Treating Scour in Calves
Scour is the most common disease in young calves and, as a result, is the greatest single cause of death in calves, accounting for almost 50% of all calf deaths in the UK1. One in seven dairy breed calves and one in thirteen beef breed calves are believed to die as a result of scour during the rearing phase in the UK each year1. Scouring calves have a major impact on the economic viability of farms, with economic losses due to treatment costs, labour costs and calf mortality. The Scottish Agricultural College (SAC) estimate an average cost of £44 per calf, excluding the cost of calf mortality.
Figure 1. Main causes of scour in neonatal calves in the UK (VIDA 2012)
All of these pathogens can be found in faecal samples from perfectly healthy calves but poor environmental and management practices can predispose animals to the development of disease:
Presence of pathogens in scour does not always equate with disease:
Increased secretion of electrolytes and bicarbonate from gut cells proximally in the small intestine. Water follows into the gut lumen. This hypersecretion overwhelms the absorptive capacity of the colon, and diarrhoea results. This pathological mechanism is caused by E. coli. Enterotoxinogenic serotypes bind to specific receptors in the small intestine causing increased sodium, chloride and bicarbonate secretion in to the lumen. This results in rapid dehydration. The receptors in the small intestine are only present for the first few days of life, hence E. coli diarrhea is only usually seen in very young calves.
Pathogens such as Rotavirus, Coronavirus and Cryptosporidia cause intestinal villous atrophy, reducing the small intestine’s ability to absorb nutrients. There is also loss of surface enzymes and transport mechanisms. This results in the presence of undigested lactose in the colon, which ferments. Fluid and electrolytes are drawn into the colon.
Causes can include rapidly changing milk replacer brand, changing from waste milk to milk replacer, and stressors such as transport, weather, vaccinations, dehorning, etc. This results in a failure of adequate milk digestion in abomasum. It is the end result of an oversupply of undigested milk nutrients in the intestines which overwhelms their absorptive capacity. Pathogens use the extra nutrients to multiply which can predispose to pathogenic scour.
No matter which is the inciting pathogenesis, the result is diarrhoea, dehydration, weakness, acidosis and electrolyte imbalance which can eventually lead to shock, coma and possibly death.
Oral rehydration therapy
For neonatal calf diarrhoea, oral rehydration therapy is the single most important therapeutic measure and is usually successful if instigated immediately after diarrhoea has developed.
The main functions of oral electrolytes are to address the following consequences of scour:
When should you treat with electrolytes?
Calves can lose 5 to 10% of their bodyweight as water within the first day of scouring. Fluid loss in excess of 8% requires intra-venous fluid therapy, and over 10% loss can result in death. This makes daily calf monitoring and quick treatment essential. The amount of water lost by scouring calves can be estimated by skin tenting, gum condition, attitude, and ability to stand or suckle (Table 1).
Table 1. Clinical symptoms that help evaluate amount of dehydration in calves.
Adapted from: Can Vet J. (1989); 30(7): 577–580. A retrospective study of the relationship between clinical signs and severity of acidosis in diarrheic calves. Jonathan M Naylor.
Fluid deficit = % of dehydration X body weight
This deficit needs to be administered in addition to fluids necessary for maintenance requirements (50ml/kg/day). As a general rule of thumb, ongoing losses in diarrhoea are estimated between 1 to 4l/day depending on faecal consistency.
The calf’s gastro-intestinal tract must be at least partly functional to be able to administer oral fluids safely. If the calf has ileus, fluids pool in the forestomach, which can lead to bloat and rumenal acidosis. Calves with any sort of suckle reflex/chewing action can safely tolerate oral fluids.
Anorexic, depressed, dehydrated, recumbent, bradycardic calves require intravenous fluid therapy.
What should the oral rehydration solution contain?
The main components to consider when selecting the correct formula are: