CAN BLOOD BE ACID ?
From : Shutterschock
Last month, we presented an article about the stomach pH. This month, we will address the mechanisms involved to maintain the blood pH and how feed is influencing it. The mechanisms presented are very relevant in tropical climate as South East Asia and we are underestimating their importance when we are formulating feeds in our part of the world I hope that you will find the information below useful !!!
Maintenance of blood acid-base equilibrium is fundamental to life. Enzyme systems, metabolic functions and performance measures depend on this equilibrium. The pH of blood is maintained in the range 7.3 – 7.5 by buffer systems based essentially on HCO3- (bicarbonate ion). 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 in order 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. In case, we want to slow down absorption of bicarbonate anion, we should reduce supply of cations and increase anions. To optimize metabolism and maximize animals’ performance, it is critical to monitor the balance of dietary cations (positively charged ions) and anions (negatively charged ions). The dietary electrolyte balance (dEB), also known as cation-anion difference (CAD), is calculated using only monovalent ions (that is, sodium, potassium, and chlorine).
Equation - The equation below is the most widely used form of dEB taking into account the results of feed analysis regarding contents in (Na), potassium (K), and chlorine (Cl).
dEB (mEq/kg) = [Na(g/kg)/23 + K(g/kg)/39 - Cl(g/kg)/35.5]
Diets with low dEB are more likely to cause metabolic acidosis than diets with high dEB. Metabolic acidosis has been implicated with reduced feed intake and low growth performance. Dietary electrolyte balance may also affect energy, amino acid, vitamin, and mineral metabolism.
For example, excess dietary alkalinity (positive dEB) may increase lysine oxidation and, thus, increase the requirement for lysine.
For optimal animal performance, we should look at formulating feed to reach the following dEB.
The table clearly underlined the needs for increasing dEB during hot season in order to minimize the impact of heat stress on growth performance. High dEB will neutralize metabolic acidosis. This will help animals to maintain high feed intake to maintain growth performance. During gestation, it is important for the sow to have a high supply of cations to encourage the storage of Calcium in the bone. To promote an effective fixation of Ca2+ cations, we need to supply a high level of Sodium and Potassium cations in the feed to maintain cations balance in the blood. At the opposite, the situation changes when we are approaching farrowing. During the peripartum period starting 2 weeks before farrowing and running until 1 week after, the sow needs to release Calcium from the bone to the blood for two essential purposes; for uterus tonicity during the farrowing and for producing milk. To encourage this release, the supply of cations through the feed should be limited. This reduction of dEB correction will help to reduce the parturition time, avoid milk fever and increase milk production. Such approach would increase number of piglets alive. In parallel, the reduction of dEB will result as well in reducing sow urine pH. More acidic urine will prevent bacterial development and limit MMA syndrome. That favours better piglet health environment and longer sow utilisation.
During the lactation, the priority is made on feed intake. Heat stress is a major issue for lactating sow as it is depressing intake at a moment when requirement are the highest. An increase of feed dEB will stimulate feed intake and milk production. That will increase piglets weight at weaning while ensuring a good shape of the sow at weaning for the next cycle. For Aquaculture, little studies have been made on the effect of dEB on fresh water fish. Y.Dersjant-Li and J.A.J Verreth studied several level of dEB various (-100 mEq, +100mEq, +500mEq and +700mEq) on Catfish and they concluded that optimal growth and feed conversion were obtained at 700mEq. More studies on other species would be required to get clear conclusion of optimal dEB.
In order to adjust the feed dEB in line with the table presented above, the following recommendations would need to be assessed by feed manufacturers.
Adjust the balance between Sodium Chloride and Sodium Formate to modify Sodium and Chloride level independently. Sodium formate increases the dEB with about 15 mEq for each kilogram added to feed.
Adjust Sodium Bicarbonate dosage in the feed formula, especially in lactating feeds to provide sufficient buffering for blood.
For Swine feed millers, it may be required to develop a special feed for peripartum in order to provide the right dEB and optimize farrowing performance.