Editor’s note: This article was written by Craig Thomas, extension dairy educator with Michigan State University and first appeared in the Michigan Dairy Review.
Dairy producers spend a great deal of time, effort and money ensuring that dairy cow rations are fine-tuned to the “nth” degree. A few milligrams of this, a few parts per million of that, all to ensure that no stone goes unturned in the quest for the perfect ration. Unfortunately, in the process the most important nutrient of all often goes barely noticed and only lightly considered. What nutrient? Water.
Recall that water weighs 8.35 lb/gal Even though we normally don’t think in such terms, water by weight, is the largest component of the daily ration for all classes of dairy animals (see Table 1 below). This is particularly true of the milking cow. If you consider her total ration, it will contain somewhere around 50-60 lb of dry matter (DM) per day in the form of what we normally think of as “ration” (carbohydrates, proteins, fats, vitamins, and minerals).
But, just as importantly or even more, the ration also consists of about 42 gallons of drinking water. When you convert the total water consumption to weight the milking cow is consuming around 420 lb of water per day (42 gal. drinking water X 8.35 lb/gal + 120 lb as fed ration X 55 percent water = 350.7 lb drinking water + 66.0 lb water from feed = 416.7 lb total water intake per day). That means that the dry matter intake we usually focus on accounts for only about 12 percent of the cow’s total nutrient intake; while water accounts for about 88 percent. In fact, the water requirement of a lactating dairy cow on a per pound of body weight basis is the highest of any land-based mammal (10).
How Much Attention Does Drinking Water Receive on Your Farm?
Drinking water should receive your attention in two regards: 1) water quality (Is your water fit to drink based on its chemical and mineral composition?”), and, 2) water delivery (Are you providing an ample supply of good quality, fresh, clean water to your cattle?).
According to Michigan State University’s Dr. David Beede (1, 2) the most important constituents to evaluate in regards to water quality are: total dissolved solids (TDS), sulfate (SO4), chloride, (Cl), iron (Fe), and nitrate-nitrogen (NO3-N).
Total dissolved solids measures the sum of all inorganic matter dissolved in water (9), and is an indicator of the salinity of water (1, 2). Experts usually recommend that TDS levels above 1,000 ppm should be investigated further and potentially be corrected to prevent and/or correct problems like diarrhea and dehydration (4).