Fluid therapy is very much used when treating calves with diarrhoea. The cost and the time it takes to properly restrain a cow, administer the volume needed and monitor the animal make us often reluctant to correct fluid imbalances properly in adult cattle. It is necessary to discuss fluid therapy of mature cattle separately from fluid therapy of calves because the metabolic abnormalities commonly seen in mature cattle are quite different from those of calves and other species (Roussel, 2009). The underlying cause needs to be identified and corrected, but fluid therapy is often a key factor in the recovery process. The type of fluid, the volume and the route the fluids are to be given will help to correct circulatory collapse, electrolyte imbalances and base deficits.
Certain emergency conditions of adult cattle cause different degrees of fluid and electrolyte deficits and changes in the animal’s acid-base status. Often, it is not practical to perform laboratory analysis when working as a field vet. It would mean taking a blood sample, driving back to the surgery to analyse it and then back to farm to administer the right fluids. What we do know is that in adult cattle, conditions such as grain overload and choke (oesophageal obstruction) cause an acidotic state. We also know that gastrointestinal catastrophes such as abomasal volvulus and caecal or abomasal torsion result in a metabolic alkalosis (Roussel, 2009). Circulatory collapse is often a result of endotoxaemia caused by peracute Gram-negative bacterial infections, such as Escherichia coli mastitis, severe endometritis and septic peritonitis (Sargison and Scott, 1996). In these above-mentioned scenarios, correction of dehydration will often restore renal function sufficiently that electrolyte and acid-base imbalances will then self-correct.
When addressing hydration status, body weight and rumen fill can be misleading, as can skin tent time and eyeball recession – for example, animals in poor body condition will have skin that tents and retracted eyeballs, regardless of their hydration status (Pedersen, 2013). Clinical signs vary between the various degrees of dehydration in the adult ruminant (Table 1).
|DEGREE OF DEHYDRATION||CLINICAL SIGNS|
|Severe||Recession of the eyeball > 5mm|
Persistence of a skin tent on neck ≥ 7 seconds
Oral mucous membranes dry and cold
|Moderate||Recession of the eyeball > 5mm|
Skin turgor reduced
Persistence of a skin tent on neck 6 to 7 seconds
Oral mucous membranes dry and cold
Mucous membranes tacky
Persistence of a skin tent on neck ≥ 5 seconds
No visible recession of the eyeball
When deciding on route of administration it is also important to consider the cardiovascular status of the animal. In conditions such as acute toxic mastitis, abdominal catastrophes or severe endometritis, the gastrointestinal motility will also be substantially reduced. This makes oral fluid therapy less effective (Green, 1998; Hallowell et al., 2012). For this reason, IV fluids are often indicated once moderate to severe signs of hypovolaemia are seen.
Dehydrated adult cattle need huge volumes of isotonic fluids. This is time consuming and costly. Instead, hypertonic fluids offer a more practical option in the field situation. You can safely administer 4ml/kg to 5ml/kg over five minutes, equivalent to approximately 2 to 3 litres in a 650kg cow. Use of a 10G catheter and wide-bore giving set allows faster administration (Pedersen, 2013).
For cows in metabolic acidosis due to, for example, grain overload, alkalinising solutions are used. If we use 8.3% NaHCO3 solution, 3 litres are required. If we use 5% NaHCO3 solution 4.5 litres are required. If we use isotonic NaHCO3 solution, 18 litres are required to correct the acidosis (Roussel, 2009).
Most gastrointestinal diseases of adult cattle and many other causes of dehydration (with the exception of those mentioned above) are associated with metabolic alkalosis, hypokalaemia and hypochloridaemia. The degree of these changes may be mild (as in early left displaced abomasum) or severe (as in abomasus volvulus). If the gastrointestinal tract is patent and functional, oral rehydration is the method of choice. If obstruction, ileus or circulatory shock is present, intravenous fluids should be administered. Hypertonic saline (7.2% NaCl) solution may be used to correct dehydration and electrolyte abnormalities with smaller volumes of IV fluid. A 650kg animal requires 2.5 litres of hypertonic saline (Roussel, 2009).
Dextrose can be used in anorectic cows or those in ketosis. 500ml of 50% dextrose can be added to 5 litres of isotonic solution (Roussel, 2009). Calcium should be added in freshly calved dairy cows.
For the use of hypertonic saline fluids to be effective, it relies on the uptake of water from the rumen to restore circulatory volume. Cattle should be provided with a supply of fresh water immediately after treatment. Most cattle will drink 20 to 40 litres within 10 minutes. The animals that are not drinking should be rumen pumped (Pedersen, 2013).
The electrolyte solutions for intraruminal use should be isotonic or hypotonic to avoid suppression of dry matter intake. This means that we cannot use the same rehydration solutions for calves in adult cattle. These calf “lectades” are mostly hypertonic and alkalinising. This would increase the level of dehydration and alkalosis, consequently depressing the food intake. In most situations, an electrolyte solution containing sodium chloride, potassium chloride and calcium and magnesium salts is suitable.
The “stomach” pump has made the administration of oral fluids so much easier and quicker in adult cattle. Nowadays, a farm vet will feel lost without this piece of equipment. It takes only a matter of time to pump a cow with 20 to 40 litres of the appropriate electrolyte solution.
Oral fluids alone are not indicated in the recumbent dehydrated patient. Remember, if the rumen is distended with fluid, do not administer oral fluids. There is already an excess of fluid in the rumen in the face of dehydration. Adding more will only increase abdominal distention. The excess fluid should be removed if possible, the rumen alkalinised and intravenous fluid therapy initiated.
Oral fluids can prove beneficial in a variety of scenarios. In addition to cases of obvious fluid loss, such as diarrhoea and abdominal surgery, oral fluid therapy has also proved to be useful in cases of toxic mastitis, acute ruminal acidosis and immediately after calving (Pedersen, 2013). Administering oral fluids to dairy cows at risk of developing a left displaced abomasum is believed to reduce this condition. The rumen will be “weighed down” by the administered fluids, making it more difficult for the abomasum to pass under it. In the case of the fresh-calved cow a solution in which calcium rather than sodium is the major cation is preferable in order to reduce the risk of hypocalcaemia, and cases of ruminal acidosis require an additional alkalinising agent (Pedersen, 2013). Many commercial preparations are available to be mixed into water. They provide oral sources of energy and calcium, which can be useful in treatment of conditions such as ketosis and recurrent hypocalcaemia (Silk, 2014).
Another type of emergency fluid therapy is whole blood transfusion. It can be relatively simple to perform and clinically rewarding in carefully selected cases. Infection with Babesia divergens (red water), or following severe blood loss as a result of abomasal ulceration or severe trauma, may provide a suitable opportunity. No more than 25 percent of total blood volume should be collected from a healthy donor at one time. In practice, 10 to 15 percent of an adult’s blood volume (5 to 6 litres) is usually sufficient for most indications (Soldan, 1999).