate change is increasing the risk of freshwater scarcity in dairy production, highlighting the need to evaluate alternative water sources. This study investigated the physiological and production responses of dairy cows offered drinking water with salinity comparable to that of the brackish Baltic Sea (salinity 0.2 - 0.9%). First, a pilot study was conducted to assess acute responses (48 h) to a near-isotonic solution (0.8% NaCl, i.e., 8 g NaCl/kg) and to inform sampling times for the main study. In the main study, 18 multiparous cows (208 ± 22 d in milk, 35.5 ± 4.7 kg milk yield/d) were assigned to 3 drinking water treatments in a breed-stratified, 3-period crossover design using a replicated 3 × 3 Latin-square treatment allocation: fresh water, medium salinity (4 g NaCl/kg), and high salinity (8 g NaCl/kg). Cows were allocated to one of 3 treatment sequences, ensuring that each cow received all treatments over 3 consecutive 14-d periods. Blood, urine, and fecal samples were collected at 14 h, 22 h, and 14 d in each treatment, and data were analyzed using linear mixed-effects models. Plasma osmolality increased, and total plasma protein concentration decreased within 14 h following exposure to salt water but returned to levels observed in the freshwater treatment after adaptation. Water salinity did not affect milk yield, energy-corrected milk yield, milk osmolality, fat and protein concentrations, or somatic cell count. Fluid intake increased with increased salinity, accompanied by increased urine volume and urinary and fecal sodium concentrations. However, body weight, body condition score, or fecal dry matter remained unaffected. These results indicate that dairy cows can adapt to drinking water with near isotonic NaCl content without compromising production. The results are promising with respect to the potential use of brackish water as an alternative during periods of freshwater scarcity.