1Graduated from College of Agriculture, Shiraz University, Shiraz, Iran
2Department of Animal Sciences, College of Agriculture, Shiraz University, Shiraz, Iran
3Department of Animal Sciences, College of Agriculture, Esfahan University of Technology, Esfahan, Iran
Fourteen primiparous Holstein cows (180.0 ± 4.3 days in milk) with a mean (±SD) daily milk yield of 35.0 ± 1.3 kg and a body condition score of 3.2 ± 0.2 were allotted into two groups (n = 7), and were fed a ration consisting of (dry matter basis) 35% corn silage, 25% alfalfa hay and 40% concentrates. Salt was provided free choice. The experiment was performed during the period of heat stress, i.e., when the temperature-humidity index was greater than 72. One group was offered desalinated water containing 570 mg total dissolved solids (TDS) and another group was offered water containing 1400 mg TDS per L. Milk yield was measured weekly, and milk samples were taken on days 21 and 42 for determination of milk composition. Blood samples were taken on days 21 and 42 from the median caudal vein of the tail and the serum concentrations of Na+, K+, Ca2+, Mg2+, tri-iodothyronine (T3) and thyroxine (T4) were measured. Ruminal fluid was taken by rumenocentesis on day 42 for determination of volatile fatty acids (VFA) and pH. Milk yield, milk composition, serum concentrations of T3and T4, Na+, Ca2+ and Mg2+, ruminal fluid VFA concentration and pH were not significantly affected by water TDS (P>0.05); however, cows receiving desalinated water produced 2 kg more milk per cow per day. Serum K+ concentration was significantly higher in cows consuming saline water (P<0.05). The present data indicated that water with a TDS of 1400 mg per L had no adverse effect on lactating cows; therefore, it is not necessary to desalinate water in the region under study. However, in light of the possible effects of saline water on thyroid hormones, further studies concerning the influence of saline water on the metabolism of high producing cows in hot climates are warranted.