Diarrhoea is a commonly reported disease in newborn calves, lambs and kids. It has a major impact on the economic viability of livestock operations, due to the direct costs of animal losses and treatment and the long-term effects on performance.
Diarrhoea is defined as an increase in faecal water loss due to an imbalance between the absorption and secretion of water and electrolytes. The diarrhoea in ruminants is a complex, multi-factorial disease resulting from interactions between host, environment, nutrition and infectious agents.
Gastrointestinal disorders can be caused by pathogens, for example viruses, bacteria and protozoa, and non-infectious factors such as feeding, housing conditions, and management practices.
Diarrhoea is the most observed clinical sign of illness in young ruminants, and the number one cause of mortality before the age of one month. Once diarrhoea has developed, appropriate management is crucial to avoid further economic losses, minimise any negative impact on animal welfare and reduce farmer distress.
The pathophysiology of diarrhoea includes increased intestinal secretion and decreased intestinal absorption of fluids along with increased passage of intestinal contents.
The highest priority in treating scours is to replace the water and electrolytes lost via fluid therapy. Metabolic acidosis is a frequent and potentially severe complication of neonatal ruminant diarrhoea.
Faecal fluid loss in calves with severe watery diarrhoea can reach 20% of body weight per day. One of the most important factors in decreasing mortality associated with diarrhoea in calves is the proper use of oral and intravenous fluid therapy.
Oral rehydration therapy, originally developed in human medicine, rapidly became the cornerstone of programs for the control of diarrhoeal diseases. It is the single most important therapeutic measure to be carried out by the farmer, and is usually successful if instigated immediately after diarrhoea has developed.
To be efficient, an oral rehydration solution must satisfy the following requirements:
- supply sufficient sodium
- provide agents that facilitate absorption of sodium and water from the intestine
- provide an alkalising agent that corrects the metabolic acidosis
- provide energy
Sodium is the principle determinant of the extracellular fluid volume; it must be present in adequate concentrations in an oral electrolyte solution (ORS) to rapidly correct the losses. Current knowledge indicates that ideal concentrations should be:
- Sodium - between 90 and 130 mmol/L
- Potassium - between 10 and 20 mmol/L
- Chloride - between 40 and 80 mmol/L
Glucose, neutral amino acids (e.g. glycine or glutamine) and volatile fatty acids (e.g., acetate or propionate) have been shown to enhance sodium absorption in the intestines.
Newborn ruminants are more prone to developing severe metabolic acidosis during periods of diarrhoea. This is why the recommendation on the alkanising capacity for the ORS is high; 60 to 80 mmol/L.
When considering the importance of strong ion difference (SID) in correcting metabolic acidosis, the administration of an oral electrolyte with a high SID (79-93 meq/L) is more effective. The SID can be calculated using this formula:
[Na+] + [K+] - [Cl-] = SID
Oral rehydration should be considered as a supplement to usual (milk or milk replacer) intake, initiated at the onset of symptoms with the main objectives of restoring ionic balance and countering acidosis.
Electrolyte solutions only partially cover the calf's energy requirements. To limit the negative energy balance, to maintain the gut's ability to digest milk and to facilitate the return to milk feeding, the ORS should be given for as short a period of time as possible, be as energy-rich as possible, and contain lactose rather than glucose in order to maintain intestinal lactases.
References are available on request