Farming Magazine - February, 2009


Dairy Nutrition: Essential Nutrient Number One

By John S. Hibma

There’s a lot to be said about water. Life would not exist without it.Cows need water—even in the dead of winter when daytime temperatures have a tough time getting above freezing. Lack of water is one of the most limiting factors in milk production—remember, milk is more than 75 percent water. In every gallon of milk, more than 3 quarts of it is water.

Quite often we forget just how much water a cow consumes during the course of a day. Not only is water necessary for basic metabolic functions, digestion of feed creates a lot of heat, as well. Just like the engine in your car needs coolant to stay cool, cows need water to keep their temperature under control. On a cold winter day, a cow producing 50 pounds of milk needs to consume about 15 gallons of water; a dairy cow producing 70 pounds of milk on a hot summer day needs to drink almost 30 gallons of water. When considering the water needs of our cows, we really need to focus on two areas: the quantity of water and the quality of the water.

Addressing the quantity issue is fairly straightforward. You have to have a source and the means to get it to the cows: wells, brooks, streams, springs, pumps, electricity, pipes, watering tanks and bowls and, in some cases, even a tanker truck load are what you need. So, to get the water to your cows it’s just a matter of doing it. Ironically, there’s more than one case of a dairy farm getting more milk out of its cows simply by making more water available.

Water quality issues are a little more complex because there are no clear guidelines to define water quality. When we consider drinking water for humans, there are maximums for things like nitrates, bacteria and carcinogenic chemicals. But, for most of the world’s population, the guidelines for water quality is simply, “If it doesn’t make you sick, you can drink it.”

Assuming the water that you offer your cows isn’t three parts dirt and one part water and the cows actually do drink it, the most pressing issue regarding water quality is the amount of dissolved minerals that it contains.

The Table 1 shows the minimum, maximum and average levels of 12 minerals in water taken from 32 locations around the U.S.

Ironically, there’s more than one case of a dairy farm getting more milk out of its cows simply by making more water available.

What really stood out with this data is the chlorine and sulfur levels in some of the samples. Chlorine ranged from 0 to 692 ppm and sulfur ranged from 1.2 to 1,020 ppm. Chlorine is usually present in water in the form of chloride, and sulfur in the form of sulfate. Both high chloride and high sulfate levels are known to affect palatability of water for cows. Most of us will agree that excessive chloride in our water doesn’t taste all that great, and high sulfates will give the water an odd, salty taste. Cows don’t care for it either.

We also need to keep in mind that chlorine and sulfur are both anions and have a significant impact on the DCAD balance (Dietary Cation/Anion Difference) in a feed ration. It’s important to know what these levels are in the water that’s being offered to the dairy herd. Many nutritionists today recommend that the DCAD balance for milk cows be fairly cationic, meaning that the ration contributes buffering to both the rumen and the blood. High levels of both of chloride and sulfate in the drinking water will prevent the ration from attaining the proper DCAD level.

High chloride and sulfate levels in the close-up cow diets have the potential to be even more problematic. Cows that are close to calving require a DCAD balance that is very close to zero, or even slightly negative. In many diets that include high levels of potassium in the forages, it sometimes becomes necessary to use an anionic salt, which is quite often a combination of chloride and sulfate, to reach the desired DCAD level. The additional chlorine or sulfur in the water could have the net result of driving the DCAD level much lower than what is desired for the diet.

Table 2 is a water sample I took from a dairy farm in Connecticut this past summer, which was analyzed by the Dairy One Forage Analysis Lab in Ithaca, N.Y. The herd has some on-going health and production issues that have been difficult to solve. Perhaps some of the problems can be traced back to the water.

The sample came back normal in all areas except two: both iron and manganese are about 10 times higher than they should be. A cow that would consume 20 gallons of that water every day would be consuming about 250 mg of iron—on the high side of recommended total dietary daily levels. Any iron found in feedstuffs would be added to this.

Iron, as we know, is highly reactive with oxygen and is essential for the transport of oxygen in blood. Because iron reacts with other minerals besides oxygen, too much iron in the diet will cause copper, selenium and zinc deficiencies. Besides the palatability issue, iron will also bind with certain bacteria creating a slimy buildup in buckets and watering troughs.

High levels of manganese will not affect a cow’s health, but it forms a thick, black sludge if there’s too much. Aside from the staining and sludgy buildups in watering troughs, the only problem with high manganese is the palatability of the water.

Whether the iron and manganese levels in this dairy’s water are solely or in part responsible for health and milk production challenges remains to be decided. Not only do the mineral levels themselves have to be considered in the water your cows drink, the types of interactions between those minerals must also be considered. The presence of too much of one mineral may limit the absorption of another. Since cows require so much water every day, not only is it imperative that clean, fresh water is made available, it’s important to know the mineral content of the water your cows are drinking.

The author is a dairy nutritional consultant and works for Central Connecticut Farmer’s Cooperative in Manchester, Conn.