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Redefining hydration: It’s more than just salt, sugar and potassium

Nathan Upah for Progressive Dairy Published on 14 May 2021

The importance of maintaining proper hydration in animals is widely understood; it has been instilled in us as a fundamental component to calf raising and maintaining life. However, oral rehydration electrolyte solutions (ORES) have walked the path of tradition for decades. The World Health Organization recommends salt, sugar, potassium and chloride be components of an ORES. Mix it with water and voila! Seemingly, the only real assessment to gauge the effectiveness of an ORES supplement required simply checking the box next to one question, “Did they drink it?”

Unfortunately, after the bucket has been emptied, producers can’t directly measure how well the ORES actually rehydrated the calf. We can use qualifiers such as brightness and vigor, but eyeball socket recession and skin tenting remain really the only practical means by which an observer can get a rudimentary handle on the severity of dehydration.



The time has come to redefine hydration. To provide a new definition requires new information, a new approach and new science to have the ability to bring new understandings and discovery to an old concept. Through innovation, boundaries are tested, concepts are evaluated and new conclusion are drawn.

Science has taught us that dehydration is more than just net loss of water. The event that is causing dehydration has a determining factor on what nutrients need to be replenished and the concentration necessary to restore nutrient balance. For instance, much work has been done to establish appropriate guidelines on what an ORES needs to supply in order to address the physiological challenges caused by scours. Among the crucial nutrient specifications, scouring calves require a blood alkalinizing agent, an optimal sodium concentration and a positive strong ion difference. When using an ORES with these specifications, recovery from scours has been proven to be more rapid and calf performance improved.

If a calf is severely scouring, it is not only losing water but also significant amounts of nutrients. Logic dictates that it would be advantageous to supplement with a very nutrient-dense ORES. The nutrient density of the solution, or more appropriately put, osmolarity, is the number of solids dissolved in a solution expressed as mOsm/L. Osmolarity is the reason you can’t drink salt water. It’s the reason you can’t double milk replacer powder in the same volume of water.

There are two terms to understand relating to osmolarity. An osmolarity level closer to that of blood (275-300 mOsm/L) would be considered an isotonic solution. A hypertonic solution (greater than 300 mOsm/L) not only carries more solids (nutrients), but it also more closely emulates the concentration of digesta at the villus tip in the small intestine where absorption occurs.

Unfortunately, the concentration of solids in the solution isn’t telling us how efficiently that solution will be absorbed, we just naturally assume more to be better. In fact, that’s not always true; more isn’t always better, but these are the types of science-driven concepts that are forcing us to change the way we think about hydration. A solution that is 400 mOsm/L actually could be absorbed as well as a solution that’s 300 mOsm/L.


Imagine two jars filled with coins. One jar contains 300 coins, while the second jar contains 400. Your task is to select the jar that will make you the most money. Naturally you’d select the jar with 400 coins. But when you open it, you learn the jar with 400 coins contained 400 pennies and the jar with 300 coins was 300 quarters. The types of ingredients in the ORES play a significant role in determining rehydration capability, not just the quantity of ingredients.

Nutrient absorption in the intestinal tract is not accomplished in a straight orderly fashion; rather it’s a dynamic, fast and even prioritized process that occurs through many pathways including specific transporters, gated channels and receptor sites. Almost all forms of nutrient uptake require water. Engaging as many of these nutrient transporters as possible can greatly influence the efficiency by which nutrients are absorbed and rehydration achieved.

Selecting ORES today is similar to blindly picking through those jars filled with coins. A tag with a nutrient analysis does not provide enough insight to see or understand the full picture; however, without a laboratory and scientific equipment, it is very difficult to really understand how an ingredient or product is going to rehydrate and replenish nutrients. Fortunately, there are key attributes to look for and questions to ask to know if your current ORES is providing your calf with what it needs:

  1. Are there alkalizing agent ingredients listed on the tag?
  2. What are they? Bicarbonate-based electrolytes buffer the abomasal pH but have minimal effect on blood pH.
  3. Can this ORES be fed with milk or milk replacer?
  4. Does this ORES have an amino acid? Amino acids, like glycine, require water to be drawn in and absorbed; activating that nutrient channel for absorption is important.

We’re repeatedly reminded that more effective hydration is needed. This becomes more paramount as our industry becomes further squeezed for labor resources, and we no longer can afford the time to supplement electrolytes two or three times per day. About 60% of pre-weaned calf mortality is due to scours and insufficient rehydration strategies to combat it. Rehydrating animals goes much deeper than salt, sugar and potassium. Science has given us the power to measure the effectiveness of an electrolyte solution that is many layers beyond the measure of what the naked eye (or label) can tell us. That hydration power has been harnessed, and yes it can still be tasty enough that they drink it too.  end mark

Nathan Upah
  • Nathan Upah

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