Clinical Pathology in large animals

Question 1

History
A 1-year-old Thoroughbred filly presents with projective watery diarrhoea of 2 weeks’ duration. The BCS is 1/5, with well visible ribs, tucked-up abdomen, undeveloped musculature of the hind limbs and forelimbs. The filly has dull demeanour. The heart rate is 60 beats per minute, respiratory rate is 12 breaths per minute and rectal temperature is 38.8C. Mucous membranes are tacky, dry with a CRT of 3 seconds. Gastrointestinal borborygmic are loud, watery on all quadrants. Digital pulses are palpable but not increased.

Interpret these results

Answer 1

• Increased PCV suggests haemoconcentration (dehydration, hypovolaemia)
  
  • Neutrophilia - due to inflammation (not stress as no lymphopenia present that glucocorticoids would cause)
  • Elevated lactate suggests poor perfusion (consistent with hypovolaemia)
  • Low albumin (+ TP) but no evidence of hepatic pathology so more likely due to excessive loss
  • Na and Cl being lost in similar amounts suggests loss in diarrhoea - this has an impact on circulating volume and perfusion than water alone
    Total Ca reduced as Ca bound to albumin lost (iCa probably not affected)

Question 2

History
A 23-year-old Shetland pony mare is examined for severe deficits in proprioception (grade 4/5) and inappetence. The menace response is delayed (PLR is normal).

Interpret these results

Answer 2

• Moderate monocytosis - stress or inflammation
  
  • Lactate suggested compromised perfusion
  • Elevated creatinine may have pre-renal origin consistent with hypovolaemia and poor perfusion
  • Hyperglycaemia suggests stress response (hepatic dysfunction not severe enough to have compromised glucose manufacture)
  • Liver enzymes indicate hepatic pathology
  • Functional tests indicate disrupted hepatobiliary function
    Ammonia provides evidence of porto-systemic shunting - this also explain neurological clinical signs (hepatic encephalopathy)

Question 3

HISTORY
A cow was presented to the University College Dublin (UCD) hospital with poor appetite, dullness and right hand side pinging of the abdomen on auscultation
EXAMINATON
Heart rate of 124 beats/minute, respiratory rate 24 breathes/minute and temperature 37.9⁰C. The cow had a mild skin tent, with pale pink moist mucus membranes and capillary refill time of 2 seconds. Rumen contractions were 1 per 90 seconds and were quiet, with a rumen fill of 2 out of 5. There was a ping on the right hand side on auscultation and percussion, which radiated from the 8th rib cranially to the 4th transverse lumbar caudally.

Interpret these results

Answer 3

Haematology:
* High neutrophil to lymphocyte ratio = Neutrophilia and lymphopaenia
* Band cells (immature neutrophils) suggests immune response is failing - could be the result of septicaemia
* Elevated mean cell haemoglobin is a machine error
Biochem:
* Increased lactate suggests hypovolaemic shock - lactate builds up as a result of anaerobic metabolism due to lack of clearance
* Elevated urea suggests pre-renal azotaemia - most likely due to hypovolaemia
* Decreased TP couod be due to protein losing enteropathy or liver damage (due to fatty liver)
* Mild increases in GGT and GLDH suggests hepatic cell damage (could be due to fatty liver or enlarged abomasum pressing on liver)
* Decreased K+ level:
○ Likely due to alkalosis - conc of K+ in extracellular fluid decreases due to exchange with H+
○ In alkalosis there is a shift to increase extracellular fluid H+ conc, so it can bind to excess HCO3- ions
○ K+ ions lost in urine as the exchange also happens in the kidney
○ Hypokalaemia could also be linked to decreased dieterary intake, which could also be responsible for the hyponatraemia
* Hypochloraemia
○ Could indicate retention of CL- in an organ such as caecum or abomasum
○ Sequestration of Cl- leads to relative excess of HCO3- which worsens the metabolic alkalosis
* Hypocalcaemia could be related to low TP levels (Ca bound to albumin in blood) or septicaemia
Acid-base:
* Indication of metabolic alkalosis due to elevatyed pH and elevated HCO3-
* Elevated pCO2 indicated respiratory acidosis (compensatory mechanism to alkalosis)
Base excess being positive confirm metabolic alkalosis

Question 4

HISTORY
A 9 day old Holstein dairy heifer, who has had diarrhoea for 3 days.
EXAMINATION FINDINGS
The heifer was recumbent, with sunken eyes and a CRT of 3 seconds. Temperature 36.9°C.

Interpret these results

Answer 4

Haematology:
* Inflammatory leukogram (neutrophilia and monocytosis)
* Signs of dehydration due to elevated PCV
Biochem:
* Marked hypoproteinaemia despite dehydration - could be due to liver disease, starvation or intestinal loss of protein
○ As there is likely failure of passive transfer - likely a combination of GI loss and failed passive transfer
* Hypoglycaemia - most likely due to decrease feed intake and sepsis
* Sepsis likely due to increased neutrophils
* BUN and serum creatinine levels are elevated - suggests azotaemia
* Increased phosphate could be normal for neonate - more likely due to decreased glomerular filtraiton rate
* Hypocalcaemia - could be related to hypoalbuminea
* Increased serum CK and AST indicated prolonged recumbency or hypoperfusion
* Increased GGT may reflect some colostrum absorption as colostrum contaiuns high GGT levels
* Increased NA and Cl ions indicated hypertonic dehydration - suggesting it is not secretory diarrhoea
* Despite K being lost in diarrhoea, likely there is a redistributional hyperkalaemia due to exchange of intracellular K for extracellular H+ in response to metabolic acidosis
* Respiratory acidosis suggests inadequate pulmonary perfusion/ventilation
Blood gas:
* Combined metabolic acidosis (decreased HCO3-) and respiratory acidosis (increased pCO2)
Metabolic acidosis from GI losses of HCO3- and build up of lactate in GIT and tissues from poor perfusion