Water is one of the most basic, yet important things we can supply for our cows. Despite the central role that water plays in mammalian physiology, we tend to take it for granted.

It is even more crucial for our cows, which produce large quantities of milk that is roughly 87 percent water. All too often, we fail to provide this crucial nutrient in adequate quantities or acceptable quality for our cows. This article will provide some new insight into the fate of inorganic minerals and the potential effects that minerals in water can have on rumen function and metabolism.

Water chemistry and mineral speciation
Pure water is a very simple compound. However, as soon as anything is added to it, such as minerals in groundwater, its chemistry becomes very complex. A water analysis tells us the quantity of certain minerals in our water. Usually, we accept that information at face value. However, there are a couple of laws in water chemistry that must be obeyed. One law is electroneutrality. In other words, the electrical charges from ions, positive and negative, must be balanced so that water does not carry an electrical charge. The second law is that water will achieve the lowest possible energy state. This condition is met by matching the “strength” of the ionic bonds. As soon as another mineral is added to the solution, all of the mineral molecules, calcium carbonate or sodium chloride for instance, will split apart and recombine into different molecular combinations, called ion specie, until these two conditions are achieved.

The rumen, containing an aqueous solution in which fermentation occurs, is bound by the same electrochemical principles. We provide certain minerals in feed in the belief that they survive intact to be absorbed by our cows. Regardless of the source of inorganic minerals, whether they come from water or feed, they are subject to this process of dissociation and recombination in order to meet the electrochemical requirements. Table 1*provides a list of the various ion specie which are formed from some commonly fed inorganic minerals once they hit the aqueous environment of the rumen. One important consideration that follows is that each of these ion specie has a different solubility in the rumen and intestine. Absorption and use by the animal will largely depend on the ion’s solubility as it passes through the intestine. In the reference book Mineral Tolerance of Animals, the U.S. National Research Council concluded that simply knowing the concentration of a mineral in water or feed really tells us nothing of its speciation or solubility and hence its availability to the animal or potential for toxicity.

What about the minerals in water?
For years I have observed the impact that different water sources can have on cows. Sometimes it seems to be the high sulfate, sodium, iron, manganese or others. Sometimes it’s a high (pH 9) or low (pH 4) pH of the water that seems to put cows off. The results are often similar, regardless of the mineral(s) involved: Cows have lower-than-expected dry matter intake (DMI), milk production isn’t where it ought to be, and feed efficiency is poor. Sometimes reproduction or general health is affected. Unfortunately, it has been nearly impossible to define a cause-and-effect relationship between the specific minerals in the water and the symptoms of poor performance. There is very little research data on the effects of isolated minerals coming from water. On the other hand, making changes to the water supplied to cows, either through treatment or a change of source, has often yielded significant water intake and milk production responses.

As I dug into water chemistry in an attempt to understand these effects, I came across the concept of the Strong Ion Difference (SID) in solutions. At its core, the SID concept states that the pH of a solution will be driven by the sum of its cations, positively charged ions like calcium, minus the sum of its anions, negatively charged ions like chloride. SID is calculated based on (Na+K+Mg+Ca) – (Cl+S+P) and is reported as milliequivalents per liter. If the SID is positive, it will drive pH of the solution higher – more alkaline. If SID is negative, it will drive pH of the solution lower – more acidic. A solution with a SID of 0 will have a pH of 7, or neutral.

You have probably heard of or used the concept of dietary cation anion difference (DCAD) for your prefresh or lactating cows. DCAD is just the ruminant nutritionist’s version of SID, based on the exact same concept. A negative DCAD will drive cows toward metabolic acidosis. A negative DCAD and the resulting mild acidosis helps the prefresh cow mobilize calcium in preparation for lactation. A positive DCAD will drive cows toward higher blood and rumen pH and, for lactating cows, optimize DMI and milk production. To really understand the whole picture of cation anion balance, we need to apply the SID concept to water supplies and evaluate their contribution to DCAD and the potential effects on rumen and cow health.

We are proposing that the SID of water should be considered along with the DCAD in what we are calling the Total Intake Cation Anion Difference (TICAD). (See Figure 1*.) In many cases, the contributions of water to the TICAD will be minimal because the strong ion difference will be close to 0. In other cases, where the strong ion difference is large, +/- 10 milliequivalents per liter or more, the contribution to the TICAD can be significant and shift cows out of an optimal range.

The target TICAD should be in the same ranges as we’ve used for DCAD, between -8 to -12 milliequivalents per 100 grams DMI for prefresh cows, and between +30 to +40 milliequivalents per 100 grams DMI for lactating cows.

One recent example may help illustrate the concept. A water sample from the U.K. had a SID of +14 milliequivalents per liter due to a high level of sodium in the water. When combined with the DCAD of 32 milliequivalents per 100 grams DMI, we would expect the cows to move toward a higher rumen and blood pH. When the veterinarian performed rumenocentesis on several cows to check rumen pH, suspecting acidosis since the cows weren’t doing very well, he instead found that rumen pH was quite high, averaging pH 7.0. Removal of some of the added salt in the diet helped move cows back into a more optimal TICAD range. At the same time, that water supply with a strong ion difference of +14 milliequivalents per liter, was working against their efforts to avoid milk fever by providing an anionic diet with a negative DCAD.

Conclusion
Water is essential to the health and productivity of the animals in our care. There are numerous factors intrinsic to our water supplies, which can have substantial effects on our cows. Getting a water analysis is just the first step in assessing water’s impact. Evaluating the water supply in terms of mineral levels and their contribution to the strong ion difference will help you understand the potential impact on your cows.

Just because we may not see, smell or taste a problem in a water supply does not mean that no problem exists. The mineral content of water, when combined with the minerals we supplement in feeds, can dramatically alter the form and availability of those minerals. Taken together, the strong ions from both water and feed will influence rumen function and the acid/base status of the whole cow with implications for her health and productivity. We really should know more about water – the most important nutrient we supply to our cows.

In future issues, I’ll discuss some treatment options you can draw on if you determine there’s a problem with your water supply. PD

Figure and Table omitted but are available upon request to editor@progressivedairy.com.

Charlie Elrod
Springfield Farm Enterprises Inc.
Animal Nutrition
celrod@sfetech.net

Dr. Charlie Elrod for Progressive Dairyman