In Part 1 of this series, we looked at individual components and formulation of electrolyte solutions based on the calf’s needs, drawing heavily on Dr. Geoff Smith’s chapter from Veterinary Clinics of North America, 2008. This installment explores relationships between dehydration therapy and acidosis, and practical strategies for delivering effective electrolyte solutions.
Almost all calves that have diarrhea will develop acidemia and metabolic acidosis. Correcting this acidosis is an important function of a well formulated oral electrolyte solution. Calves can be rehydrated but still suffer from metabolic acidosis. For this reason, it is important to add an alkalinizing agent to the electrolyte formulation, such as bicarbonate, acetate or propionate. Bicarbonate is effective as an alkalinizing agent in its original state, while acetate and propionate have to be metabolized in the liver to become effective. While this process is somewhat slower, there seems to be no major difference between these types of products for correcting metabolic acidosis in the calf.
Bicarbonate will lower the pH of the abomasum. If feeding whole milk, this will interfere with the normal clotting of the milk. Most milk replacers use whey protein as the protein source and these proteins do not form a clot in the abomasum, so bicarbonate will not have an effect on these types of milk replacers. Also, low pH in the abomasum is an important deterrent to bacterial pathogens such as E. coli and Salmonella. These pathogens are susceptible to a low pH and most are prevented from passing on into the small intestine if a low abomasal pH is maintained.
Acetate and propionate do not lower the abomasal pH, while also facilitating the absorption of sodium. When metabolized in the liver, these volatile fatty acids are also an energy source, which bicarbonate is not. They will not interfere with the normal milk clotting process of whole milk.
A thorough discussion of strong ion difference (SID) is beyond the scope of this article, so only the basics will be discussed to help the practitioner be able to advise their clients on what products would be most beneficial to use. This approach to correcting acidosis uses the calculation of [Na+] + [K+] – [Cl-] = SID. Dr. Smith recommends a SID of 60-80 mEq/L. Even though it is theoretically possible to correct metabolic acidosis without an alkalinizing agent and a strong SID, Dr. Smith recommends that the electrolyte contain both, thus resulting in a faster resolution of the metabolic acidosis.
Some electrolyte formulas contain Psyllium or some other gelling factor. This will slow gastric emptying as well as absorb fluid from the intestine. However, this does not have an effect on rectifying dehydration since the fluid is still in the intestinal lumen and not in the ECF. It is generally not recommended to use these types of agents for this reason. These products will often result in less volume of diarrhea, giving the caretaker the impression the calf is improving, when in fact the process of improving hydration is not progressing.
Ideally, administration of oral electrolyte solutions should be spaced evenly between milk feedings to gain the maximum benefit of rehydration. This is often difficult to implement from a management aspect. Milk feedings are rarely spaced evenly apart. If feeding two times a day, it is common that the two feeding are actually spaced less than eight hours apart so one shift of employees can handle both feedings. This results in periods of more than 16 hours before the next morning feeding. The electrolyte feeding should be administered midway between the two milk feedings. The ideal situation would be to feed oral electrolyte solution twice, between the two feedings and after the last feeding, as far apart as possible. However, this rarely happens without having at least two shifts of employees working in the calf operation.
It is also advisable not to mix the oral electrolyte solution with milk or milk replacer. Milk products also have an osmolarity, and when mixed with an oral electrolyte solution, this will increase the osmolarity of the combination, likely resulting in an extremely hypertonic solution that could exacerbate the diarrhea problem. If the electrolyte solution has to be fed close to the milk feeding, it might also be advantageous to feed the milk replacer reduced to 12 to 12.5% solids if currently feeding an increased level of solids, which could also result in a hypertonic environment in the intestine.
There are some common mistakes that are made in the treatment of calf diarrhea. One is discontinuing the feeding of milk during treatment. Milk is the major source of nutrients for the calf and also its immune system. If treated correctly, most calves should be able to maintain a positive weight gain during a bout with diarrhea. Another is the use of oral antibiotics to treat all cases of diarrhea. In general, unless the calf has an elevated temperature, oral and systemic antibiotics are contraindicated. This will have a significant negative effect on the microbiota of the gastrointestinal tract, which is important in maintaining the mucin layer of the gut lining, maintaining the gut-associated immune system, competitive inhibition of pathogens and digestion of nutrients passing into the small intestine.
Following is a summary of the general recommendations of a well-formulated oral electrolyte solution:
- Sodium Concentration 90-130 mmol/L
- Chloride 40-80 mEq/L
- Potassium 10-30 mmol/L
- Osmolality 500-600 mOsm/L
- Strong Ion Difference 60-80 mEq/L
- Contain one or more alkalizing agents: Bicarbonate, acetate, propionate
- Glucose 2-3 grams per kg body of the calf
- Contain Glucose, neutral amino acids, and volatile fatty acids to facilitate sodium absorption
In his chapter in VCNA, Dr. Smith has an excellent summary statement:
“Practitioners should focus on selecting oral electrolyte solutions that satisfy the following four requirements: (1) supply sufficient sodium to normalize the ECF volume, (2) provide agents that facilitate absorption of sodium and water from the intestine, (3) correct the metabolic acidosis usually present in calves with diarrhea, and (4) provide energy. Additionally, the oral electrolyte should not cause any deleterious effects (such as abomasal bloat). Because veterinarians are often not directly involved with the administration of oral electrolytes to calves, it is important that they examine the electrolyte product being used in their clients’ herds and make recommendations when appropriate.”
Advising clients in choosing and administering appropriate electrolyte products to correct dehydration and metabolic acidosis is an area that is lacking in a high percentage of calf-raising operations. This would result in lower morbidity and mortality rate in young calves, and improve owners’ perceptions of the value of the veterinarian as an important source of information and advice for improving the calf health and profitability.
I would strongly recommend that anyone wanting to gain a deeper understanding of the pathophysiology of calf diarrhea and oral electrolyte therapy read Dr. Smith’s article in VCNA.
Find the first part of this article, and more dairy-nutrition information from Dr. Robert Corbett, in these articles on BovineVetOnline.