PATHOLOGY - Calf Scour Flashcards
What are the main risk factors for calf scour?
The main risk factors for calf scour are poor management and animal husbandry
What are the main things that can be done to prevent calf scour?
Boost calf immunity and resistance to disease
Minimise infection pressure
What can be done to boost calf immunity and resistance to disease?
Colostrum management
What can be done to minimise infectious pressure?
Housing management
Hygiene management
Stocking density
Manage sick calves
Which housing management practices can be used to prevent calf scour?
- Dry and draught free housing with good drainage and ventilation
- Calf housing should be at least 20 metres from the milking shed as adult cows can be a source of infection
- Within calving pens, calves should be no more than 5 days older than one another, as older calves can act as a source of infection for the younger calves
- Calves should be moved around the shed as little as possible
- House bobbies (male calves) seperately from the female calves
- Two metre high, solid partitions between the calf pens
Why should bobbies (male calves) be housed separately from the female calves?
Bobbies (male calves) should be housed separately from female calves as their management is often different and they may receive less colostrum than the females as they are not priositised as much as the heifer replacement calves (which will be worth more economically). Thus, the males will be at an increased risk of disease and can be a source of infection
Which hygiene management practices can be used to prevent scour?
Clean dry bedding
Regularly refresh bedding during calving season
Replace bedding completely between calving seasons
Which stocking density practices can be used to prevent scour?
Minimum of 1.5m^2 per calf (aim for min of 2 - 3m^2)
No more than 100 calves per shed
No more than 20 calves per pen
How should you manage sick calves to reduce the spread of calf scour?
Quarantine bought in animals
Remove sick calves prompty from the healthy calves
Biosecurity
Feed sick calves last and with seperate feeders of possible
What are the three pathophysiological mechanisms of calf scour?
Secretory diarrhoea
Osmotic diarrhoea
Malabsorptive diarrhoea
Describe briefly the pathophysiology of secretory diarrhoea
Secretory diarrhoea is when fluid secretion from the intestine exceeds absorptive capacity. Bacteria can release endotoxins which ultimately result in reduced sodium absorption by the villous cells and increased chloride secretion by the crypt cells
Describe briefly the pathophysiology of osmotic diarrhoea
Osmotic diarrhoea is when substances within the intestinal lumen exert osmostic pressure, drawing fluid into the lumen. This can be caused by sodium and chloride within the lumen, but also unabsorbed molecules of a dietary origin
Describe briefly the pathophysiology of malabsorptive diarrhoea
Malabsorptive diarrhoea can be caused by passive malabsorption of fluid from the intestinal lumen due to villous atrophy and morphological changes to the absorptive surface of the intestine. Crypt hyperplasia can also occur and immature secretory cells can migrate onto the villi and increase secretory capacity, contributing to the diarrhoea
What are the two main classifications of calf scour?
Nutritional scour
Infectious scour
What are some of the potential causes of nutritional scour in calves?
Excess volumes of milk
Feeding at the wrong temperatures or concentrations
Irregular feeding times
Which bacteria can cause calf scour?
E. coli
Salmonella
Campylobacter
Describe the morphological characteristics of E. coli
E. coli is a Gram negative, facultatively anaerobic, rod bacteria
What is the pathogenesis of enterotoxic E. coli (ETEC)?
Enterotoxic E. coli (ETEC) adheres to the microvilli on the intestinal epithelium via the K99 antigen which allows the bacteria to bind to the intestinal epithelium, and produce heat labule and heat stable toxins. Heat labile toxins stimulate Cl- secretion from the enterocytes. Heat stable toxins inhibit the Na+/Cl- co-transporters on the surface enterocytes and stimulate Cl- and water secretion from the crypt enterocytes, resulting in secretory and osmotic diarrhoea
What is the typical signalement for enterotoxic E.coli (ETEC) mediated scour?
Enterotoxic E. coli (ETEC) causes scour in calves less than 5 days old
What are the clinical signs of enterotoxic E.coli (ETEC) mediated scour?
Profuse, four smelling scour
Wet mouth
Abdominal distension
± Blood in the scour
± Pyrexia
± Systemic clinical signs
Which strains of E. coli cause scour in older calves?
Enteropathogenic E. coli (EPEC)
Enterohaemorrhagic E. coli (EHEC)
What is the pathogenesis of enteropathogenic E. coli (EPEC)?
Enteropathogenic E. coli (EPEC) adheres to and translocates into the enterocytes, resulting in damage to and loss of the microvilli, compromising the absorptive capacity of the enterocytes resulting in malabsorptive diarrhoea
What is the pathogenesis of enterohaemorrhagic E. coli (EHEC)?
Enterohaemorrhagic E. coli (EHEC) produces Stx1 and Stx2 of shiga toxin (verotoxin) which causes inhibition of protein synthesis and enterocyte apoptosis, compromising the absorptive capacity of the intestinal epithelium, resulting in absorptive diarrhoea
Which species of salmonella most commonly cause calf scour?
Salmonella typhimurium
Salmonella dublin
What is the pathogenesis of salmonella?
Salmonella adheres to and invades the intestinal epithelial cells mediated by fimbriae. Salmonella preferentially adheres to and invades M-cells, however invasion via enterocytes also occurs. Within the intestinal epithelium, endocytosis occurs which forms vacuoles which translocate the salmonella to the lamina propria macrophages. Salmonella neutralise the nitric oxide within the macrophages and then reside within the phagylolysosomes. Salmonella toxins trigger acute inflammation of the gastrointestinal tract, as well as cause enterocyte damage and interference of closure of Cl- channels resulting in secretory diarrhoea. Salmonella toxins can also cause vascular thrombosis. The macrophages transport the salmonella to the mesenteric lymph nodes and then to the liver via the hepatic portal system
What is the typical signalement for salmonella mediated scour?
Salmonella causes scour in calves of any age, but mainly calves less than 2 months old
What are the clinical signs of salmonella mediated scour?
Scour
Pyrexia
± Blood in the scour
Which viruses can cause calf scour?
Rotavirus
Coronavirus
What is the pathogenesis of rotavirus?
Rotavirus invades and replicates within the enterocytes, followed by destroying the enterocytes resulting in secretory and malabsorptive diarrhoea
Which signalement is typically affected by rotavirus mediated scour?
Rotavirus typically causes scour in calves between 5 to 21 days old
What are the clinical signs of rotavirus mediated scour?
White scour
Dehydration
(T/F) Coronavirus mediated scour is very similar to rotavirus mediated scour
TRUE.
Which parasites can cause calf scour?
Cryptosporidium parvum
Coccidiosis
Helminths
What is the pathogenesis for cryptosporidium parvum?
Cryptosporidium parvum cause invagination of the intestinal luminal membrane ans cause villous atrophy, crypt hyperplasia and enterocyte apoptosis, resulting in malabsorptive and osmotic diarrhoea
What is the typical signalement for cryptosporidium parvum mediated scour?
Cryptosporidium parvum typically causes scour in calves between 1 week and 3 months old
What are the clinical signs of cryptosporidium parvum mediated scour?
Scour
Dehydration
Why is cryptosporidium parvum so challenging to remove from the enviornment?
Cryptosporidium parvum oocysts persist in the enviornment and are very challenging to kill
What is required to kill cryptosporidium parvum oocysts in the environment?
Ammonia-based disinfectants
What is the pathogenesis for coccidiosis?
Coccidia cause enterocyte rupture resulting in malabsorptive and osmotic diarrhoea
What is the typical signalement for coccidia mediated scour?
Coccidia mediated scour typically affects calves between 3 weeks to 3 months old
What are the clinical signs of coccidia mediated scour?
Black/bloody scour
Abdominal pain
Faecal tenesmus
What is necrotic enteritis?
Necrotic enteritis is condition of unknown aetiology which affects 7 to 9 week old beef calves, usually when they have been put out to grass
What are the clinical signs of necrotic enteritis?
Pyrexia
Bloody scour
Anaemia
How do you diagnose the cause of calf scour?
Collect faecal samples from at least six of the sick calves and conduct faecal analysis, focusing on all of the major pathogens relevant to that age group. Additionally, taking faecal samples from healthy cows can provide a baseline for comparison. It is crucial to ensure that the calves being samples haven’t been treated with antibiotics and this can lead to inaccurate results
Which faecal analysis tests can you do to diagnose the cause of calf scour?
Bacterial culture
Virology
Parasitology
ELISA
Why is it so important to diagnose the cause of calf scour?
It is important to diagnose the cause of calf scour in order to implement the correct prevention strategies
What are the consequences of calf scour?
Dehydration
Hypovolaemia
Pre-renal azotaemia
Electrolyte imbalances
Metabolic acidosis
Hyperkalaemia
What are the consequences of calf scour?
Dehydration
Hypovolaemia
Pre-renal azotaemia
Electrolyte imbalances
Metabolic acidosis
Hyperkalaemia
What causes metabolic acidosis in calf scour?
Intestinal bicarbonate loss
Bacterial production of lactate
Lactate production due to tissue hypoperfusion and anaerobic metabolism
Pre-renal azotaemia resulting in decreased GFR and excretion of hydrogen ions
What are the clinical signs of metabolic acidosis in calves?
Progressive depression
Decreased suckle reflex
Reduced to absent palpebral reflex
Weakness
Comatose
Which factor kills scouring calves?
Dehydration
Which factors should you focus on during a clinical examination of a calf with scour?
Demeanour
Hydration status
Respiratory rate
Nature of the scour
Temperature
Assess for metabolic acidosis
What is the main form of treatment for calf scour?
Fluid therapy
When is oral fluid therapy sutiable for the treatment of calf scour?
Oral fluid therapy is sutiable for the treatment of calf scour if the calf is less than 7% dehydrated with no clinical signs of metabolic acidosis
What are the aims of oral fluid therapy when treating calf scour?
