More Than Just Water.
Oral Rehydration in Calves.
Approximately 25–40% of the estimated 264 million calves born each year will be replacements for dairy cows that are removed from the herd. The current crop of female calves will become tomorrow’s herd. The stakes cannot be higher for the outlook of the dairy farm—rearing healthy, productive cows are crucial to future success. However, the path to healthy calves is paved with obstacles ranging from failure of passive transfer to a multitude of infectious diseases.
Today, as throughout history, diarrhea poses a major threat to the health of a calf in the first weeks of life. A study of on-farm mortality in the UK showed that between 2011 and 2018, 25% of all deaths occurred in cattle under 3 months of age [1]. In fact, diarrhea in calves is the most economically significant disease on a dairy farm. In a 2020 survey, 81% of UK farmers had seen diarrhea in calves during the previous 12 months and 50% had lost animals to the disease over the same period. Another UK-based study has shown that diarrhea is the main cause of mortality in calves younger than two months [2].
Many causes—one result.
Diarrhea in calves is not a single disease. Rather, it is a manifestation of the many infectious and non-infectious causes associated with it. From the moment of calving, a newborn calf is exposed to numerous pathogens—bacteria, viruses, parasites, protozoa—all of which harm the intestinal tract and cause diarrhea. The most common bacteria responsible for diarrhea are E. coli, Salmonella, and Clostridium perfringens; viral and protozoal causes include rotavirus, coronavirus, bovine viral diarrhea virus, cryptosporidium, and coccidia.
Non-infectious causes of calf diarrhea include inadequate nutrition, unsanitary pens, overcrowding, and inadequate colostrum intake. Colostrum intake is crucial for passive immunity and the development of a functioning immune system. Lack of colostrum feeding increases the risk of various infections and causes a higher sensitivity to environmental pathogens. Ensuring sufficient colostrum intake is vital for future health. A calf should drink at least 3–4 liters of good-quality colostrum within the first four hours of life.
Although there are several forms of diarrhea, the secretory and osmotic forms are common among calves, and because of the numerous causes, a calf may often have both forms simultaneously. Secretory diarrhea involves toxins binding to intestinal cells, which allows fluid to move into the intestinal lumen. A common cause of this type of diarrhea is E. coli. Osmotic diarrhea results from a disruption of intestinal structures leading to unabsorbed nutrients, thereby creating an osmotic gradient, pulling fluid into the lumen.
Regardless of the form and the cause, the clinical signs of diarrhea are similar. Most noted is a decreased appetite and fluid intake, fever (usually over 40°C), and a weak appearance with sunken eyes. A severe case may present lying down with a low body temperature (cold to the touch). The fecal consistency may appear differently depending on the severity, alternating between greasy and fluid. Affected calves also show an increased frequency of defecation.
Metabolic acidosis—the next phase.
In calves, metabolic acidosis is a common result of diarrhea-induced dehydration. Without treatment, metabolic acidosis is a prime factor in the death of many of these calves. Early and intensive oral electrolyte therapy at the onset of diarrhea in calves is critical to replenish fluids and correct metabolic acidosis. Therapy should be started as soon as possible regardless of whether evidence of dehydration is seen. The clinical signs of dehydration are not obvious until the calf has lost at least 6% of its body weight in fluid (figure 1). The course of therapy depends on the severity of symptoms. Calves still able to stand and suckle can often be treated with oral rehydration solutions alone to avoid continued fluid losses and restore extracellular cell fluid volume. If there are signs of systemic illness, a veterinarian should be consulted for additional therapies such as anti-inflammatories or intravenous fluids.
Keep calves eating!
Calves must eat. A sufficient energy intake is essential to maintain the calf’s defense against infections while continuing to grow and develop. Calves have large energy requirements and little energy reserves. Since electrolyte solutions do not meet calf energy requirements; milk should not be withheld. Although feeding milk may increase fecal volume, it also provides a critical energy supply and may promote gut healing. Additionally, free access to drinking water should be provided.
Rehydration solutions are not all the same.
“They are all the same to me!” This is a common thought among farmers when thinking about rehydration solutions for calves. With so many products available, it can be difficult to choose. However, selecting an oral rehydration solution is important. It should be effective and easily added to the daily milk ration. It should also meet the goals of oral rehydration therapy, such as the correction of dehydration through normalization of the extracellular fluid volume, provision of additional energy, supply of a buffer to prevent or correct metabolic acidosis and increase sodium and water absorption from the intestines.
The alkalizing ability of an oral rehydration solution is dependent on the alkalizing agent. Alkalizing agents, more commonly known as buffering agents, are used to counteract acidosis. Oral electrolyte solutions have traditionally contained sodium bicarbonate because it has been shown to be highly effective. However, bicarbonate has several disadvantages. High concentrations of bicarbonate alkalize the abomasum, which interferes with abomasal milk clotting. The use of bicarbonate in rehydrating solutions could lead to a higher number of coliform bacteria that reach the small intestine, thus increasing the severity, duration, and mortality risk.
Other commonly used alkalizing agents include acetate and propionate—both with a similar alkalizing ability to bicarbonate. However, these agents offer additional benefits that bicarbonate does not. Unlike bicarbonate, acetate and propionate exert their alkalizing effects after they are absorbed and metabolized. These alkalizing agents help facilitate sodium and water absorption, produce energy when metabolized, and do not alkalinize the abomasum or interfere with milk clotting (figure 2). The administration of oral rehydration solutions containing acetate or propionate in milk or milk replacer have shown to be beneficial. Calves that have been fed with milk recover quicker and perform better than those that are taken off milk.
Combating the negative impact of diarrhea.
A large amount of sodium and potassium are lost when a calf has diarrhea. This can result in a lowering of blood pH (metabolic acidosis), which cannot be corrected without intervention. An oral rehydration solution must be capable of efficiently buffering (counteracting) the low blood pH. The efficiency of the buffering capacity of an oral rehydration solution is defined by the strong ion difference (SID value). For moderate acidosis, oral rehydration solutions with a high SID formulation can help—an effective oral rehydrating solution should have a SID value between 60 and 80.
Calves with diarrhea not only have a reduced ability to absorb nutrients. They also have an increased demand for energy for immune function and intestinal epithelium repair. Increasing sodium absorption is one of the functions of an oral rehydration solution and cannot be achieved without an energy source. Therefore, oral rehydration solutions should provide an energy source—often in the form of sucrose or glucose.
Formulated with sodium propionate, betaine, zinc, and glucose, Prolyt Pack® Extra meets all the requirements of an effective oral rehydrating solution. Prolyt Pack® Extra has a SID value of 79—a highly effective buffer. The propionate in Prolyt Pack® Extra serves several functions. As an alkalizing agent, propionate does not alter the pH in the abomasum, which means there is no interference with milk clotting. Propionate also enhances sodium absorption in the small intestine and can be a source of energy for the calf.
Betaine is included in the formula to function as an osmolyte to improve cellular hydration. When betaine is taken up by the cells, they can maintain water volume without having to increase ion levels thus reducing ion pump use during hyperosmotic stress. The result is that less energy is needed to maintain the osmotic balance. Prolyt Pack® Extra also contains organically bound zinc to regenerate damaged intestinal epithelium and improve intestinal barrier function, helping the calf quickly return to performance levels.
Prolyt Pack® Extra is easily added to the milk or milk replacer—act early to restore your calf's water balance!
