Exploring the Origins of Scours in Dairy Calves – Dr. Noah Litherland, Vita Plus

By Dr. Noah Litherland, Vita Plus dairy youngstock technical specialist
Determining the cause of scours in calves is often difficult.  Unlike the majority of monogastric animals, ruminants cannot vomit to expel stomach contents before reaching the small intestine.  Newborn calves also make low amount of stomach acid (to protect colostral antibodies), which is a natural inhibitor of viable bacteria entering the small intestine.

Calf scours can be defined as the discharge of more fluid than normal, increased frequency of discharge, and greater loss of water and important electrolytes than is taken in.  Normally, considerably more fluid is secreted into and out of the intestine and absorbed than is ingested by the calf.  If the normal cycling of body water into and out of the intestinal tract is disrupted, a resulting disturbance of the cycle and risk of dehydration and loss of important electrolytes (salts) can occur.

Two pathways of intestinal fluid disruption can occur during scours:

1.  Excessive secretion of water into the intestine coupled with normal water reabsorption back out of the intestine
2. Normal water secretion into the intestine, but reduced water absorption back into the intestine

The net result of scours is an imbalance of normal body fluids.  Dehydration can be evaluated by skin “tents,” a mouth that isn’t slick, limbs and ears are cold, eyes sink and a gap appears between the eyeball and inner lid, urine output drops, and a depression in the attitude of the calf is observed.  To evaluate skin tenting, twist a large fold of loose skin in the neck area.  A skin “tent” for four seconds or greater indicates moderate dehydration and a need for intervention.

Perhaps one origin of calf scours starts with an upset in the osmolarity of the intestinal contents.  An example would be feeding too great of a concentration of milk solids (not mixing calf milk replacer and water to achieve a total solids ranging from 12.5 to 15 percent).  The higher concentration of milk solids pulls water (through osmotic pressure) from blood and cells into the small intestine.  This increased water in the gastrointestinal tract speeds the rate of passage of nutrients through the gastrointestinal tract.

A concurrent disruption in nutrient absorption through the lining of the small intestine occurs as well as a disruption of the normal bacterial flora in the gut.  These normal and beneficial bacteria have developed a mutually beneficial symbiotic relationship with the calf intestine and serve to defend the intestine through protection against pathogenic bacteria such as E coli. and salmonella.  E. coli have the ability to attach to the intestinal lining, set up shop and reproduce.  Irritation of the intestinal lining results in the damage of the enterocytes, which are the cells in the intestine responsible for absorption of nutrients.  Once pathogenic bacteria become prevalent in the gastrointestinal tract, they can proliferate in numbers and also increase in their pathogenicity.  Further damage of the small intestinal lining reduces the physical barrier that prevents intestinal contents from directly entering the blood stream.

How do calves pick up bacterial infections?  Flies, insects, birds, and vermin commonly spread E. coli from animal to animal and can be spread from calf to calf via direct contact.  Fecal-oral contact is the means of infection.  Maintaining high-level sanitation in the calf environment is critical to minimizing calf exposure to pathogens.  Start by developing an equipment sanitation protocol for all feeding equipment, including the colostrum harvesting.  Provide disposable gloves for all calf workers.

The most important take-home message is to detect the scouring calf before fluid loss becomes severe so oral replacement of fluids is still effective.  It is important to replace lost body fluids in large enough quantity and often enough so that losses do not become profound.

Three times daily feeding of warm electrolytes mixed according to label instructions as well as intravenous or subcutaneous infusion of lactated ringers solution are both excellent strategies to minimize the impact of dehydration caused by scours.  Try delivering electrolytes via a nipple bottle or esophageal tube if calves refuse to drink from a pail.  The most common mistakes are to give too little supplemental fluid in a timely manner and discontinuing feeding milk.  One of the signs that enough fluids are being replaced is that normal volume of urination resumes.

Prevention of calf scours starts with timely feeding adequate amounts of clean colostrum, consistently mixing milk replacer at 12.5 to 15 percent total solids, maintaining good equipment hygiene, and rapidly identifying and rehydrating calves that develop scours.