Diarrhea is a major problem in calves less than one month of age and is of tremendous economic importance. Diarrhea results in electrolyte imbalance, dehydration, and metabolic acidosis [16–20]; however, only a few studies available have focused on acid−base balance, serum chemistries, and blood gas parameters associated with diarrhea caused by infectious agents in neonatal calves [21, 22]. Unfortunately, because the information currently available for healthy young Korean native calves is not well documented, reference values for adult cattle have commonly been used to direct therapy. In our study, we examined electrolytes, serum chemistries, and blood gas parameters in both healthy and diarrheic calves through rapid and accurate field testing. The results showed that SID, pH, bicarbonate, and BE were significantly decreased, whereas BUN and AG were significantly increased in diarrheic calves compared with healthy calves. As such, these parameters provide both critical and accurate information for treatment and prognosis.
Our findings revealed significant changes in plasma electrolyte concentrations (Na+, K+, and Cl−) that varied according to diarrheic calf age. Our results documented an overall decrease in sodium and overall increase in potassium, chloride, and BUN concentrations in diarrheic calves when compared with healthy calves. The decrease in sodium concentration can be explained by increased intestinal loss ; this situation results in a concomitant decrease in plasma sodium concentration accompanied by an increase in chloride concentration.
Moreover, the significant decrease in SID values was identified in the diarrheic calves; this finding can be explained by the combination of hyponatremia and hyperchloremia . The decrease in SID represents the key role played by hyponatremia in this setting, which can be attributed to excessive loss of sodium into the gastrointestinal tract as well as decreased milk intake due to anorexia; the combination of these factors results in acidemia and strong ion acidosis [24, 25]. As such, this study highlights the role of strong ions in the acid−base status in diarrheic calves.
In addition, we detected increases in potassium concentration in diarrheic calves. Hyperkalemia has clinically been associated with acidemia and decreased intracellular pH due to electrolyte imbalance [20, 26]. While we did not include the results of packed red cell volume in these neonatal calves, we did note significant dehydration among the diarrheic calves aged 1−10 days, a finding that explains the hyperkalemia observed among diarrheic calves. Interestingly, BUN levels were significantly higher in the diarrheic calves when compared with the healthy calves, findings that are consistent with previous results [27–29]. The significant increase in BUN at all age groups was associated with a decreased glomerular filtration rate due to dehydration; this also contributed to the acidemia and metabolic acidosis observed . Taken together, our results suggest that potassium and BUN can be used as appropriate measurements for evaluating the severity of diarrhea in calves.
Blood gas analysis also provides valuable information for diagnosis, prognosis, and identification of therapeutic options . In this study, we observed significant alterations in acid-base homeostasis. Of particular note, bicarbonate levels were significantly lower among diarrheic calves compared to their healthy counterparts. This finding is closely associated with reductions in sodium and increases in potassium concentrations. The significant decline in bicarbonate in diarrheic calves is indicative of severe metabolic acidosis; these findings were associated with a marked decrease in blood pH as would be anticipated for acidotic calves . Our results reveal a correlation between pH and animal health and suggest that blood pH may be a useful indicator of clinical status of diarrheic calves.
We found that blood gas analysis is an important indicator for determining the prognosis of and setting treatment policy for calves. In particular, calves with severe diarrhea showed a pH of less than 7.1, a HCO3− value of less than 20, and minus value for BE. Therefore, calves showing such decreasing values were judged as having a poor prognosis, and intensive treatment was performed, or the calf was recommended to a clinician. Mild diarrheic calves (pH 7.2 ~ 7.4) can have their acidosis corrected with a lactated linger solution (Hartman’s solution) injection. However, severe diarrheic calves (pH < 7.1) could have their acidosis corrected with intravenous bicarbonate. To prevent the occurrence of metabolic alkalosis due to excessive administration of bicarbonate, BE value was used to determine an appropriate dosage.
Likewise, values calculated for AG were higher in the diarrheic calves than in the healthy ones. Changes in AG may be attributed to variations in unidentified strong anions that include D-lactate, ketones, phosphate, and inorganic anions [25, 33]. Although we cannot draw specific conclusions because concentrations of these biological acids were not measured directly in this study, we speculate that their levels may be increased in diarrheic calves . In addition, acidemia in hyperkalemic diarrheic calves was associated with a decrease of sodium and increase of AG .
Finally, BE values were significantly reduced in the diarrheic calves, which may contribute to the estimation of the degree of metabolic acidosis and clinical status. Of note, all calves evaluated in this study were able to stand and suck at feeding time but preferred to remain in sternal recumbency. This may explain the significant correlation among BE values, levels of dehydration, and metabolic acidosis. Consequently, on the basis of our results, we propose that calf health may be determined by blood pH, bicarbonate levels, and BE as opposed to the other parameters measured.
A limitation of our research is that we did not perform continuous follow-up studies with the diarrheic calves, and we could not exactly predict the factors associated with death in those with severe diarrhea. However, we believe it is meaningful to establish the biochemical and blood gas values of neonatal Korean native calves according to age and to compare these values with healthy and severe diarrheic calves, as we did in this study.