Diarrheal diseases continue to be one of the most common health problems for calves, causing serious welfare problems. One third of calves in a production run develop some degree of scours in their first few weeks of life. The financial losses resulting from scours are considerable, including costs for treatment, negative weight gain and death. In addition, much work is invested in the special care of sick calves.

Scours can be defined as increased loss of water through feces. As with all complex, multifactorial clinical conditions, the incidence and course of the disease depends on the interactions between calves, the environment, nutrition and any infectious agents.

Pathophysiology of scours in calves

The causes of diarrhea can be classified as either infectious or non-infectious.

Within the environmental influence, deficiencies in the improper administration of milk and inadequate housing conditions are the most important non-infectious causes of diarrhea. Although with excellent animal management systems, enteropathogenic organisms can infect calves because of their immature immune systems and limited energy and nutrient reserves.

Neonatal calves are highly susceptible to infectious diarrhea. Viruses such as rotavirus and coronavirus, in addition to bacteria are the most important pathogens. Parasites Cryptosporidium spp. and coccidia are also frequent causes of scours in calves.

Because of their young age, calves that show signs of scours are prone to infectious disease. Specific pathogens commonly cause disease in calves at different ages.

Clinical signs

Regardless of the ethology and pathogenesis, scouring calves lose large amounts of fluids, electrolytes and buffering agents, causing severe health problems.

The consequences of scours of greater clinical concern are:

• Dehydration:

A 7% loss of extracellular fluid volume leads to clinical signs and a 30% loss is fatal.

• Acidosis:

Metabolic acidosis is the lowering of the blood pH. Several factors contribute to the development of acidosis: the primary cause is the loss of buffering agents, especially bicarbonate. Additionally, dehydration causes decreased renal perfusion, which in turn leads to decreased renal excretion of hydrogen ions.

Finally, lactic acidosis may occur from increased lactate production due to anaerobic metabolism followed by reduced tissue perfusion.

An acidosis has an adverse effect on several metabolic processes, affecting enzymatic activity and exchange of hydrogen and potassium, resulting in hyperkalemia and, in turn, heart failure, and in severe cases death.

• Decrease in electrolytes:

Because electrolyte balance is essential for many important biochemical processes, a decrease in electrolytes results in a severe metabolic imbalance.

The most important electrolytes are the positively charged cations of sodium, magnesium and potassium as well as the negatively charged anions such as bicarbonate and chlorine. In case of diarrhea, the excretion of electrolytes can be increased by more than 30 times compared to normal.

• Energy deficit:

Because of their high metabolic rate and rapid growth rate, newborns need high-energy feeds. In case of scours in calves, reduced nutrient intake (anorexia), high energy requirements and poor absorption and digestion quickly lead to a negative energy balance.

Treatment of scours in calves

There are two general principles of therapy for diarrhea: treat the cause and treat the signs. For non-infectious causes, the most important thing is the elimination of any negative environmental influences. In the case of infectious scours, the causative pathogen must be eliminated; to combat viral scours, vaccination of cows can protect calves by conferring passive immunity.

E. coli infection can be treated with antibiotics and Eimeria spp. infection can be treated with toltrazuril. However, the use of antibiotics to treat moderate clinical scours may not be appropriate; the calf’s immune system can deal with a pathogen within a few days of infection and its intestinal epithelium shows good regeneration capacity with new cells sufficiently resistant to reinfection.

As natural alternatives to the use of antibiotics, natural microbicides ca be used as they do not generate resistances and help to reduce the use of chemical additives and antibiotics in animal feed. In the case of protozoal infestations, the use of intestinal conditioner pronutrients is effective as a prevention method.

The key therapeutic considerations when treating diarrhea are, therefore, to promote rehydration, correct acidosis, replace electrolytes and reserve or avoid an energy deficit.

If dehydration is less than 8% of the calf’s weight, fluid therapy with oral rehydration solution is the treatment of choice. Parenteral fluid therapy is necessary when dehydration is less than 8%, when the calf refuses to drink, when acidosis is severe, when the overall condition worsens rapidly or when the animal has advanced malabsorption syndrome. Parenteral rehydration is also indicated in cases of failure of appropriate oral therapy.

Depending on the severity of diarrhea and degree of dehydration, a dehydrated calf needs up to 12 liters per day of oral rehydration. With fluid administration, absorption is only partial (60 – 80%). It is important to note that the fecal volume may increase during oral rehydration, but this does not indicate a failure of treatment.

The optimal composition of the oral rehydration solution should consider the needs of the animal in terms of rehydration, buffering, electrolyte replenishment and correction of energy deficit.

Several important rules should be followed during the administration of oral rehydration solution therapy:

• Start therapy immediately at the first clinical sign.
• Do not discontinue milk administration.
• Provide water ad libitum.
• Never dilute milk with bicarbonate-based rehydration solution.
• Choose a palatable oral rehydration solution.
• Do not stop therapy early.
• Calves with this problem are lactating; they must be kept warm, provided with a dry, clean bed and require patience to be encouraged to drink.