Cattle of all ages, when challenged from disease or dehydrating changes in environment or management, will either use body reserves of fluids to maintain homeostasis or attempt to replenish fluid balance by drinking water.
Fluids, including water, comprise an average of 60% of the total body weight of the dairy or beef animal. Young calves have about 5–10% more body fluid than the adult. Of this total body fluid, 66% is found in cells and the remaining third is found in the soft tissue compartment and vascular system.
The rumen serves as a reservoir which releases consumed water to the body fluid compartments through an osmotic pressure gradient. As cells require fluid for metabolism, electrolytes and other nutrients exert osmotic pressure to continuously supply the cells with fluid for normal functions. A body fluid deficit results in reduced perfusion of fluid transferred nutrients to the cells for metabolism. Management of the water content of the rumen should be employed to maintain both normal rumen fluid volume as well as other body fluid reserves to help cattle combat the dehydrating effects from disease, environmental stress or transportation water restriction.
Water intake requirements
To maintain normal cellular functions, the average water maintenance intake rate is 40–60 milliliters of fluid per kilogram of body weight daily. The average 100 lbs. of bodyweight require 1.2 gallons (9.6 lbs.) of water on a daily basis. If cattle consume 10–30% of their water needs from their feed ration, it would then be essential that cattle would require a daily water volume intake of 8–9% of their total bodyweight.
Weaned calves without free-choice water accessibility should be fed a minimum of 10% of their body weight in water. Lactating cows require an additional water intake of 85–90% of daily milk production in addition to the 8-9% needed for maintenance. Milk is between 12–13% dry matter solids and 87–88% water. Calves or cows subjected to heat stress or fluid loss disease will require an additional 20–30% daily of water intake for maintenance of body functions.
Clinical signs of dehydration
Severely challenged cattle can dehydrate in excess of 10% of their bodyweight. Clinical signs include: eyes sunken into orbits, skin remains tented indefinitely, dry mucus membranes, and depression is evident. This degree of dehydration is potentially life threatening and procedures of IV fluid therapy and oral rumen large volume supplementation should be initiated immediately.
Cattle with dehydration of 5–10% of their bodyweight will exhibit partial sunken eyes into the orbit, skin tenting that is 4 to 8 seconds in duration, tacky mucus membranes, and reduced dry matter intake with a corresponding decrease in productivity. University studies indicate that cattle with 7–8% percent dehydration levels have impaired immune response.
Cattle with 2–4% dehydration or less will have minimal observable clinical signs but physiological and performance efficiency can be reduced.
Clinical experience is the best way to assess the degree of dehydration encountered, the etiology causing the compromised fluid volume, and the method and amount of fluid required to restore normal hydration and vascular pressure status. Initial judgment needs to be reassessed during therapy to determine final fluid replacement needs.
Rehydration for ruminates can be accomplished in three ways: 1) parental through IV or subcutaneous administration, 2) oral rumen supplementation with large volumes or a combination of parental, and 3) oral supplementation. It is important for replacement fluids calculations to consider both maintenance requirements and compensatory fluid losses.
Pre-ruminate calves that are able to stand and are alert, if dehydrated less than an estimated 8%, can be rehydrated with subcutaneous or oral fluids. Calves less than 5 days typically are not severely acidotic and an alkalinizing solution is not mandatory. Oral fluids that are acidified with energy sources and electrolytes are commonly used. These can be fed in water or administered with an esophageal feeder. Some electrolyte solutions can be added to the milk feeding to reduce labor expense while still rehydrating the calf providing water is available free choice.
Calves that are dehydrated more than 8%, recumbent, or entering hypovolemic shock, need IV fluid therapy. Saline or Ringer's solution are recommended for this age group. Older calves will need an alkalizing agent added to therapeutic fluids to correct systemic acidosis. The use of oral or parental fluids, and the volume to correct dehydration, is based on clinical assessment of the calf.
Dehydrated adult cattle usually have a metabolic alkalosis and it is important to use non-alkalinizing fluids. Alkalosis is addressed by providing more extracellular anions relative to the excess of cations. Fluid preparations, whether oral or IV, need to contain sources of chloride electrolytes when administered to dehydrated cattle.
Oral rehydration of adult cattle is sufficient in most cases where dehydration is less than 8% of bodyweight and the animal is not toxic. Oral administration by using a full length orogastic tube (14-foot tube marked at the 10-foot length to insure rumen placement) and pumping in 20 to 50 liters of fluid depending on rumen capacity and degree of dehydration. Non-chilled water when mixed with electrolytes is the preferred fluid choice and will replace the need for intravenous isotonic fluids for all but the severely dehydrated or toxic animal.
For adult cattle dehydrated 10% or more, and compromised toxic cows, IV isotonic fluids are necessary. If hypokalemia is suspected, 20–40 mEq/L of potassium chloride should be added. Hypocalcemia is a common confounding problem in a lactating cow that is dehydrated and off feed. Adding 250–500 ml of 23% of calcium gluconate will address the issue. Adding 5% glucose per liter will supply energy. Quantities of fluid administered are dependent on the level of dehydration and degree of vascular expansion needed to maintain cell perfusion. It is common to give 40 liters of fluid by rapid IV infusion (about 12 liters per hour) to expand the fluid volume and prevent hypovolemic shock. Fluids of choice are isotonic saline, Ringer's solution, or non-pyogenic distilled water with added electrolytes, warmed closed to body temperature.
Awareness of dehydration
Not all situations of dehydration in the bovine are easy to recognize. The rumen acts as a fluid reservoir by which body fluid balance can be maintained for a short period of time. This causes "shrink" of the animal's normal body weight and, if not corrected, will lead into the stress observed as clinical dehydration.
Being aware of situations that will cause shrink presents an opportunity to be proactive and use preventative measures to insure body fluid homeostasis.
Providing accessible high quality water, anticipating increased maintenance needs from environmental heat, transportation, pyrexia associated with disease, fluid loss from diarrhea these are examples of situations that can be addressed to maintain hydration with the use of water or feed added electrolytes on a pen or herd basis.