PROTEIN OR dEB, DO WE NEED TO CHOOSE?
Recognizing the importance of optimizing the dietary electrolyte balance and choosing the correct tool to achieve balance is key to achieving significant animal performance improvements and profitability.
In the same way that a serious athlete recognizes the importance of managing dietary electrolyte balance (dEB) so too should we see the benefits of managing the dEB of our animals. And yet, while diets are often balanced down to the last kilojoule and individual amino acid percentages, dietary electrolyte balance is seldom, if ever, automatically calculated as part of a formulation optimization result or even part of commonly used nutrient recommendations.
In tropical conditions, animals need to fight against high temperature. Panting respiration is an important reaction in the effort to cool the body by evaporative cooling through loss of water from lungs. Thirst is increased, more urine is excreted and with it key electrolytes. Animals are depleted in HCO3- from increased urine excretion and the loss of CO2 from hyperventilation. Blood pH balance is then endangered.
Animals will need to get HCO3- rebalanced to stabilize blood pH. HCO3- ion will be absorbed by the intestinal cells according to the cations-anions gradient. HCO3- anions are using the same pump as Sodium and Potassium to pass the cell transporter. To increase absorption of bicarbonate anion, we need to provide sufficient Sodium and Potassium cations and reduce Chloride anion to the ration. Without proper supply of HCO3- anions together with Na+ and K+, we are taking the risks to see blood acidosis with a significant damage to animals performance.
To monitor this balance, scientists developed a formula commonly used by all nutritionists.
dEB (mEq) = Na/0,023 + K/0,039 – Cl/0,035, where Na, K and Cl is in g/kg dry matter.
To increase dEB value, we can either increase Sodium and Potassium or reduce Chloride or Sulfur. But each electrolyte does not have the same weight on the dEB results. The small divider applies to Sodium, and this is why the most common strategy to optimize dEB value focuses on Na+.
These electrolytes are integrally linked with fluid and acid-base balance in the organism. As such, they are part of the most tightly controlled physiological mechanisms in the body. Mechanisms that affect everything from bone density, heart and breathing rate, thirst, to nutrient absorption in the intestine to mention a few. This explains why adjusting dEB by just 100-120 mEq can give performance gains of 4-7%. This is a significant performance enhancement achievable at much lower cost compared to many feed additives.
The meta-analysis presented above shows a similar correlation between the evolution of dEB and blood pH, concentration of HCO3- in the blood, feed intake and ADG performance. All these graphs show an optimum around 200 meq / kg of feed.
Actually, the optimal level of dEB will depend on the animal and physiological stage.
When focusing on laying hens, we are noticing a tight correlation between the level of dEB and the eggs shell thickness. Without proper supply of Na+ and K+, laying hens will not be able to mobilize sufficient HCO3- to guarantee proper shell synthesis. When observing shells problems in laying farms, nutritionists need to careful look at the dEB of the diet, especially during hot weather.
Nobakht et al. (2006)
At times when everybody is looking at replacing gross protein content by digestible amino acids to reduce undigested portion of proteins and limit proteolytic fermentation in the colon, nutritionists need to pay a special importance to dEB. Indeed, proteins are coming with high level of potassium, and they were contributing to maintain high dEB. When proteins content is reduced, the level of dEB may become critical.
The table below reports a very interesting trial organized by INRA France. The first column illustrates a classic piglet trial where Soybean meal represent the major contributor in protein and in dEB (through potassium). In the second column, when we are replacing part of the soya by synthetic amino acids, the dEB is going down to only 111meq/kg endangering the performance.
*4 diets formulated with Iso digestible Aa and net energy.
If we set 175 meq as the minimum dEB, the computer has two solutions, either increasing again soyabean meal or using an alternative sodium source to increase dEB without having to increase gross protein. In conclusion, nutritionists who are looking at improving protein digestibility of their diets, need to set a minimum dEB if they do not want to affect performance. The only way to do so would be to offer alternative sodium source.
The cheapest and most popular source of sodium is sodium chloride. But each molecule of sodium comes with a molecule of chloride which will actually degrade the dEB.
The other solution would be Sodium bicarbonate. While this approach does deliver a source of sodium, it also delivers nutritionally unwanted effects. Particularly undesirable is the buffering capacity of sodium bicarbonate in the stomach, which is especially unwelcome in young animals such as weaning piglets whose intestinal tracts are immature.
As is commonly known, this buffering effect is caused by the addition of sodium bicarbonate to an acidic environment such as the stomach, which neutralizes the acid. This in turn increases the gastric pH and releases CO2 and water. It is precisely this effect that is capitalized upon when we use sodium bicarbonate-based antacids to get relief from our own heartburn or indigestion symptoms, whose instant relief is usually signaled with a satisfying eructation of CO2 – we burp. However, for our animals, this mechanism has several negative nutritional implications. Firstly, an increase in pH negatively affects the key proteolytic enzymes. Pepsinogen requires a low gastric pH to convert to pepsin and pepsin in turn has its activity optimum at a pH 2 and ceases to function above pH 6.5. Secondly, any commercial acidifiers added to the diet will effectively be neutralized by up to 30% by sodium bicarbonate
We therefore need to select a source of sodium that does not bring chloride nor bicarbonate. We may need to re-evaluate the interest as well of using sulfate-based products. As mentioned in the dEB formula, the presence of sulfate in the diet is negatively affecting the dEB value. The latest source of oxide launched recently on the market provide a similar and often better nutritional, bioavailability and even pharmacological performance than sulfates without affecting negatively the dEB