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Identifying the four D’s of scours and how to treat it

Drew A. Vermeire for Progressive Dairyman Published on 21 May 2018
calf with bucket

On average, dairies lose 5 to 15 percent of their calves in the first three weeks of life due to scours, making it the number one killer of calves. However, it doesn’t have to be this way. With the right tools and protocols, it is possible to maintain less than a 1.5 percent death loss in these young calves.

Identifying the four D’s of scours

Calves develop scours due to infection by bacteria, viruses or protozoa. Bacteria, such as E. coli, cause scours by releasing toxins that can interfere with water being absorbed from the intestine into the blood or by causing intestinal crypt cells to increase water secretion from the blood into the intestine. Viruses, such as rotavirus and coronavirus, destroy the tips of intestinal villi, which are the site of water absorption. Protozoa, such as cryptosporidia, infect intestinal cells, disrupt their function and reduce water absorption. Improper mixing of milk replacer and some other feed issues can also cause scours.



Identifying scours early is key to survival. Below are the signs and symptoms to look for or what I like to call the “four D’s of scours”:

1. Diarrhea – Normal calves transfer about 25 gallons of water from the blood into the intestine throughout the day as part of normal digestion. A disruption in the balance of secretion and absorption of water back into the blood results in an increase in the fluid content in the intestine. The buildup of fluid in the intestine results in more liquid feces, which we see as diarrhea or scours. Regardless of the cause of diarrhea, the loss of body fluid as diarrhea leads to the second “D,” dehydration.

2. Dehydration – Normal calves drink milk and water, and typically have a net fluid gain of approximately +1,150 ml per day. Conversely, calves with scours have a net loss of -3,350 ml per day, according to research at Colorado State University. As a result of this daily water loss instead of gain, calves quickly become dehydrated.

Dehydration zones to look for are:

  • Bottle zone 1: Mildly dehydrated calves have 1 to 6 percent loss of bodyweight and usually have very few visible outward signs.
  • Bottle zone 2: Moderately dehydrated calves have 6 to 8 percent loss of bodyweight and have sunken eyes, droopy ears and skin tents for one to three seconds before returning to normal when pinched.
  • Bottle zone 3: Severely dehydrated calves have lost 8 to 11 percent of bodyweight and have deeply sunken eyes, cold feet and skin tents for four-plus seconds when pinched. Fast action is needed here or calves will reach the next phase.
  • Dead zone: When a calf has lost 12 percent of its bodyweight, the calf likely dies. Moderate and severe dehydration lead to the third D, depression.

3. Depression – The outward signs of metabolic acidosis are called depression. When fluid is stuck in the intestine and excreted instead of returning to the blood, blood volume decreases and oxygen available for tissue metabolism also decreases, resulting in a change from aerobic to anaerobic respiration. Lactic acid is then produced, which lowers blood pH, and causes calves to lose the ability to suck, stand or respond to tactile or menace stimulation. Many textbooks state that depression and dehydration are linked. However, my personal experience is that there are circumstances where calves can be severely dehydrated but not depressed, and the opposite is also often true. Metabolic acidosis ultimately is the cause of the last D, death.


4. Death – A fatal heart attack occurs when blood pH drops below a critical level. Usually, calves have lost 12 to 14 percent of bodyweight and are often comatose when death occurs. Sometimes calves that have been more than 8 percent dehydrated but have been rehydrated will die unexpectedly, so it’s important to prevent severe dehydration.

What to do about scours (1-2-3)

Treat dehydration! Regardless of the cause of diarrhea, calves die because of dehydration and the subsequent problems it causes. Continue to offer milk or milk replacer two to three times per day. If calves do not drink their milk, throw it away. Never give milk or milk replacer using an esophageal feeder.

Calves need up to three bottles of electrolytes per day, in addition to milk or milk replacer, depending on their level of dehydration. Remember 1-2-3. Start feeding one bottle per day to calves with scours; feed two bottles per day to calves with moderate dehydration; and feed three bottles per day to calves with severe dehydration. Identify calves that need extra fluids, and give electrolytes immediately after the morning feeding to calves that can’t drink milk, and every two to three hours throughout the day to keep calves hydrated. Calves that show signs of dehydration, such as sunken eyes, etc., need a bottle of electrolytes immediately. Always try bottle-feeding the electrolytes first, but if the calf refuses to drink, feed them using an esophageal feeder.

Making sense of electrolytes

Electrolytes were developed for humans in the 1960s and contained sodium bicarbonate and dextrose (Generation I). This type of product is best used for feeding midday to shipped calves after arrival. In the 1970s, the World Health Organization (WHO) replaced sodium bicarbonate with sodium citrate (Generation II) because sodium bicarbonate neutralizes stomach acid, thus interfering with protein digestion and allowing reinfection by pathogens normally killed by the acid pH of the stomach. An electrolyte that does not contain sodium bicarbonate allows for continued milk feeding and is best used for calves with dehydration.

Surviving scours table

One downside to Generation I and II electrolytes is the use of dextrose, which due to its osmotic pressure, draws water the wrong way from the blood into the intestine much like table sugar draws water out of strawberries to make juice when you make strawberry shortcake. Today, WHO has replaced dextrose with complex glucose polymers (Generation III). These polymers have low osmotic pressure and push water from the intestine back into the blood, making Generation III an ideal oral treatment for severe dehydration. In fact, with severely dehydrated calves, this treatment is preferred over intravenous fluid.


Severely dehydrated calves can be given Generation III electrolytes using an esophageal feeder instead of IV Ringer’s solution, but dextrose-containing electrolyte products have too high osmotic pressure to use for severely dehydrated calves.  end mark

Drew A. Vermeire
  • Drew A. Vermeire

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  • Nouriche Nutrition Ltd.
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PHOTO: When treating scouring or dehydrated calves, remember 1-2-3: one bottle for scours, two bottles for moderate dehydration and three bottles for severe dehydration with appropriate products. Doing this keeps more calves alive. Staff photo.