• Bile acid synthesis in mammals and birds occurs in the liver and is the primary pathway in the metabolism of cholesterol, which is the precursor molecule for bile acid synthesis. • Bile acids are conjugated in the liver, to glycine or taurine, to inhibit intestinal bile acid resorption and promote lipid metabolism. Bacteria in the intestine further modify bile acids. • Bile acids are secreted via the bile duct into the small intestine and emulsify ingested fats to be solubilized for digestion and absorption. • In birds (with or without a gallbladder), secretion of bile acids is continuous. • As an indicator of the severity of a liver disease, avian values for enzymatic (spectrophotometer) methods are as follows (radioimmunoassay shows lower values):
Bile Acids
Physiology
Typical Normal Range
Although reference ranges for bile acid concentrations have not been established for all avian species, bile acid concentrations are considered to be elevated in pigeons and psittacine species if they are greater than 70 mmol/L in fasted (12-hour) samples. Postprandial bile acid concentrations vary between bird species and are challenging to interpret.
Liver Disease Severity
Bile Acid Values, µm/l
Minimal
50-150 µM/L
Mild
150-250 µM/L
Moderate
250-500 µM/L
Severe
500-700 µM/L
RIA
Colorimetric
Birds
psittacines
African grey parrot
18-71
12-96
Amazon parrots
19-144
33-154
Budgerigar parakeet
20-65
32-117
Caique
12-112
Cockatiel
25-85
15-139
Cockatoos
34-112
8-11
Conure
32-105
8-15
Eclectus parrot
30-110
8.8-9.8
Grey-cheek parakeet
15-96
Lory
20-97
Lovebird
25-95
12-90
Macaw
7-100
Pionus parrot
15-92
Quaker parrot
21-90
Senegal parrot
0-85
20-94
passeriformes and columbiformes
Canary
23-90
Pigeon
22-60
piciformes
Toucan
20-40
Emu
6-45
Ostrich
4-40
raptors
Peregrine falcon
20-118
Mammals
Guinea pig
57 µg/mL
Rat
56.0 ± 6.6 µmol/L (male) 27.7-41.1 µmol/L (female)
Ferret
0.0-8.0 µmol/L
1-28 µmol/L (mean, 9.1 µmol/L) for males
2-14 µmol/L (mean, 4.4 µmol/L) for females
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