The principles of therapy are relatively simple; the physical, logistical, and economic constraints can be (and are) overcome
by creative, resourceful practitioners. Administration of effective and economical fluid and electrolyte replacement therapy
is achievable by every large animal practitioner.
The most frequent indication for fluid therapy for calves is neonatal calf diarrhea. Regardless of the etiologic organism,
the metabolic changes resulting from diarrhea in calves are similar. They include (1) dehydration, (2) acidosis, (3) electrolyte
abnormalities, and (4) negative energy balance and/or hypoglycemia. The major cause of dehydration of these calves is fecal
fluid loss, which can be as much as 13 per cent of body weight in 24 hours. Compounding this problem is decreased intake from
either anorexia or withdrawal of milk by the owner. Acidosis results from bicarbonate and strong cation loss in the stool,
lactic acid accumulation in tissues, decreased renal excretion of acid, and increased production of organic acid in the colon
in malabsorptive diarrheas. Along with water and bicarbonate, Na, Cl, and K are lost in the feces, which results in a total
body deficit of these ions. Negative energy balance can occur in diarrheic calves owing to decreased milk intake, decreased
digestion or absorption of nutrients, or replacement of milk with low-energy oral rehydration solutions. Increased energy
demand, such as that resulting from cold weather or fever, exacerbates these problems.
The range for PCV in healthy neonatal calves is 22 to 43 per cent, much too variable to provide reliable quantitative information
of hydration status, at least with a single sampling. The TPP is even more variable, depending greatly on the degree of colostral
immunoglobulin absorption that occurred, as well as hydration. Without a reliable quantitative measure for hydration status,
we must rely on estimates based on clinical signs. Table -1 provides a guideline for estimating the degree of dehydration
in cattle. This table is based on research conducted by Constable et al,1 and is the most critically validated estimate of dehydration in calves. However, even in the absence of a validated system
of estimating degree of dehydration, rehydration has been clinically successful, suggesting that precise estimates are not
necessary. Rather than becoming overly concerned with pinpointing the exact degree of dehydration, veterinarians should be
concerned whether intravenous therapy is needed, or whether voluntary or forced oral supplementation will suffice. Rather
than defining an exact long-term fixed plan for rehydration, we should begin with a reasonable plan and adjust it as needed.
In other words, guess and reassess.
Table 1: Guide to estimation of fluid replacement requirement
Data from Constable PD et al: Use of hypertonic saline-dextran solution to resuscitate hypovolemic calves with diarrhea. Am
J Vet Res 57: 97-104, 1996
Empirically, 8 per cent dehydration is the severity beyond which it is considered that oral fluid therapy will not suffice.
According to the table above, 8% dehydration is characterized by eyeball recession of 4 mm in the skin tent duration of 6
seconds. Other clinical signs associated with severe dehydration include dry mucous membranes, and moderate to severe depression.
Calves displaying these signs will benefit the most from intravenous therapy. In general, calves that readily suckle quantities
of rehydration solution sufficient to meet their replacement, maintenance, and ongoing loss needs will respond to oral solutions.
Many of the more severely dehydrated calves will respond to forced oral solutions as well, but intravenous replacement is