Correct the fluid deficit
Provide alkalinising agents to improve the buffering capacity of the blood
Increase the strong ion difference by replacing lost sodium and potassium
Maintain blood glucose levels
(T/F) Milk should still be fed alongside oral fluid therapy when treating calf scour
TRUE. Oral fluid therapy is crucial for correcting dehydration and electrolyte imbalances, but milk provides essential nutrients like protein and energy that are necessary for recovery. However, do not mix milk and fluid therapy (feed 1.5 hours apart) as the electrolytes can intefere with casein digestion within the abomasum
When is intravenous fluid therapy required for the treatment of calf scour?
Intravenous fluid therapy should be used if the calf is between 7 - 9% dehydrated with clinical signs of mild metabolic acidosis
What is the maintenance fluid rate for calves?
50 - 100ml/kg/day
How may litres of fluid should be administered to scouring calves to accommodate ongoing losses?
2 - 3 litres/day
Which fluid type is best for IV treatment of scouring calves?
Hartmannn’s fluid
What is the fluid rate for intravenous fluid treatment of calf scour?
Administer IV fluids at a rate of 80ml/kg/hr for the first hour (i.e. fully open the giving set), and then reduce the rate to 30 - 50ml/kg/hr. Always follow up intravenous fluid therapy with oral fluid therapy
When is intravenous fluid therapy and 1.3% bicarbonate required for the treatment of calf scour?
Intravenous fluid therapy and 1.3% bicarbonate should be used in the treatment of calf scour if the calf is over 9% dehydrated with clinical signs of moderate to severe metabolic acidosi
How do you carry out a bicarbonate spike?
Add 13g of sodium bicarbonate to 1 litre of 0.9% NaCl or sterile water to form 1.3% bicarbonate
When is it appropriate to administer 1.3% bicarbonate to a scouring calf?
Only administer 1.3% bicarbonate if a calf is over 7 days old, you have corrected the fluid deficit with fluid therapy but they are still exhibiting clinical signs of metabolic acidosis
Why should you only administer 1.3% bicarbonate to calves over 7 days old?
Studies have shown that calves over 7 days old are much more likely to be in metabolic acidosis than calves less than 7 days old
How many litres of 1.3% bicarbonate should you administer to a scouring calf in sternal recumbency?
If the calf is less than or equal to 40kg and is in sternal recumbeny, administer 2 litres of 1.3% bicarbonate, however if they are above 40kg, administer 3 litres of 1.3% bicarbonate
How many litres of 1.3% bicarbonate should you administer to a scouring calf in lateral recumbency?
If the calf is less than or equal to 40kg and is in lateral recumbeny, administer 3 litres of 1.3% bicarbonate, however if they are above 40kg, administer 4 litres of 1.3% bicarbonate
What is the main contraindication 1.3% bicarbonate adminstration in calves?
You should never administer 1.3% bicarbonate to calves in severe respiratory distress
Why is 1.3% bicarbonate contraindicated in calves in severe respiratory distress?
Bicarbonate is a buffer which binds to H+ within the bloodstream to form carbonic acid which rapidly dissociates into CO2 and water, increasing serum CO2 levels in the blood. This can exacerbate hypercapnia and respiratory acidosis as ventilation will be compromised in patients in severe respiratory distress. This will also decrease the pH within the cerebrospinal fluid as the blood CO2 will diffuse into the cerebrospinal fluid, decreasing the pH. This can result alter CNS function and present clinically as muscle tremors and fasciculations (twitches)
Which adjunctive treatments can be used for calf scour?
Antimicrobials
Analgesia
Specific cryptosporidium parvum treatment
Specific coccidiosis treatment
Why is it contraindicated to administer oral antibiotics to animals that have diarrhoea?
Diarrhoea decreases gut transit time resulting in decreased absorption and bioavailability of the drug
When are antimicrobials indicated in the treatment of calf scour?
If you suspect E. coli or salmonella mediated scour
Systemic clinical signs indicating septicaemia or secondary small intestinal bacterial overgrowth (SIBO)
Blood in the scour
Which systemic clinical signs can indicate antimicrobials are required in the treatment of calf scour?
Pyrexia
Lethargy
Decreased appetite
Remember calves with scour are generally BAR
Which first line antibiotic should you use for calf scour?
Trimethoprim and potentiated sulphonamides (TMPS)
Which analgesia drugs can you use in the treatment of calf scour?
NSAIDs. However only when the fluid deficit is corrected as you risk nephrotoxicity
Which drug can be used to treat cryptosporidium parvum?
Halofuginone
Which drug can be used to treat and prevent coccidiosis?
Toltrazuril
What nursing care is required when treating calf scour (this will have to be done by the farmer)?
Isolation from other calves
Keep warm (i.e. use calf jackets)
Access to fresh, clean water
Feed milk alongside fluid therapy
Monitor response to treatment
