At the February 2020 Northeast Ohio Dairy Conference organized by the Killbuck Valley Veterinary Association, Jess Goff, a veterinarian and professor emeritus of teaching and research at the Iowa State University veterinary college, gave an excellent presentation on calf scours/diarrhea that I will attempt to summarize in this column. Understanding calf diarrhea begins with knowledge about the normal functioning of the calf small intestine and how diarrhea disrupts that function.
The small intestine functions to allow the absorption of water, electrolytes, simple sugars, amino acids, proteins and short chain fatty acids that occur as milk proteins and lactose are digested. The absorption capacity of the gut is dependent upon healthy functioning villi and micro-villi, which are finger like projections that greatly increase the surface area of the gut. There are proteins between cells of the villi that serve as a barrier to keep harmful bacteria out. Dietary electrolytes, starch, sugars, amino acids, and even water itself all need transporter mechanisms at the cell surfaces and within the cell to get these nutritional components into the bloodstream and move them to where they are needed in the body.
Dr. Goff said that there are three main causes that explain how small intestine function is disrupted by diarrhea. Those causes are secretory, malabsorptive and osmotic diarrhea. Regardless of the cause, the danger of any diarrhea is dehydration. Excessive dehydration is what kills calves. Understanding the causes of diarrhea helps to understand prevention and treatment protocols. Secretory diarrhea involves excessive secretion or a severe watery diarrhea. It is the result of a toxin that triggers an excessive flushing reaction of the small intestine. For example, some strains of E. coli secrete a toxin that binds to the small intestine in widespread areas. That toxin activates a mechanism that cause hypersecretion of sodium (Na) and chlorine (Cl) that can deplete body stores.
Malabsorptive diarrhea is caused by pathogens or toxins that weaken and kill the gut lining and cells along the villi, those finger-like projections so important to nutrient absorption. These pathogens also destroy the villi-associated proteins that act as a barrier to keep bacteria out. According to a University of Minnesota publication, 95% of this type of infectious calf scours is caused by rotavirus, coronavirus or cryptosporidium organisms. Cryptosporidiosis and coccidiosis are both parasitic malabsorptive diarrheas. Two other important points with this type of diarrhea: first, the causal organisms are not bacteria, so antibiotics are not useful. Second, some of these pathogens can invade blood vessels and cause bloody diarrhea.
Osmotic diarrhea is triggered by inadequate absorption of nutrients as a result of overfeeding of excessive feeding of ingredients that are hard to digest or that are not absorbed well. This type of diarrhea can be made worse if the secretory or malabsorptive diarrhea causal organisms are present as well. According to Dr. Goff, osmotic diarrhea is often seen during cold weather when calves need more nutrients and instead of adding additional feedings of milk replacer, the calf is simply feed more milk replacer but still only twice per day. The better solution is increasing the number of feedings per day.
Treatment of diarrhea in calves is centered around the fact diarrhea kills calves by dehydration. Physiologically the calf is in a condition of acidosis with high blood potassium. Physically the calf begins to lose the suckle reflex, body temperature falls, eyes become sunken and skin, when tented is slow to return to normal position. Tenting of the skin and timing return to normal is correlated with percent dehydration and the need for rehydration fluids.
Tenting involves pinching up the skin in the neck area of the calf and releasing. In a healthy hydrated calf, the skin returns to a normal flat position within 2 seconds. If the delay to return to normal is 3-5 seconds this indicates the calf is 6-7% dehydrated, an 8-10 second delay indicates an 8-10% dehydration level, and if the calf is unable to stand and the skin is not flattening when tented this is a dehydration level of 10-12% or greater. Death usually occurs at dehydration levels between 13-14%. Oral rehydration fluids should be administered anytime dehydration is outside of normal, even with mild diarrhea. Once a level of 10% dehydration occurs, rehydration fluids need to be provided intravenously.
The essential component of all rehydration fluids is water. In addition, the rehydration solution should contain alkalinizing agents to decrease the acidosis the calf is experiencing. These usually involve sodium and include bicarbonate and possibly lactate, acetate or propionate. Other components are glycine, glucose and electrolytes such as potassium and chloride. While treating for diarrhea, the calf needs to continue to receive milk or milk replacer in addition to the rehydration fluids. The milk or milk replacer is needed for energy. The most effective therapy is when the milk and the oral electrolytes are fed several hours apart. Feed calves with diarrhea in smaller amounts but more frequently. Do not add the electrolytes to the milk or milk replacer, this will create a situation of osmotic diarrhea.
Rory Lewandowski is an OSU Extension Agriculture & Natural Resources Educator and may be reached at 330-264-8722.
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