Recent water use estimations in California dairy farms indicate 40 percent to 50 percent of water is used for animal cooling and consumption. Economic and regulatory constraints make it important to know the volume of water consumed and the mineral content of the water.

Two surveys carried out in Merced County on almost 100 dairy farms indicate that when animal drinking water has more than 500 milligrams (mg) per liter of Total Salts (TS), mineral content of the salts should be identified and included in the dietary mineral balance. Mineral content of drinking water is important to 1) adjust rations to meet animal requirements, 2) control, and in many cases reduce, intake of mineral supplements (feed cost), and 3) estimate mineral excretion and reduce manure production. For example, it was estimated that drinking water with a mean of 800±310 mg TS per liter provided 7 percent of calcium, 9 percent of magnesium, 25 percent of chloride, 25 percent of sodium, and 8 percent of sulfur that the animals required (for cows averaging 70 pounds of milk per day).

The National Research Council (NRC) suggests different formulas to estimate daily water intake of lactating dairy cows. One of the most recommended formulas was developed by researchers from the Department of Dairy Science, University of Illinois (Murphy et al. 1983).

Murphy’s equation is: WI = 15.99 + 1.58 x DMI + 0 .90 MP + 0.05 x SI + 1.20 x MT.

• WI = water intake (kg/cow/day)
• DMI = dry matter intake (kg/day)
• MP = milk production (kg/day)
• SI = sodium intake (g/day)
• MT = minimum temperature (°C)

*To convert kg to lb, multiply by 2.2*

Ten dairy farms were selected in Merced County to evaluate Murphy’s equation. Electronic flow meters were installed for variable periods of time, no less than two weeks in each dairy. Water consumption of lactating animals was measured in freestall barns. The daily total volume of water used was divided by the number of cows in each barn. A high correlation (R2=0.80) was observed between Murphy’s equation and the information provided by the flow meters, indicating that Murphy’s formula can be used to estimate water intake for California dairy cows.

Water is the most important nutrient for dairy cattle (NRC, 2001). Estimations of both water intake and mineral content of drinking water are important for balancing dietary minerals (when TS are > 500mg/liter) and to control mineral excretion in manure.

Source: University of California Cooperative Extension