COMBATTING DEHYDRATION IN CALVES

Morbidity and mortality rates in U.S. dairy calves is high, and a large proportion is due to digestive issues. Calves with at least one morbidity incidence were reported at 33.8% and mortality at 5%. Digestive issues account for 50.9% of the reported morbidity rate and 32% of the mortality rate (USDA, 2021). There are four major infectious causes of diarrhea in calves, Enterotoxigenic Escherichia coli (ETEC), Cryptosporidium parvum, rotavirus and coronavirus. The pathophysiologic mechanisms of infectious diarrhea can be due to malabsorptive, maldigestive, and secretory effects (Foster and Smith, 2009), or increased permeability of the intestines (Costello, 2011).

Increased intestinal permeability occurs when microbes induce inflammation and damage to the intestinal epithelium, allowing greater water movement into the small intestine. In contrast, hypersecretion refers to an increase in water secretion into the intestinal lumen without direct epithelial damage. Malabsorption results from epithelial injury that reduces the intestine’s ability to absorb nutrients and water. Consequently, undigested nutrients bypass the small intestine, promoting bacterial overgrowth and excessive production of volatile fatty acids (VFAs). These changes alter intestinal osmolarity and contribute to fluid loss. Lastly, maldigestion is commonly associated with sudden dietary changes, poor-quality ingredients, food allergens, or digestive disorders, and often occurs concurrently with malabsorption. Collectively, these mechanisms can lead to substantial fluid loss due to alterations in extracellular fluid osmolarity (Costello, 2011).

Calves that show no clinical signs of dehydration can lose as much as 6% of their body weight in fluids, while those that show signs of lateral recumbency, have cool extremities, a poor peripheral pulse, and are comatose can lose 10-14% of their body weight in fluids (Costello, 2011). Therefore, rehydration therapy is required to replace fluid losses and restore blood pH (Foster and Smith, 2009). Administration of intravenous or subcutaneous fluids, such as hypertonic saline and dextrose, increases plasma volume and is a method of fluid therapy. Although this is short lived, administration of an isotonic oral electrolyte solution is also recommended. The amount of electrolyte solution offered depends on the state of the animal and should be offered in between milk feedings to provide an even distribution of fluids throughout the day (Costello, 2011). A general recommendation is to provide an oral electrolyte solution to calves at the first sign of scours less than 21 days of age, due to the unpredictability of how quickly and severe dehydration can develop (Constable et al., 2021). Clinical signs can be scored to determine the severity of diarrhea and when to administer an electrolyte solution. This includes fecal consistency, clinical depression, dehydration, posture, behavior, palpebral reflex, suckling reflex, degree of enophthalmos and fetlock temperature (Walker et al, 1998; Dore et al, 2019; Trefz et al, 2012; Constable, 2021). Dore et al. (2019) began electrolyte therapy for calves with a fecal consistency score of 3, hydration score of 2 and a depression score of at least 1. The fecal scoring system was on a 0 to 3 scale, with 3 equaling severe diarrhea (pure liquid), the hydration scoring system was on a scale of 0 to 2, with 2 equaling moderate dehydration (skin tent >3 s but <10 s, eyes moderately recessed into orbit) and lastly a depression scoring system of 0 to 3, with 1 equaling mild depression (calf suckles but not vigorously).Therefore, the recommendation is that the total fluid requirement is 12% of the calf’s euhydrated body weight or greater daily, including milk feedings. This includes at least 24 hours of treatment of two milk feedings and an oral electrolyte feeding, with further administration of treatment in calves with watery diarrhea, to monitor response to treatment (Constable et al., 2021).

There are four key requirements of an oral electrolyte solution. It must provide a sufficient supply of sodium to normalize the extracellular fluid volume and provide an agent (glucose, citrate, acetate, propionate or glycine) to facilitate sodium and water absorption in the small intestine. It should provide an alkalizing agent (acetate, propionate, bicarbonate) to correct the acidosis in the bloodstream and provide a source of energy, as diarrheic calves are usually in a state of negative energy balance (Smith, 2022).

Lastly, any form of fluid therapy should be considered based on the effective strong ion difference (SID) of the solution. This consideration is important in correcting the acidosis the calf is experiencing due to dehydration. An SID in plasma represents the difference between the cations (Na+, K+, Ca2+, Mg2+) and the anions (Cl-, L-lactate-, D-lactate-, sulfate2-, ketoacids, non-esterified fatty acids). This directly alters the blood pH and changes the acid base balance (Constable, 1999; Constable, 2000; Constable, 2002; Constable, 2014). An effective SID of an oral electrolyte solution may range from 40-80 mmol/L (Sen et al., 2006), and an optimal effective SID may be 60 mmol/L (Smith and Berchtold, 2014). Additionally, osmolarity of the solution should be considered. The recommended sodium concentration of the solution ranging from 90-130 mmol/L (Smith, 2022). In a study by Wilms et al. (2019), where they administered an oral electrolyte solution with a sodium and dextrose concentration greater than 100 mmol/L, to calves without ad libitum access to water. This increased the duration of diarrhea in the calves. The researchers administered electrolytes in both water and milk replacer, the solutions were considered hypertonic, with an osmolality of 504 mOsm/kg and 704 mOsm/kg respectively. Highlighting the importance of this consideration and the need for ad libitum access to water.

Overall, choosing a form of fluid therapy is individualized reflecting the physiological status of the calf and management decisions of the farm. As diarrhea is a complex and significant health challenge during the preweaning phase. The goal is to choose a solution with the appropriate concentration of sodium, alkalinizing agents and an effective SID to correct the dehydration and metabolic acidosis that the calf is experiencing. While administering electrolytes in a timely manner to affected calves, as a common mistake is to wait too long. The calf should be offered electrolytes throughout the duration of the scouring event (Costello, 2011).

— Victoria Blaney

vblaney@whminer.com