Do you know which land-based mammal has the highest daily drinking water requirement (per unit pound of body weight)? Elephant? Rhinoceros? Hippopotamus? These may be good guesses, but the answer is the modern dairy cow. A milking dairy cow drinks about 30 to 50 gallons of water each day. During periods of heat stress water intake may double. Water weighs 8.35 lbs/gal, so a milking dairy cow may consume as much as 420 (or more) pounds of water daily. Thus, the intake of water on a per pound basis is far greater than that of protein, carbohydrates, fats and minerals a cow consumes in what we normally think of as “ration.” This means what we usually focus on (dry matter intake) accounts for only about 12% of the cow’s total nutrient intake; while water accounts for about 88%! Thus, water IS the most important nutrient in a cow’s total daily intake.

Armed with these facts, how much focus should drinking water receive on your farm? The first water criterion you should examine is drinking water quality. Is your water fit to drink based on its chemical and mineral composition?”). In this regard, Michigan State University dairy nutritionists tell us that the most important constituents to evaluate are: total dissolved solids (TDS), sulfate (SO4), chloride, (Cl), iron (Fe), and nitrate-nitrogen (NO3-N). Therefore, it is important to have a laboratory analysis done for your cows’ drinking water.

TDS: measures the sum of all inorganic matter dissolved in water, and is an indicator of water salinity. Levels above 1,000 ppm should be investigated further and potentially be corrected to prevent and/or correct problems like diarrhea and dehydration.

Sulfate + Chloride: if the combined SO4 + Cl content of drinking water is greater than 500 ppm further testing and evaluation also are needed. At these, or higher levels, these minerals may lead to health and production problems.

Nitrate-nitrogen: nitrate-nitrogen levels in drinking water should not exceed 20 ppm. High nitrate-nitrogen levels have been associated with long term reproductive problems in dairy cows; such as higher services per conception, lower first service conception rates, and longer calving intervals.

Iron: cow drinking water containing over 0.3 ppm iron may cause subclinical chronic iron toxicity, or more severe problems. Most dairy rations provide adequate iron. Thus, when drinking water contains excess iron (soluble iron called ferrous-iron in drinking water) the total iron may rise in the cow’s tissues causing “oxidative stress.” This may lead to a host of problems including increased retained placenta, mastitis, metritis, and a general compromising of the animal’s immune system. Excess soluble iron in the animal’s gut also ties-up and reduces absorption of other key minerals like zinc and copper.

Excess content of these mineral constituents in water may also contribute to problems with your farm’s water delivery system (i.e., pumps, pipes, etc.) and decrease the effectiveness of cleaners and sanitizers (e.g., pipeline cleaning and sanitizing). The later could lead to milk quality problems (e.g., increased bacteria counts) and buildup within pipes that restrict water flow.

Future articles in this series will continue examining the importance of drinking water to a dairy cow’s diet.